Development of a Passenger Assistance System to Increase the Attractiveness of Local Public Transport

Abstract

In this paper, we present a concept for an assistance system for public transport passengers currently being developed for Kassel, Germany, and its surrounding area. The assistance system aims at increasing the attractiveness of local public transport by reducing barriers to use, thus promoting sustainable travel behavior. Three main barriers were identified: crowded vehicles, missed connections, and inconveniences in the transportation of shopping bags and luggage. To tackle these issues, three assistance system services were conceptualized: the occupancy rate informing passengers about the occupancy level of vehicles, the transfer connection monitor and secure system giving passengers the option to communicate transfer connection requests, and the delivery service allowing the use of public transport while shopping without the need to transport purchased goods. The three services are presented in detail along with the user interfaces they will be integrated into. Moreover, for the further implementation of the assistance system, a user requirement analysis is outlined. We finally give an overview and outlook regarding the implementation and evaluation of the concept in laboratory studies and a one-year field study.

Full text



Citation: Faulhaber, A.K.;
Hegenberg, J.; Kahnt, S.E.;
Lambrecht, F.; Leonhäuser, D.; Saake,
S.; Wehr, F.; Schmidt, L.; Sommer, C.
Development of a Passenger
Assistance System to Increase the
Attractiveness of Local Public
Transport. Sustainability 2022,14,
4151. https://doi.org/10.3390/
su14074151
Academic Editor: Thomas Schlegel
Received: 28 February 2022
Accepted: 29 March 2022
Published: 31 March 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
sustainability
Concept Paper
Development of a Passenger Assistance System to Increase the
Attractiveness of Local Public Transport
Anja K. Faulhaber 1, * , Jens Hegenberg 1, Sophie Elise Kahnt 2, Franz Lambrecht 2, Daniel Leonhäuser 2,
Stefan Saake 2, Franka Wehr 1, Ludger Schmidt 1and Carsten Sommer 2
1Human-Machine Systems Engineering Group, University of Kassel, 34125 Kassel, Germany;
j.hegenberg@uni-kassel.de (J.H.); f.wehr@uni-kassel.de (F.W.); l.schmidt@uni-kassel.de (L.S.)
2Transportation Planning and Traffic Systems, University of Kassel, 34125 Kassel, Germany;
sophie.kahnt@uni-kassel.de (S.E.K.); franz.lambrecht@uni-kassel.de (F.L.); leonhaeuser@uni-kassel.de (D.L.);
stefan.saake@uni-kassel.de (S.S.); c.sommer@uni-kassel.de (C.S.)
*Correspondence: a.faulhaber@uni-kassel.de
Abstract:
In this paper, we present a concept for an assistance system for public transport passengers
currently being developed for Kassel, Germany, and its surrounding area. The assistance system
aims at increasing the attractiveness of local public transport by reducing barriers to use, thus
promoting sustainable travel behavior. Three main barriers were identified: crowded vehicles, missed
connections, and inconveniences in the transportation of shopping bags and luggage. To tackle
these issues, three assistance system services were conceptualized: the occupancy rate informing
passengers about the occupancy level of vehicles, the transfer connection monitor and secure system
giving passengers the option to communicate transfer connection requests, and the delivery service
allowing the use of public transport while shopping without the need to transport purchased goods.
The three services are presented in detail along with the user interfaces they will be integrated into.
Moreover, for the further implementation of the assistance system, a user requirement analysis is
outlined. We finally give an overview and outlook regarding the implementation and evaluation of
the concept in laboratory studies and a one-year field study.
Keywords:
public transport; sustainable mobility; assistance system; occupancy forecast; passenger
information
1. Introduction
The German government’s climate protection goals for 2030 call for a reduction in
greenhouse gas emissions from road transport [
1
]. However, modern cities are still highly
dependent on motorized private transport, leading to higher emissions, urban automobile
congestion, and reduced quality of life [
2
]. Even though German metropolises usually
have a good range of local public transport, an average of 59% of passenger kilometers
are covered by motorized private transport [3]. To meet the defined goals in the transport
sector regarding climate protection, air pollutants, energy consumption, and land use, it
is necessary to reduce the use of private motorized transport significantly—especially in
urban areas. Studies indicate that emission factors of public transport are much lower
compared to car travel [
4
]. Taking advantage of these potential emission reductions requires
people to change their travel behavior towards more sustainable mobility solutions such as
public transport.
The literature suggests that travel behavior and travel mode choices are strongly
influenced by routines and habits [
5
–
7
]. Many studies have investigated how such habits
can be broken and how people can be persuaded to develop more sustainable travel
behavior. These studies include several kinds of incentives such as free tickets [
8
], gam-
ification applications [
9
–
12
], and motivational features such as self-monitoring feedback
Sustainability 2022,14, 4151. https://doi.org/10.3390/su14074151 https://www.mdpi.com/journal/sustainability

Sustainability 2022,14, 4151 2 of 17
and rewards [
13
,
14
]. Furthermore, several measures were suggested to discourage pri-
vate motorized transport while encouraging public transport [
15
]. Other studies include
persuasive technologies in the form of mobility or transit apps for multimodal travel and
Mobility-as-a-Service schemes [
16
–
18
]. These are just a few examples of an extensive and
rapidly growing body of literature (for relevant literature reviews see, e.g., [2,19,20]).
In general, an essential building block in the development of sustainable travel behav-
ior is reliable and attractive local public transport. This also entails that barriers preventing
people from using public transport need to be reduced. Such barriers include drawbacks
due to costs, comfort, and convenience, as well as restrictions regarding flexibility and
punctuality [
21
]. In addition, unreliable or limited information available to passengers
may lead to barriers. For example, Lopez-Carreiro et al. [
17
] report that passengers ex-
pect real-time information regarding passenger crowding, vehicle conditions, and route
planning, among others. However, the occupancy rates of local public transport vehicles
are commonly not communicated to passengers. Moreover, insecurities about transfer
connections, the inflexibility of public transport for shopping trips, and inconveniences of
transporting luggage affect which transport mode people choose [
22
–
25
]. These are barriers
that can be overcome. Digitalization and the spread of smartphones among passengers
offer a wide range of opportunities to increase the convenience of using public transport by
providing more real-time information and additional options. Digital technologies have
the potential to significantly impact travel behavior [26,27].
In this context, a concept for a public transport assistance system is presented here,
which tackles three main aspects of the aforementioned barriers—occupancy, transfer
connections, and luggage transportation. More precisely, the assistance system is being
developed within the scope of the project U
3
(full project title in German: U-hoch-3—
Unbeschwert urban unterwegs) with a project consortium composed of partners from industry,
local public transport companies, and academia. It has the objective to improve the travel
experience for passengers of the Nordhessischer Verkehrsverbund (NVV) in Kassel and its
surrounding area in Germany. Kassel is a city and regional center in northern Hesse with
around 200,000 inhabitants. The local public transport network spans across urban and
rural areas with buses and trams.
The assistance system comprises three services. The first one is an occupancy rate
service for predicting the occupancy levels of vehicles in general and of multipurpose
areas for wheelchairs, bicycles, etc., in particular. As mentioned previously, passengers
would prefer to receive information regarding the occupancy of vehicles, but this is com-
monly not communicated in local public transport. Only recently, interest in this topic
has grown due to the COVID-19 pandemic, which had a considerable impact on public
transport passengers. The intentions to use public transport were affected and people
preferred to choose solo modes of travel [
28
,
29
]. Therefore, it seems necessary to think
of new public transport planning methods in the context of the pandemic, e.g., to meet
the distancing requirements [
30
]. Providing passengers with information on occupancy
levels would be a possible solution in this regard. Additionally, the novelty of this service
stems especially from the occupancy prediction for the multipurpose areas via new sensors
allowing for object recognition. This may improve the accessibility for people traveling
with bicycles, baby carriages, etc., and particularly for disabled people with the potential
of improving their life satisfaction [
31
]. The second service of the assistance system is a
transfer connection monitor and secure (TCMS) system for real-time information regarding
connections. The service additionally includes the option for passengers to communicate a
transfer connection request, which is also a novel service in local public transport giving
the passengers a more active role in the connection planning process. The third service is a
delivery service for convenient use of public transport while shopping without the need to
transport shopping bags. This service aims to persuade people to use public transport for
shopping trips instead of their cars.
After a user requirement analysis, these services will first be implemented prototypi-
cally and evaluated in laboratory studies. Afterwards, the services will be implemented

Sustainability 2022,14, 4151 3 of 17
for selected NVV lines and evaluated in a one-year field study to derive recommendations.
In conclusion, the objective of the concept is to make public transport more attractive by
reducing the aforementioned barriers and thus supporting people in the development
towards more sustainable travel behavior.
In the following, the assistance system concept and the three services are described in
more detail in Section 2. To implement the assistance system, additional information must
be integrated into existing user interfaces. Thus, Section 3gives an overview of user inter-
faces included in the concept. Furthermore, for the assistance system to be successful, it is
imperative to know user needs. Therefore, a comprehensive user requirement analysis was
conducted and is outlined in Section 4. Section 5delineates the prototypical implementation
and evaluation in laboratory studies of components of the assistance system. Section 6
provides an outlook on the holistic evaluation of the assistance system in a one-year field
study before conclusions are derived in Section 7.
2. Assistance System for Public Transport Passengers
The developed assistance system intends to make local public transport more attractive,
thereby contributing to the achievement of the Sustainable Development Goals (SDGs)
of the United Nations Agenda 2030 [
32
]. The implementation of the assistance system is
particularly intended to positively contribute to the achievement of the SDGs described in
Table 1.
Table 1.
The assistance system in connection with the Sustainable Development Goals of the United
Nations Agenda 2030 [32].
Sustainable Development Goals Description
Sustainability 2022, 14, x FOR PEER REVIEW 3 of 18
for selected NVV lines and evaluated in a one-year field study to derive recommenda-
tions. In conclusion, the objective of the concept is to make public transport more attrac-
tive by reducing the aforementioned barriers and thus supporting people in the develop-
ment towards more sustainable travel behavior.
In the following, the assistance system concept and the three services are described
in more detail in Section 2. To implement the assistance system, additional information
must be integrated into existing user interfaces. Thus, Section 3 gives an overview of user
interfaces included in the concept. Furthermore, for the assistance system to be successful,
it is imperative to know user needs. Therefore, a comprehensive user requirement analysis
was conducted and is outlined in Section 4. Section 5 delineates the prototypical imple-
mentation and evaluation in laboratory studies of components of the assistance system.
Section 6 provides an outlook on the holistic evaluation of the assistance system in a one-
year field study before conclusions are derived in Section 7.
2. Assistance System for Public Transport Passengers
The developed assistance system intends to make local public transport more attrac-
tive, thereby contributing to the achievement of the Sustainable Development Goals
(SDGs) of the United Nations Agenda 2030 [32]. The implementation of the assistance sys-
tem is particularly intended to positively contribute to the achievement of the SDGs de-
scribed in Table 1.
Table 1. The assistance system in connection with the Sustainable Development Goals of the United
Nations Agenda 2030 [32].
Sustainable Development Goals Description
The aim of the assistance system is to make local public transport more reliable and
comfortable for passengers and, thus, to increase their sense of well-being when us-
ing buses and trains. The information on occupancy rate can also lead to the avoid-
ance of crowded vehicles, especially during pandemics such as COVID-19, thus re-
ducing the risk of infection [33].
The assistance system expands access to information and communication technolo-
gies in local public transport. The contribution to this SDG can also be understood
as a contribution to the smart city development concept. Digital applications in lo-
cal public transport, such as the three services developed, increase the level of infor-
mation, accessibility, reliability, and simplicity of using buses and trams via mobile
apps and websites and thus contribute to a turn towards smart mobility [34].
The assistance system helps ensure that people have access to a safe and sustainable
public transportation system in Kassel and its surrounding area. In contrast to pri-
vate motorized transport, the use of local public transport contributes to lower pol-
lutant emissions, less land use, and a higher quality of life in the city [35].
The assistance system aims to increase the level of attractiveness by using public
transport in Kassel and its surrounding area. This creates an incentive to use buses
and trams instead of private cars. One contribution of the transport sector to cli-
mate protection is the reduction of greenhouse gas emissions by reducing private
motorized transport [36].
The aim of the assistance system is to make local public transport more reliable and
comfortable for passengers and, thus, to increase their sense of well-being when using buses
and trains. The information on occupancy rate can also lead to the avoidance of crowded
vehicles, especially during pandemics such as COVID-19, thus reducing the risk of
infection [33].
Sustainability 2022, 14, x FOR PEER REVIEW 3 of 18
for selected NVV lines and evaluated in a one-year field study to derive recommenda-
tions. In conclusion, the objective of the concept is to make public transport more attrac-
tive by reducing the aforementioned barriers and thus supporting people in the develop-
ment towards more sustainable travel behavior.
In the following, the assistance system concept and the three services are described
in more detail in Section 2. To implement the assistance system, additional information
must be integrated into existing user interfaces. Thus, Section 3 gives an overview of user
interfaces included in the concept. Furthermore, for the assistance system to be successful,
it is imperative to know user needs. Therefore, a comprehensive user requirement analysis
was conducted and is outlined in Section 4. Section 5 delineates the prototypical imple-
mentation and evaluation in laboratory studies of components of the assistance system.
Section 6 provides an outlook on the holistic evaluation of the assistance system in a one-
year field study before conclusions are derived in Section 7.
2. Assistance System for Public Transport Passengers
The developed assistance system intends to make local public transport more attrac-
tive, thereby contributing to the achievement of the Sustainable Development Goals
(SDGs) of the United Nations Agenda 2030 [32]. The implementation of the assistance sys-
tem is particularly intended to positively contribute to the achievement of the SDGs de-
scribed in Table 1.
Table 1. The assistance system in connection with the Sustainable Development Goals of the United
Nations Agenda 2030 [32].
Sustainable Development Goals Description
The aim of the assistance system is to make local public transport more reliable and
comfortable for passengers and, thus, to increase their sense of well-being when us-
ing buses and trains. The information on occupancy rate can also lead to the avoid-
ance of crowded vehicles, especially during pandemics such as COVID-19, thus re-
ducing the risk of infection [33].
The assistance system expands access to information and communication technolo-
gies in local public transport. The contribution to this SDG can also be understood
as a contribution to the smart city development concept. Digital applications in lo-
cal public transport, such as the three services developed, increase the level of infor-
mation, accessibility, reliability, and simplicity of using buses and trams via mobile
apps and websites and thus contribute to a turn towards smart mobility [34].
The assistance system helps ensure that people have access to a safe and sustainable
public transportation system in Kassel and its surrounding area. In contrast to pri-
vate motorized transport, the use of local public transport contributes to lower pol-
lutant emissions, less land use, and a higher quality of life in the city [35].
The assistance system aims to increase the level of attractiveness by using public
transport in Kassel and its surrounding area. This creates an incentive to use buses
and trams instead of private cars. One contribution of the transport sector to cli-
mate protection is the reduction of greenhouse gas emissions by reducing private
motorized transport [36].
The assistance system expands access to information and communication technologies in
local public transport. The contribution to this SDG can also be understood as a contribution
to the smart city development concept. Digital applications in local public transport, such as
the three services developed, increase the level of information, accessibility, reliability, and
simplicity of using buses and trams via mobile apps and websites and thus contribute to a
turn towards smart mobility [34].
Sustainability 2022, 14, x FOR PEER REVIEW 3 of 18
for selected NVV lines and evaluated in a one-year field study to derive recommenda-
tions. In conclusion, the objective of the concept is to make public transport more attrac-
tive by reducing the aforementioned barriers and thus supporting people in the develop-
ment towards more sustainable travel behavior.
In the following, the assistance system concept and the three services are described
in more detail in Section 2. To implement the assistance system, additional information
must be integrated into existing user interfaces. Thus, Section 3 gives an overview of user
interfaces included in the concept. Furthermore, for the assistance system to be successful,
it is imperative to know user needs. Therefore, a comprehensive user requirement analysis
was conducted and is outlined in Section 4. Section 5 delineates the prototypical imple-
mentation and evaluation in laboratory studies of components of the assistance system.
Section 6 provides an outlook on the holistic evaluation of the assistance system in a one-
year field study before conclusions are derived in Section 7.
2. Assistance System for Public Transport Passengers
The developed assistance system intends to make local public transport more attrac-
tive, thereby contributing to the achievement of the Sustainable Development Goals
(SDGs) of the United Nations Agenda 2030 [32]. The implementation of the assistance sys-
tem is particularly intended to positively contribute to the achievement of the SDGs de-
scribed in Table 1.
Table 1. The assistance system in connection with the Sustainable Development Goals of the United
Nations Agenda 2030 [32].
Sustainable Development Goals Description
The aim of the assistance system is to make local public transport more reliable and
comfortable for passengers and, thus, to increase their sense of well-being when us-
ing buses and trains. The information on occupancy rate can also lead to the avoid-
ance of crowded vehicles, especially during pandemics such as COVID-19, thus re-
ducing the risk of infection [33].
The assistance system expands access to information and communication technolo-
gies in local public transport. The contribution to this SDG can also be understood
as a contribution to the smart city development concept. Digital applications in lo-
cal public transport, such as the three services developed, increase the level of infor-
mation, accessibility, reliability, and simplicity of using buses and trams via mobile
apps and websites and thus contribute to a turn towards smart mobility [34].
The assistance system helps ensure that people have access to a safe and sustainable
public transportation system in Kassel and its surrounding area. In contrast to pri-
vate motorized transport, the use of local public transport contributes to lower pol-
lutant emissions, less land use, and a higher quality of life in the city [35].
The assistance system aims to increase the level of attractiveness by using public
transport in Kassel and its surrounding area. This creates an incentive to use buses
and trams instead of private cars. One contribution of the transport sector to cli-
mate protection is the reduction of greenhouse gas emissions by reducing private
motorized transport [36].
The assistance system helps ensure that people have access to a safe and sustainable public
transportation system in Kassel and its surrounding area. In contrast to private motorized
transport, the use of local public transport contributes to lower pollutant emissions, less land
use, and a higher quality of life in the city [35].
Sustainability 2022, 14, x FOR PEER REVIEW 3 of 18
for selected NVV lines and evaluated in a one-year field study to derive recommenda-
tions. In conclusion, the objective of the concept is to make public transport more attrac-
tive by reducing the aforementioned barriers and thus supporting people in the develop-
ment towards more sustainable travel behavior.
In the following, the assistance system concept and the three services are described
in more detail in Section 2. To implement the assistance system, additional information
must be integrated into existing user interfaces. Thus, Section 3 gives an overview of user
interfaces included in the concept. Furthermore, for the assistance system to be successful,
it is imperative to know user needs. Therefore, a comprehensive user requirement analysis
was conducted and is outlined in Section 4. Section 5 delineates the prototypical imple-
mentation and evaluation in laboratory studies of components of the assistance system.
Section 6 provides an outlook on the holistic evaluation of the assistance system in a one-
year field study before conclusions are derived in Section 7.
2. Assistance System for Public Transport Passengers
The developed assistance system intends to make local public transport more attrac-
tive, thereby contributing to the achievement of the Sustainable Development Goals
(SDGs) of the United Nations Agenda 2030 [32]. The implementation of the assistance sys-
tem is particularly intended to positively contribute to the achievement of the SDGs de-
scribed in Table 1.
Table 1. The assistance system in connection with the Sustainable Development Goals of the United
Nations Agenda 2030 [32].
Sustainable Development Goals Description
The aim of the assistance system is to make local public transport more reliable and
comfortable for passengers and, thus, to increase their sense of well-being when us-
ing buses and trains. The information on occupancy rate can also lead to the avoid-
ance of crowded vehicles, especially during pandemics such as COVID-19, thus re-
ducing the risk of infection [33].
The assistance system expands access to information and communication technolo-
gies in local public transport. The contribution to this SDG can also be understood
as a contribution to the smart city development concept. Digital applications in lo-
cal public transport, such as the three services developed, increase the level of infor-
mation, accessibility, reliability, and simplicity of using buses and trams via mobile
apps and websites and thus contribute to a turn towards smart mobility [34].
The assistance system helps ensure that people have access to a safe and sustainable
public transportation system in Kassel and its surrounding area. In contrast to pri-
vate motorized transport, the use of local public transport contributes to lower pol-
lutant emissions, less land use, and a higher quality of life in the city [35].
The assistance system aims to increase the level of attractiveness by using public
transport in Kassel and its surrounding area. This creates an incentive to use buses
and trams instead of private cars. One contribution of the transport sector to cli-
mate protection is the reduction of greenhouse gas emissions by reducing private
motorized transport [36].
The assistance system aims to increase the level of attractiveness by using public transport in
Kassel and its surrounding area. This creates an incentive to use buses and trams instead of
private cars. One contribution of the transport sector to climate protection is the reduction of
greenhouse gas emissions by reducing private motorized transport [36].

Sustainability 2022,14, 4151 4 of 17
As mentioned previously, the assistance system is composed of three services
(Figure 1).
In a preliminary study, passengers, experts from the public transport sector as well as from
courier, express, and parcel (CEP) service providers, and retail sectors were systematically
surveyed. Passengers found it inconvenient to transport luggage on buses and trams
and were particularly interested in information about their desired connections and oc-
cupancy levels of vehicles. The public transport experts also saw the issue of connection
security as a significant quality criterion in public transport. According to them, the lack
or disuse of real-time data has been the main obstacle to the effective use of connection
information. A representation of the occupancy rate has failed so far primarily because of
the lack of area-wide use of automatic passenger counting data due mainly to economic
reasons [
37
]. Based on these insights combined with the literature review, the three services
were conceptualized as described in more detail in the following.
Sustainability 2022, 14, x FOR PEER REVIEW 4 of 18
As mentioned previously, the assistance system is composed of three services (Figure
1). In a preliminary study, passengers, experts from the public transport sector as well as
from courier, express, and parcel (CEP) service providers, and retail sectors were system-
atically surveyed. Passengers found it inconvenient to transport luggage on buses and
trams and were particularly interested in information about their desired connections and
occupancy levels of vehicles. The public transport experts also saw the issue of connection
security as a significant quality criterion in public transport. According to them, the lack
or disuse of real-time data has been the main obstacle to the effective use of connection
information. A representation of the occupancy rate has failed so far primarily because of
the lack of area-wide use of automatic passenger counting data due mainly to economic
reasons [37]. Based on these insights combined with the literature review, the three ser-
vices were conceptualized as described in more detail in the following.
Figure 1. The three services of the assistance system for public transport passengers.
2.1. Occupancy Rate
The first service of the assistance system tackles the issues concerning the lack of in-
formation on occupancy rates in local public transport. In the U3 project, different fore-
casting models are being designed, technically implemented, and tested in the one-year
field study. The aim is, on the one hand, to forecast the passenger load of vehicles in local
public transport and, on the other hand, to predict the occupancy of the multipurpose
areas of these vehicles. Multipurpose areas are special areas in the vehicles where wheel-
chairs, baby carriages, bikes, and other larger objects can be placed.
From the passengers’ point of view, a reliable forecast serves to increase comfort and
reduce barriers to use [38]. Passengers can decide for or against certain connections based
on knowledge about the occupancy rate. Mobility-impaired passengers can assess
whether capacities are available in the desired vehicle. From the transport companies’
point of view, forecasting models offer the possibility of supporting deployment planning
and of being able to deploy the available vehicles in a more targeted manner [39]. In ad-
dition, passenger flows can be managed so that peak loads can be avoided and a more
even utilization can be achieved [40].
There are several possible data types and data sources available for designing fore-
casting models in public transport. In other projects, for example, automatic vehicle loca-
tion (AVL) data and automated fare collection (AFC) data were used [41]. Another ap-
proach is to use data collected by query logs [42]. These sources often have gaps in their
data. AFC data, for example, exclude a lot of passengers who do not buy their tickets via
the respective app from which the data are available or via an app at all [43]. Query log
data are, in many cases, not reliable since people tend to search for more than one connec-
tion, and it is not known which vehicle they actually chose.
Figure 1. The three services of the assistance system for public transport passengers.
2.1. Occupancy Rate
The first service of the assistance system tackles the issues concerning the lack of
information on occupancy rates in local public transport. In the U
3
project, different
forecasting models are being designed, technically implemented, and tested in the one-year
field study. The aim is, on the one hand, to forecast the passenger load of vehicles in local
public transport and, on the other hand, to predict the occupancy of the multipurpose areas
of these vehicles. Multipurpose areas are special areas in the vehicles where wheelchairs,
baby carriages, bikes, and other larger objects can be placed.
From the passengers’ point of view, a reliable forecast serves to increase comfort and
reduce barriers to use [
38
]. Passengers can decide for or against certain connections based
on knowledge about the occupancy rate. Mobility-impaired passengers can assess whether
capacities are available in the desired vehicle. From the transport companies’ point of view,
forecasting models offer the possibility of supporting deployment planning and of being
able to deploy the available vehicles in a more targeted manner [
39
]. In addition, passenger
flows can be managed so that peak loads can be avoided and a more even utilization can
be achieved [40].
There are several possible data types and data sources available for designing forecast-
ing models in public transport. In other projects, for example, automatic vehicle location
(AVL) data and automated fare collection (AFC) data were used [
41
]. Another approach
is to use data collected by query logs [
42
]. These sources often have gaps in their data.
AFC data, for example, exclude a lot of passengers who do not buy their tickets via the
respective app from which the data are available or via an app at all [
43
]. Query log data
are, in many cases, not reliable since people tend to search for more than one connection,
and it is not known which vehicle they actually chose.
The forecasting models in the U
3
project are mainly based on the analysis and process-
ing of automatic passenger counting (APC) data. Since almost all vehicles of the NVV are
supplied with counting systems, this is a reliable database. Although several sources of

Sustainability 2022,14, 4151 5 of 17
error exist (e.g., misuse by operators, defective devices, or wrong data preparation), the
advantages outweigh the disadvantages for this use case [
44
]. The main advantage of APC
data is that every person entering the vehicle is counted, so there is no need for projections,
which eliminates an additional possible source of error. Several other data sources are used
to further enrich the APC data: timetable, weather, capacity, and calendar data. Depending
on the particular model, different or additional data are used. The forecasting models in
the U
3
project can be divided into two groups depending on the subject of the forecast:
forecasting the occupancy level of the vehicle or forecasting the occupancy level of the
multipurpose areas. Both concepts are briefly introduced in the following.
The goal of vehicle occupancy forecasting is to predict how many passengers will be
in the vehicle at a given time in the future. In this project, this always involves forecasting
passenger demand on an edge, i.e., a section of a scheduled trip between two stops. A
key aspect of this service is the point in time of the forecast calculation. Depending on
the lead time, different models are used. If the vehicle has not yet started the trip, the
so-called long-term forecast is calculated. If the vehicle has already departed, the so-called
short-term forecast is used. The models differ in the data used for the calculation. While
long-term forecasting can only rely on historical counting data, short-term forecasting
includes real-time data.
Since the short-term forecasting model builds on the long-term forecasting model, the
long-term forecasting will be explained first. The long-term forecast model enables the
system to calculate a forecast for any edge in the NVV network for any time in the future.
For this purpose, the edge, for which a forecast is to be calculated, is categorized based on
certain stratification features. These stratification features are edge (edge to be forecast),
line (ID of the line), hour (hour in which the edge will be served), school day (is there school
operation on this day?), day type (categorization of the day into one of five categories), and
temperature class (categorization of the temperature into one of four temperature classes).
These stratification characteristics are used to search for comparable data points in the
historical trip data set. After removing outliers, a mean value is assumed to be the forecast
value. This forecast value is assigned to an occupancy rate after a comparison with the
vehicle capacity. In U3, there are four occupancy levels:
1. Less than 50% of the seats are occupied.
2. Less than 100% and more than 50% of the seats are occupied.
3. All seats are occupied, but less than 85% of the total capacity is occupied.
4. At least 85% of the total capacity is occupied.
The short-term forecast extends the model of the long-term forecast with real-time data
and consequently ensures a higher forecast quality. In simple terms, the difference between
the current occupancy (measured in real time) and the previously predicted long-term
forecast is calculated at each edge of a line trip. The resulting error is projected onto the
remaining edges of this particular line trip. Thus, the short-term forecast updates after each
stop of a line trip. The short-term forecast model can therefore map unexpected deviations
in occupancy patterns.
The second goal in U
3
regarding forecasting models is to predict the occupancy of the
multipurpose areas. To this end, all vehicles of a pilot line will be equipped with new sensor
technology capable of distinguishing between different object types. The model should be
able to display the current real-time occupancy but also to calculate forecasts for future
occupancy rates for multipurpose areas. A particular challenge here is that the occupancy
of a multipurpose area is a less frequent and potentially more irregular event compared
to the general vehicle occupancy. Data analysis will show whether certain patterns can be
identified to calculate reliable forecasts. Forecasting multipurpose area occupancy is a clear
added value for mobility-impaired individuals and is, therefore, targeted in the U
3
project.
So far, the models for short-term and long-term forecasting have been designed and
tested based on real counting data and are being developed for real operation. In the next
step, the counting data of the new sensor technology, which is able to distinguish different
object types, are analyzed. Subsequently, a model is developed to forecast the occupancy of

Sustainability 2022,14, 4151 6 of 17
the multipurpose areas. The information regarding occupancy rates is finally integrated
into several user interfaces for the field study, as explained further below.
2.2. Transfer Connection Monitor and Secure System
The second service of the assistance system targets local public transport transfer
connections. Missed transfer connections constitute one of the main obstacles for passengers
using public transport [
45
,
46
]. Additional waiting time on the transfer stop depending on
the frequency of service results in a lack of comfort for the passengers. Public transport
companies try to reduce the problem of these broken links by securing some of the transfers
manually or automatically. These so-called planned transfers are chosen depending on the
transfer connection importance in the public transportation network. Planned transfers
are often located at stations where buses can wait for trains with a higher passenger load
to distribute the demand further on. Another common application for planned transfers
is the last connection of a day. If the connection cannot be secured for the passengers to
transfer, there would not be an appropriate way to continue their trip with public transport.
Therefore, the connection has to be secured, if possible.
Securing a planned transfer is often realized by radio communication between drivers
and their operations control center. This solution is not efficient because of the manual
workload in the control center and its limited personal resources. Transfers between lines
operated by different public transport companies are another problem. They have different
control centers, and if they are coordinated at all, the communication effort increases.
The key advantage of a manually secured transfer is the possibility to solve problems
individually. Furthermore, passengers in the feeder line can ask their driver to request a
secured transfer at a certain station via radio communication. Besides manually secured
transfers, an intermodal transport control system (ITCS) can monitor planned transfers
automatically. The ITCS takes into account the delay of all vehicles involved and instructs
drivers via an on-board computer to wait if necessary. Above a certain size of the public
transport network, this solution is necessary because of the much higher efficiency. The
main problem of this approach is the unknown passenger demand at the transfer. The
system may secure a connection where no passengers transfer at all. In addition, public
transportation networks are often complex, with various dependencies and competing
demands, so that a waiting command at one station results in a delay and a chain reaction
leading to more necessary waiting commands for following transfer connections. For these
reasons, it is not practicable to secure every transfer automatically [47].
Within the project U
3
, a new approach of a TCMS system is developed and tested in the
NVV. The main advantage of this new solution is the option for the passengers to request a
certain transfer connection via a mobile app or an in-vehicle terminal. The NVV’s ITCS, or
another ITCS if involved knowing the demand for transfers, can then secure the relevant
transfer connections. This system can operate almost automatically, and the control center
operators can concentrate on individual problems in the operation processes. The new
system is realized by an update of the existing mobile app (NVV app) and a similar interface
on in-vehicle terminals (see also Section 3), representing the front end. The ITCS as part of
the back end receives an update too, to receive the messages generated and processed by
preceding system components and generate monitored transfer connections. If vehicle A
arrives with a delay at a monitored transfer connection and a delayed departure for vehicle
B is possible without intolerable negative operational consequences, the driver of vehicle B
receives the order to wait from the responsible ITCS via the on-board computer (secured
transfer). The passengers receive updated information about their requested transfer
connection via in-vehicle displays or the mobile app (Figure 2). This is a major increase in
comfort because the status of the transfer is communicated clearly to the passengers so that
they do not need to fear missing their connection due to delays. If the connection cannot be
secured because of too much delay or other circumstances, the new system will suggest
alternative connections instead of leaving the passengers alone with the problem.

Sustainability 2022,14, 4151 7 of 17
Sustainability 2022, 14, x FOR PEER REVIEW 7 of 18
board computer (secured transfer). The passengers receive updated information about
their requested transfer connection via in-vehicle displays or the mobile app (Figure 2).
This is a major increase in comfort because the status of the transfer is communicated
clearly to the passengers so that they do not need to fear missing their connection due to
delays. If the connection cannot be secured because of too much delay or other circum-
stances, the new system will suggest alternative connections instead of leaving the pas-
sengers alone with the problem.
Figure 2. Schematic sketch of the transfer connection monitor and secure (TCMS) system. (ITCS =
intermodal transport control system.)
2.3. Delivery Service
The third assistance system service refers to inconveniences of transporting shopping
bags or luggage in local public transport. As this is a major barrier to the use of public
transport [48], cars are often used for shopping trips instead. Car drivers use their vehicles
not only to transport their purchases but also to store them temporarily. To enable public
transport users to have a comparably comfortable shopping experience in the city center,
a delivery service is planned in cooperation with retailers and public transport providers.
This service will deliver goods purchased in the city center to the customers’ homes at a
chosen time. Furthermore, parcel stations are to be installed in the city center, which can
be used by public transport users both for handover to the delivery service and for tem-
porary storage.
The two services occupancy rate and TCMS system described above aim directly at
making public transport more attractive. The associated reduction in motorized private
transport can increase the attractiveness of living in the city. To avoid counteracting this
effect with the new delivery service and to include the problem of delivery traffic, which
is increasing anyway due to online retailing, aspects of city logistics are to be considered
for both the first and the last mile. To this end, the approach of centralizing flows of goods
needs to be considered. In a hybrid approach, the parcel stations installed in the city center
will also function as micro depots. CEP service providers deliver to them once by means
of a motorized vehicle. Customers can then either pick up the goods themselves or have
them delivered over the last mile using small electric vehicles, e.g., cargo bikes. Goods
Figure 2.
Schematic sketch of the transfer connection monitor and secure (TCMS) system.
(ITCS = intermodal transport control system.)
2.3. Delivery Service
The third assistance system service refers to inconveniences of transporting shopping
bags or luggage in local public transport. As this is a major barrier to the use of public
transport [
48
], cars are often used for shopping trips instead. Car drivers use their vehicles
not only to transport their purchases but also to store them temporarily. To enable public
transport users to have a comparably comfortable shopping experience in the city center, a
delivery service is planned in cooperation with retailers and public transport providers.
This service will deliver goods purchased in the city center to the customers’ homes at
a chosen time. Furthermore, parcel stations are to be installed in the city center, which
can be used by public transport users both for handover to the delivery service and for
temporary storage.
The two services occupancy rate and TCMS system described above aim directly at
making public transport more attractive. The associated reduction in motorized private
transport can increase the attractiveness of living in the city. To avoid counteracting this
effect with the new delivery service and to include the problem of delivery traffic, which
is increasing anyway due to online retailing, aspects of city logistics are to be considered
for both the first and the last mile. To this end, the approach of centralizing flows of goods
needs to be considered. In a hybrid approach, the parcel stations installed in the city center
will also function as micro depots. CEP service providers deliver to them once by means of
a motorized vehicle. Customers can then either pick up the goods themselves or have them
delivered over the last mile using small electric vehicles, e.g., cargo bikes. Goods deposited
by retailers or customers can be taken by the CEP service providers accordingly. Suitable
small electric vehicles can also improve the accessibility of retailers in city centers, who are
often not accessible at all with motorized vehicles or only for a limited time frame. This
also reduces parking pressure in the city center.
If the parcel stations in the city center are opened up to other CEP service providers,
online retail customers may frequent them and nearby stores occasionally. This can help
to strengthen local retail. Outside the city center, parcel stations open to all or most CEP
service providers should be set up at larger public transport stations to support delivery

Sustainability 2022,14, 4151 8 of 17
to end customers on the last mile. This approach is already successfully tested, e.g., in
Hamburg [
49
]. In addition to collection by the customer, the use of small electric vehicles
for delivery is also planned. Large public transport stops offer the necessary space and
facilitate use, especially for public transport passengers.
With parcel stations in the city center and at public transport stops in outlying districts,
goods can be transported via public transport. This approach can also be used to transport
goods from logistics centers into the city. A concept for this was developed as part of the
U
3
project, but it cannot be implemented as part of the field study due to hurdles such as
labor laws.
An alternative to delivery by employees with small electric vehicles is robot-assisted
delivery [
50
,
51
]. This will also be considered as part of the delivery service in U
3
. Since a
trial in a public space would generate greater legal, technical, and organizational expenses,
the approach is to be tested in a shopping center. The shopping center, with its aisles lined
with retail stores, is an analogy to pedestrian zones in the city center. Legal aspects are
easier to solve in a semi-public space and the technology does not have to be designed to
be, e.g., weatherproof. In the shopping center, customers can drop off their purchases for
delivery at the checkout. Robots should collect these deliveries and make them available
for a CEP service provider at a central pickup location. The first studies regarding the
application of this robot-assisted delivery are currently being conducted in the laboratory
and will be expanded to the shopping center.
3. User Interfaces
The previous sections have described the three assistance system services. Implement-
ing these services for passengers of public transport means that further information needs
to be integrated into existing user interfaces. The complexity of the concept suggests a need
for further research concerning the user-friendly presentation of information and interface
design. Thus, in the project, prototypes of the interfaces are designed and evaluated before
they are tested in the field study. The user interfaces considered in the U
3
project can be
grouped into two categories—interfaces for passengers and interfaces for public transport
operators such as drivers and control center operators.
The interfaces for passengers considered are, on the one hand, personal mobile devices
such as smartphones constituting the preferred interface, particularly for younger public
transport users [
37
]. This includes the NVV app as well as the website, which can be
accessed via smartphones. Additionally, more novel and innovative mobile devices such as
smartwatches and smart glasses are considered. Mobile devices are intended to provide
information about occupancy rates and the status of connections as well as the option to
request a transfer connection. On the other hand, publicly accessible user interfaces are
also considered. These refer to dynamic passenger information displays (DPI displays),
in-vehicle displays, in-vehicle terminals, and public displays. The DPI displays are located
at bus stops and tram stations and provide information on the scheduled arrival times
of incoming vehicles as well as their occupancy rates in general and in relation to the
multipurpose areas. The in-vehicle display provides information about connections and
their status. The in-vehicle terminal additionally provides the option to communicate a
connection request. Public displays provide information about occupancy rates of vehicles
at nearby stations and offer the option of having goods purchased in retail stores delivered
to the passengers’ homes.
The interfaces for public transport operators refer to on-board computers and con-
trol center software. Via the on-board computer, drivers receive both information about
connections to be held and connections that have been held, as well as information about
the recorded occupancy of their vehicle. They can give their own feedback on the latter if
requested to do so by the control center. Since the control center coordinates the connec-
tions, the corresponding functions also need be displayed in the control center software. It
must also be possible to transmit the information about the occupancy rate to the control
center and visualize it there. To implement the assistance system concept and integrate the

Sustainability 2022,14, 4151 9 of 17
three services adequately into the described user interfaces, a user requirement analysis
was conducted as outlined in the following section.
4. User Requirement Analysis
The literature suggests that to develop systems or products, one first needs to under-
stand the users and their needs [
52
]. Thus, a user requirement analysis was conducted
combining different methods to gain a thorough understanding of user needs [
53
]. This
resulted in a user requirement analysis composed of several phases, as we explain in
the following.
In the initial phase of the project, the objective was to reach as many passengers as
possible to gather information regarding user requirements in the context of the assistance
system concept. Therefore, an online survey was designed and completed by 385 par-
ticipants. To reach elderly passengers and people with disabilities, an offline version of
the survey was conducted with 41 elderly or disabled participants. The user survey was
complemented with interviews with five public transport experts. The results indicated that
passengers thought the concept could make public transport more attractive. Particularly,
the connection request feature was important to passengers as well as experts (for more
detailed results, see [37]).
Following up on the results from the surveys, focus groups were conducted for each
of the three assistance system services. By using the focus group technique, a more open,
qualitative method was applied, aiming at an in-depth exploration of user needs for each
one of the services [
54
]. The focus groups were conducted online with small groups of two
to five participants. The procedure always started with a short introduction to the respective
topic. Afterward, participants brainstormed and wrote down their ideas regarding current
issues and ideas for improvement in the context of the respective assistance system service
on an online whiteboard. Then, a moderated discussion started where the participants
presented their ideas and engaged in conversations with each other. Finally, participants
prioritized both the issues and the ideas for improvement according to how important
they were to them personally. Eleven online focus groups were completed this way with
30 participants. Additionally, eight phone interviews were carried out with participants
who could not or did not want to participate in the online focus groups. This led to a
total sample of 38 participants (19 female and 19 male) with ages ranging between 19 and
75 years (M = 37.9 years, SD = 18.7 years). The data were analyzed by consolidating and
counting aspects mentioned by the participants.
The results of the focus groups showed that participants saw merit in information re-
garding the occupancy level. It was mentioned most frequently that occupancy information
could be used to better distribute passengers across vehicles. Moreover, it was important
to participants that information regarding occupancy rates is available on various user
interfaces such as the NVV app, the website, and the DPI displays. In the context of the
TCMS system, the aspect mentioned most frequently was that information regarding con-
nections needs to be accurate and reliable, and should be presented on in-vehicle displays.
For the delivery service, participants were mostly concerned about the associated costs for
the users. Moreover, the sustainability of the delivery service, using, e.g., cargo bikes or
electric vehicles, was an important aspect. Based on these results and including further
less frequently mentioned aspects, a list of user requirements was derived for each service
ordered by priority depending on how many times certain aspects were mentioned and
how the participants prioritized them.
To complement the list of user requirements with a further perspective, requirements
were additionally collected systematically within the project consortium. Everybody was
asked to brainstorm user requirements for given contexts of use and the relevant user
interfaces. All the responses were collected and consolidated to create a composite list of
user requirements, including those from the focus groups. Then, all user requirements were
prioritized based on several aspects, such as priority in the focus groups and feasibility
of implementation. This resulted in a categorization of all user requirements into one of

Sustainability 2022,14, 4151 10 of 17
three categories: high, medium, and low priority. User requirements of high priority were
considered as obligatory for the implementation of the assistance system, while those of
medium priority were not must-haves but should be implemented if feasible. The user
requirements of low priority were only seen as optional add-ons.
In the final phase of the user requirement analysis, personas and scenarios [
55
] were
created based on the focus groups and the complete list of user requirements. More
precisely, six personas were created representing relevant public transport user groups with
their specific needs as identified in the previous phases of the user requirement analysis.
The six personas are presented in Table 2. Moreover, personas for the driver and the control
center operator were created. For each persona, two scenarios were derived describing
exemplary use cases and user requirements in context as well as how the persona uses the
system successfully. The objective of using the persona and scenario approach was, thus, to
make the user requirements more usable and easily applicable throughout the process of
prototype development and implementation and avoid them being forgotten throughout
the process [56].
Table 2. Personas of public transport user groups.
Name Depiction Age Occupational
Status
Residential
Area
Public
Transport Usage
User
Interfaces Special Needs
Philipp
Wagner
Sustainability 2022, 14, x FOR PEER REVIEW 10 of 18
for each service ordered by priority depending on how many times certain aspects were
mentioned and how the participants prioritized them.
To complement the list of user requirements with a further perspective, requirements
were additionally collected systematically within the project consortium. Everybody was
asked to brainstorm user requirements for given contexts of use and the relevant user
interfaces. All the responses were collected and consolidated to create a composite list of
user requirements, including those from the focus groups. Then, all user requirements
were prioritized based on several aspects, such as priority in the focus groups and feasi-
bility of implementation. This resulted in a categorization of all user requirements into
one of three categories: high, medium, and low priority. User requirements of high prior-
ity were considered as obligatory for the implementation of the assistance system, while
those of medium priority were not must-haves but should be implemented if feasible. The
user requirements of low priority were only seen as optional add-ons.
In the final phase of the user requirement analysis, personas and scenarios [55] were
created based on the focus groups and the complete list of user requirements. More pre-
cisely, six personas were created representing relevant public transport user groups with
their specific needs as identified in the previous phases of the user requirement analysis.
The six personas are presented in Table 2. Moreover, personas for the driver and the con-
trol center operator were created. For each persona, two scenarios were derived describ-
ing exemplary use cases and user requirements in context as well as how the persona uses
the system successfully. The objective of using the persona and scenario approach was,
thus, to make the user requirements more usable and easily applicable throughout the
process of prototype development and implementation and avoid them being forgotten
throughout the process [56].
Table 2. Personas of public transport user groups.
Name Depiction Age
Occupational
Status
Residential
Area
Public Transport
Usage
User
Interfaces
Special
Needs
Philipp
Wagner
26 student city several times a
week smartphone
requires
multipurpose
area for his bike
occasionally
Nadia
Karimi
37 employed city daily smartphone none
Martin
Seifert
55 employed rural district occasionally
website,
DPI displays, in-
vehicle
displays and ter-
minals
none
Frieda
Hofmann
82 retired rural district
several times a
month
DPI displays, in-
vehicle
displays and ter-
minals
requires a seat
26 student city several times a
week smartphone
requires
multipurpose
area for his bike
occasionally
Nadia
Karimi
Sustainability 2022, 14, x FOR PEER REVIEW 10 of 18
for each service ordered by priority depending on how many times certain aspects were
mentioned and how the participants prioritized them.
To complement the list of user requirements with a further perspective, requirements
were additionally collected systematically within the project consortium. Everybody was
asked to brainstorm user requirements for given contexts of use and the relevant user
interfaces. All the responses were collected and consolidated to create a composite list of
user requirements, including those from the focus groups. Then, all user requirements
were prioritized based on several aspects, such as priority in the focus groups and feasi-
bility of implementation. This resulted in a categorization of all user requirements into
one of three categories: high, medium, and low priority. User requirements of high prior-
ity were considered as obligatory for the implementation of the assistance system, while
those of medium priority were not must-haves but should be implemented if feasible. The
user requirements of low priority were only seen as optional add-ons.
In the final phase of the user requirement analysis, personas and scenarios [55] were
created based on the focus groups and the complete list of user requirements. More pre-
cisely, six personas were created representing relevant public transport user groups with
their specific needs as identified in the previous phases of the user requirement analysis.
The six personas are presented in Table 2. Moreover, personas for the driver and the con-
trol center operator were created. For each persona, two scenarios were derived describ-
ing exemplary use cases and user requirements in context as well as how the persona uses
the system successfully. The objective of using the persona and scenario approach was,
thus, to make the user requirements more usable and easily applicable throughout the
process of prototype development and implementation and avoid them being forgotten
throughout the process [56].
Table 2. Personas of public transport user groups.
Name Depiction Age
Occupational
Status
Residential
Area
Public Transport
Usage
User
Interfaces
Special
Needs
Philipp
Wagner
26 student city several times a
week smartphone
requires
multipurpose
area for his bike
occasionally
Nadia
Karimi
37 employed city daily smartphone none
Martin
Seifert
55 employed rural district occasionally
website,
DPI displays, in-
vehicle
displays and ter-
minals
none
Frieda
Hofmann
82 retired rural district
several times a
month
DPI displays, in-
vehicle
displays and ter-
minals
requires a seat
37 employed city daily smartphone none
Martin
Seifert
Sustainability 2022, 14, x FOR PEER REVIEW 10 of 18
for each service ordered by priority depending on how many times certain aspects were
mentioned and how the participants prioritized them.
To complement the list of user requirements with a further perspective, requirements
were additionally collected systematically within the project consortium. Everybody was
asked to brainstorm user requirements for given contexts of use and the relevant user
interfaces. All the responses were collected and consolidated to create a composite list of
user requirements, including those from the focus groups. Then, all user requirements
were prioritized based on several aspects, such as priority in the focus groups and feasi-
bility of implementation. This resulted in a categorization of all user requirements into
one of three categories: high, medium, and low priority. User requirements of high prior-
ity were considered as obligatory for the implementation of the assistance system, while
those of medium priority were not must-haves but should be implemented if feasible. The
user requirements of low priority were only seen as optional add-ons.
In the final phase of the user requirement analysis, personas and scenarios [55] were
created based on the focus groups and the complete list of user requirements. More pre-
cisely, six personas were created representing relevant public transport user groups with
their specific needs as identified in the previous phases of the user requirement analysis.
The six personas are presented in Table 2. Moreover, personas for the driver and the con-
trol center operator were created. For each persona, two scenarios were derived describ-
ing exemplary use cases and user requirements in context as well as how the persona uses
the system successfully. The objective of using the persona and scenario approach was,
thus, to make the user requirements more usable and easily applicable throughout the
process of prototype development and implementation and avoid them being forgotten
throughout the process [56].
Table 2. Personas of public transport user groups.
Name Depiction Age
Occupational
Status
Residential
Area
Public Transport
Usage
User
Interfaces
Special
Needs
Philipp
Wagner
26 student city several times a
week smartphone
requires
multipurpose
area for his bike
occasionally
Nadia
Karimi
37 employed city daily smartphone none
Martin
Seifert
55 employed rural district occasionally
website,
DPI displays, in-
vehicle
displays and ter-
minals
none
Frieda
Hofmann
82 retired rural district
several times a
month
DPI displays, in-
vehicle
displays and ter-
minals
requires a seat
55 employed rural district occasionally
website, DPI
displays,
in-vehicle
displays and
terminals
none
Frieda
Hofmann
Sustainability 2022, 14, x FOR PEER REVIEW 10 of 18
for each service ordered by priority depending on how many times certain aspects were
mentioned and how the participants prioritized them.
To complement the list of user requirements with a further perspective, requirements
were additionally collected systematically within the project consortium. Everybody was
asked to brainstorm user requirements for given contexts of use and the relevant user
interfaces. All the responses were collected and consolidated to create a composite list of
user requirements, including those from the focus groups. Then, all user requirements
were prioritized based on several aspects, such as priority in the focus groups and feasi-
bility of implementation. This resulted in a categorization of all user requirements into
one of three categories: high, medium, and low priority. User requirements of high prior-
ity were considered as obligatory for the implementation of the assistance system, while
those of medium priority were not must-haves but should be implemented if feasible. The
user requirements of low priority were only seen as optional add-ons.
In the final phase of the user requirement analysis, personas and scenarios [55] were
created based on the focus groups and the complete list of user requirements. More pre-
cisely, six personas were created representing relevant public transport user groups with
their specific needs as identified in the previous phases of the user requirement analysis.
The six personas are presented in Table 2. Moreover, personas for the driver and the con-
trol center operator were created. For each persona, two scenarios were derived describ-
ing exemplary use cases and user requirements in context as well as how the persona uses
the system successfully. The objective of using the persona and scenario approach was,
thus, to make the user requirements more usable and easily applicable throughout the
process of prototype development and implementation and avoid them being forgotten
throughout the process [56].
Table 2. Personas of public transport user groups.
Name Depiction Age
Occupational
Status
Residential
Area
Public Transport
Usage
User
Interfaces
Special
Needs
Philipp
Wagner
26 student city several times a
week smartphone
requires
multipurpose
area for his bike
occasionally
Nadia
Karimi
37 employed city daily smartphone none
Martin
Seifert
55 employed rural district occasionally
website,
DPI displays, in-
vehicle
displays and ter-
minals
none
Frieda
Hofmann
82 retired rural district
several times a
month
DPI displays, in-
vehicle
displays and ter-
minals
requires a seat
82 retired rural district several times a
month
DPI displays,
in-vehicle
displays and
terminals
requires a seat
Karla
Schneider
Sustainability 2022, 14, x FOR PEER REVIEW 11 of 18
Karla
Schneider
42 employed city daily
smartphone,
DPI displays,
public displays
requires
accessibility and
multipurpose
area due to
wheelchair
Manfred
Kowalski
63 employed city daily smartphone,
DPI displays
requires
accessibility due
to blindness
5. Prototypical Implementation and Laboratory Studies
As mentioned previously, the services occupancy rate, TCMS system, and delivery
service presented in Section 2 will first be implemented as prototypes on the user inter-
faces presented in Section 3 and evaluated in laboratory studies. The prototypes designed
are based on the personas and scenarios described above. Table 3 summarizes which ser-
vices are to be implemented as prototypes for each user interface and shows what the
evaluation of the respective user interface in the laboratory studies should cover. This
evaluation should also ensure that all the user requirements are met.
Table 3. Implementation and evaluation of the services for the respective user interfaces.
User
Interface
Assistance System Services Prototype Evaluation
Occupancy
Rate
TCMS
System
Delivery
Service Usability Technology
Acceptance
Recognizability
and Interpretation
smartphone,
smartwatch,
smart glasses
✓ ✓ ✓ ✓
DPI display ✓
✓ ✓
in-vehicle
display ✓
✓ ✓
in-vehicle
terminal ✓ ✓ ✓
public
display ✓ ✓ ✓ ✓
on-board
computer ✓ ✓
control
center ✓ ✓ ✓ ✓
For the prototype evaluation in laboratory studies, the user interfaces were first inte-
grated into a laboratory environment, the mobility laboratory, as shown in Figure 3. This
includes exterior and interior vehicle displays, an in-vehicle terminal, a DPI display, a
tram simulator including two types of on-board computers, a mobile touch screen used
both as a terminal and as a public display, and a control center workstation. Furthermore,
smartphone, smartwatch, and smart glasses can be used in the laboratory. In addition to
the mobility laboratory, a cave automatic virtual environment (CAVE) and a robotic la-
boratory are used for further evaluations.
42 employed city daily
smartphone,
DPI displays,
public displays
requires
accessibility and
multipurpose
area due to
wheelchair
Manfred
Kowalski
Sustainability 2022, 14, x FOR PEER REVIEW 11 of 18
Karla
Schneider
42 employed city daily
smartphone,
DPI displays,
public displays
requires
accessibility and
multipurpose
area due to
wheelchair
Manfred
Kowalski
63 employed city daily smartphone,
DPI displays
requires
accessibility due
to blindness
5. Prototypical Implementation and Laboratory Studies
As mentioned previously, the services occupancy rate, TCMS system, and delivery
service presented in Section 2 will first be implemented as prototypes on the user inter-
faces presented in Section 3 and evaluated in laboratory studies. The prototypes designed
are based on the personas and scenarios described above. Table 3 summarizes which ser-
vices are to be implemented as prototypes for each user interface and shows what the
evaluation of the respective user interface in the laboratory studies should cover. This
evaluation should also ensure that all the user requirements are met.
Table 3. Implementation and evaluation of the services for the respective user interfaces.
User
Interface
Assistance System Services Prototype Evaluation
Occupancy
Rate
TCMS
System
Delivery
Service Usability Technology
Acceptance
Recognizability
and Interpretation
smartphone,
smartwatch,
smart glasses
✓ ✓ ✓ ✓
DPI display ✓
✓ ✓
in-vehicle
display ✓
✓ ✓
in-vehicle
terminal ✓ ✓ ✓
public
display ✓ ✓ ✓ ✓
on-board
computer ✓ ✓
control
center ✓ ✓ ✓ ✓
For the prototype evaluation in laboratory studies, the user interfaces were first inte-
grated into a laboratory environment, the mobility laboratory, as shown in Figure 3. This
includes exterior and interior vehicle displays, an in-vehicle terminal, a DPI display, a
tram simulator including two types of on-board computers, a mobile touch screen used
both as a terminal and as a public display, and a control center workstation. Furthermore,
smartphone, smartwatch, and smart glasses can be used in the laboratory. In addition to
the mobility laboratory, a cave automatic virtual environment (CAVE) and a robotic la-
boratory are used for further evaluations.
63 employed city daily smartphone,
DPI displays
requires
accessibility due
to blindness
5. Prototypical Implementation and Laboratory Studies
As mentioned previously, the services occupancy rate, TCMS system, and delivery
service presented in Section 2will first be implemented as prototypes on the user interfaces
presented in Section 3and evaluated in laboratory studies. The prototypes designed are

Sustainability 2022,14, 4151 11 of 17
based on the personas and scenarios described above. Table 3summarizes which services
are to be implemented as prototypes for each user interface and shows what the evaluation
of the respective user interface in the laboratory studies should cover. This evaluation
should also ensure that all the user requirements are met.
Table 3. Implementation and evaluation of the services for the respective user interfaces.
User
Interface
Assistance System Services Prototype Evaluation
Occupancy
Rate
TCMS
System
Delivery
Service Usability Technology
Acceptance
Recognizability
and Interpretation
smartphone, smartwatch,
smart glasses    
DPI display   
in-vehicle display   
in-vehicle terminal   
public display    
on-board computer  
control center    
For the prototype evaluation in laboratory studies, the user interfaces were first
integrated into a laboratory environment, the mobility laboratory, as shown in Figure 3.
This includes exterior and interior vehicle displays, an in-vehicle terminal, a DPI display, a
tram simulator including two types of on-board computers, a mobile touch screen used
both as a terminal and as a public display, and a control center workstation. Furthermore,
smartphone, smartwatch, and smart glasses can be used in the laboratory. In addition to the
mobility laboratory, a cave automatic virtual environment (CAVE) and a robotic laboratory
are used for further evaluations.
Sustainability 2022, 14, x FOR PEER REVIEW 12 of 18
Figure 3. Mobility laboratory setup.
The digital prototypes will be implemented as click prototypes for user interfaces
allowing interaction, such as smartphones, in-vehicle terminals, and public displays. Pro-
totypes for non-interactive interfaces such as the DPI and the in-vehicle display will be
implemented as a sequence of images. Questionnaires are created according to the char-
acteristics to be evaluated, such as usability, technology acceptance, or recognizability and
interpretation. User interfaces for passengers will be evaluated by test persons in the role
of passengers with a scenario-based approach simulated in the laboratory. User interfaces
for public transport operators will be evaluated via expert interviews.
Several laboratory evaluations of assistance system components have already been
completed. In a study, the display of the occupancy of multipurpose areas on the DPI
display was examined concerning speed and reliability of interpretation [57]. The study
also investigated the intent of prospective use. Furthermore, a sign-production method
based on Howell and Fuchs [58] was applied to create symbols for occupancy level and
transfer connection request. The results will be used in the various user interfaces after
further evaluation. Prototype evaluations for the smartwatch and for the in-vehicle termi-
nal also took place, and a concept for displaying information on smart glasses was evalu-
ated [59]. Moreover, a study was conducted in the CAVE to investigate trust in the assis-
tance system with a scenario-based approach [60].
Further studies and evaluations will follow as the project progresses. According to
the results from the laboratory studies, the prototypes will be adjusted if necessary. Rec-
ommendations will be derived and applied to existing real systems according to the tech-
nical framework conditions and evaluated in a one-year field study.
6. Evaluation in One-Year Field Study
In the final phase of the project, the assistance system will be evaluated more holisti-
cally by means of a one-year field study on selected lines of the NVV in Kassel. Aspects
such as traffic effects, acceptance, and usability will be investigated. In addition to the
actual purpose of evaluating the developed services, the field study aims to derive basic
scientific findings to ultimately translate into recommended actions.
Figure 3. Mobility laboratory setup.
The digital prototypes will be implemented as click prototypes for user interfaces
allowing interaction, such as smartphones, in-vehicle terminals, and public displays. Pro-

Sustainability 2022,14, 4151 12 of 17
totypes for non-interactive interfaces such as the DPI and the in-vehicle display will be
implemented as a sequence of images. Questionnaires are created according to the charac-
teristics to be evaluated, such as usability, technology acceptance, or recognizability and
interpretation. User interfaces for passengers will be evaluated by test persons in the role
of passengers with a scenario-based approach simulated in the laboratory. User interfaces
for public transport operators will be evaluated via expert interviews.
Several laboratory evaluations of assistance system components have already been
completed. In a study, the display of the occupancy of multipurpose areas on the DPI
display was examined concerning speed and reliability of interpretation [
57
]. The study also
investigated the intent of prospective use. Furthermore, a sign-production method based
on Howell and Fuchs [
58
] was applied to create symbols for occupancy level and transfer
connection request. The results will be used in the various user interfaces after further
evaluation. Prototype evaluations for the smartwatch and for the in-vehicle terminal also
took place, and a concept for displaying information on smart glasses was evaluated [
59
].
Moreover, a study was conducted in the CAVE to investigate trust in the assistance system
with a scenario-based approach [60].
Further studies and evaluations will follow as the project progresses. According
to the results from the laboratory studies, the prototypes will be adjusted if necessary.
Recommendations will be derived and applied to existing real systems according to the
technical framework conditions and evaluated in a one-year field study.
6. Evaluation in One-Year Field Study
In the final phase of the project, the assistance system will be evaluated more holisti-
cally by means of a one-year field study on selected lines of the NVV in Kassel. Aspects
such as traffic effects, acceptance, and usability will be investigated. In addition to the
actual purpose of evaluating the developed services, the field study aims to derive basic
scientific findings to ultimately translate into recommended actions.
The one-year field study has the advantage of testing and evaluating the reliability,
practicality, and usability as well as acceptance and behavioral changes as a result of the
assistance system on real passengers. An evaluation going beyond a sample of test persons
requires a high degree of awareness and a high frequency of use. For this reason, the
introduction of each of the three services will be publicly communicated and advertised.
Subsequently, the usage frequencies of the three services will be analyzed over the entire
period of the field study. In addition, the quality of the occupancy rate will be specifically
tested based on actual occupancy. For the connection request and the delivery service,
usage data will serve to determine specifically where, for which lines, in which situations,
and how frequently the services are used.
As already mentioned, the analysis of traffic effects of the three services represents a
focal point in the evaluation. For this purpose, a multi-layered survey design is developed,
characterized by a mix of methods. This allows determining the travel behavior concerning
the frequency of choosing public transport in the NVV area, and in particular, with regard
to the connection choice before and after the introduction of the three services. Based on
the mix of methods, different groups of people are addressed, and various characteristics
can be validly surveyed. In the following, further details on the field study are provided
for each assistance system service.
6.1. Occupancy Rate
Firstly, an annual online panel survey of 3000 randomly selected citizens of Kassel
is used to gain representative information on public transport users’ and non-users’ as-
sessment of the passenger load of vehicles. By conducting the survey three times with the
same sample, it is possible to analyze developments in the respondents’ assessment before,
during, and after completion of the field study.
Secondly, a passenger survey will be conducted to obtain data on awareness, use of
the service, and adjustments in travel behavior (including choice of connections) as a result

Sustainability 2022,14, 4151 13 of 17
of available information on expected occupancy levels. The quantitative survey aims to
find representative answers to the following research questions with a sample of about
1000 passengers:
•
How often do passengers pay attention to the occupancy rate when
querying connections?
•For what reasons is the occupancy rate (not) of interest to passengers?
•
Do passengers choose alternative connections based on the information about the
expected occupancy rate?
•
What are passengers most likely to accept in exchange for a low occupancy rate: a
longer wait for the next connection, a longer trip duration, or more transfers?
•
Based on the occupancy rate, do passengers use public transport more frequently,
equally frequently, or less frequently?
•How useful, reliable, and understandable do passengers find the service?
•
Do people with wheelchairs, walkers, strollers, bicycles, or similar use public transport
more frequently, equally frequently, or less frequently based on the occupancy rate for
the multipurpose areas?
The surveys will take place at the earliest six months after the implementation of the
services. For this purpose, questionnaires will be designed and applied depending on the
remaining travel time of the respondent. The survey will be carried out by survey staff
interviewing passengers orally in buses and trams of the NVV after a random selection
and recording the answers digitally on tablet computers. To consider the users of the
multipurpose areas, specifically passengers with wheelchairs, walkers, baby carriages,
bicycles, pedal scooters, etc., will be surveyed. In addition to the passenger survey, an online
survey with similar content will be distributed via the NVV app in order to increase the
willingness to participate across the various survey formats and to increase the
sample size.
When evaluating the results of the occupancy rate, the influence of the COVID 19
pandemic must be taken into account. Contact reductions, distance regulations between
people, and a lack of necessities of ways have temporarily led to a strongly reduced
passenger demand [61].
6.2. TCMS System
Observation and survey data will be collected to evaluate the TCMS system. The
success rate of planned connections before the field phase is compared with the success
rate of requested connections during the field phase. This way, the effects of the TCMS
system on the planning reliability for passengers and the reliability of public transport in
the NVV area can be assessed. Furthermore, a standardized online survey via the NVV app
will be used to determine whether and to what extent the TCMS system has an impact on
the passengers’ travel behavior. The survey will be linked to transfer connection requests
to be able to relate the answers to the requested transfer between two lines and to generate
differentiated findings. The survey will be conducted throughout the entire field study. In
parallel, operational effects of the TCMS system will be evaluated through an analysis of
logged data on delays, shortened breaks, and turning times as well as on interventions in
ongoing operations.
Based on the selected evaluation methods, the following research questions will
be answered:
•Does the TCMS system generate additional passenger demand?
•In which situations do passengers use the TCMS system?
•What is the average time interval between the connection request and the transfer?
•
To what extent does the TCMS system increase the reliability of public transport
from the passengers’ perspective? What role does information about alternative
connections play?
•How useful and understandable do passengers find the TCMS system?

Sustainability 2022,14, 4151 14 of 17
6.3. Delivery Service
The evaluation of the delivery service in terms of traffic effects will be based on
user surveys during the field study to determine whether the service makes the use of
public transport for shopping more attractive. Customers will be asked to voluntarily
participate in an online survey based on a standardized procedure at the cash registers
of the participating stores in Kassel after submitting their delivery requests. Another
aspect to be evaluated is the use of small electric vehicles for the delivery of goods to the
users of the delivery service and for the distribution of goods to the stores as part of the
city logistics. A before-and-after analysis of the mode of transport choices of customers
and CEP service providers will be used. This will provide information on whether the
developed combination of services and infrastructure—the delivery service and the parcel
stations distributed at several locations in Kassel (see Section 2.3)—leads to an overall
more environmentally friendly mobility for the bundled delivery and pick-up of goods,
especially in the city center.
The following research questions will be assessed as part of the evaluation of the
delivery service from a traffic and usability perspective:
•Does the delivery service lead to an increased use of public transport for shopping?
•What is the modal split of delivery service users?
•How would customers have transported the goods without the delivery service?
•
Does the combination of environmentally friendly transport and delivery service
generate less traffic overall and is it more sustainable than car trips?
•
How useful, reliable, and understandable do users find the delivery service and
parcel stations?
7. Conclusions
In this paper, we presented a concept for a passenger assistance system aiming to
increase the attractiveness of local public transport and promote sustainable travel behavior.
The concept has its limitations that need to be discussed. One limiting factor is the local
limitation of the assistance system to the city and region of Kassel, Germany. Whether and
how the system can be implemented in other cities or countries must be investigated further.
The results of the upcoming field study will provide further implications regarding the
implementation of the concept in Kassel and other cities. However, the ongoing pandemic
with changing regulations for public transport may have an impact on the study results.
The constantly changing pandemic situation also poses a challenge to the concepts of the
forecasting models because demand was and still is subject to strong variability. Historical
data, therefore, offer only limited explanatory power for future demand. In the course
of the forecast conception, the integration of further possible data sources was examined
but eventually dropped. These data sources included, for example, query log data, event
data, and data from weight sensors and rain sensors of the vehicles. The integration of
these (or other additional) data sources might improve the accuracy of the forecasting
models. Hurdles and limitations concerning data sources encountered in this project
include data access and ownership, data maintenance, and safety concerns (in the case of
brake sensor data).
Nevertheless, the assistance system with its novel services has the potential to make
local public transport more attractive. Based on the literature review and a preliminary
survey, a high demand for such a system was revealed. Particularly crowded vehicles,
missed connections, and inconveniences of transporting shopping bags or luggage were
identified as barriers to the use of public transport. The presented assistance system concept
tackles these issues with the services occupancy rate, TCMS system, and delivery service.
The three services were presented in more detail and their conceptual implementation
into the respective user interfaces was described. For the actual prototypical implemen-
tation, a user requirement analysis was conducted. This analysis supported that public
transport passengers want, above all, secure connections and reliable information about
whether they will reach their connection and what alternative connection would otherwise

Sustainability 2022,14, 4151 15 of 17
be available. Therefore, the connection request function is particularly important for users.
For mobility-impaired people, it is also important to know whether they can find a free
seat in the vehicle or whether the multipurpose areas are occupied.
Due to the complexity of the assistance system and the different interfaces involved, it
is necessary to evaluate the system thoroughly before its implementation. Thus, prototypes
are first evaluated in a laboratory setting and based on the results implemented for a
one-year field study. This has the advantage of testing and evaluating the reliability,
practicability, and usability as well as the acceptance and behavioral changes caused by
the assistance system on real passengers. For the occupancy rate, this will take the form
of a panel survey. Observation and survey data will be collected during the entire field
study to evaluate the TCMS system. To evaluate the delivery service in terms of traffic
impacts, user surveys will be conducted during the field study to determine whether the
service makes it more attractive to use public transport for shopping. These evaluations
will provide insights into the success of the passenger assistance system and conclusions
regarding recommended actions.
Author Contributions:
Conceptualization, L.S. and C.S.; writing—original draft preparation, A.K.F.,
J.H., S.E.K., F.L., D.L., S.S. and F.W.; writing—review and editing, all authors; supervision, L.S. and
C.S.; funding acquisition, L.S. and C.S. All authors have read and agreed to the published version of
the manuscript.
Funding:
This research was funded by the German Federal Ministry of Education and Research
(funding code 16SV8241).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Bundes-Klimaschutzgesetz: KSG. 2019. Available online: https://www.gesetze-im-internet.de/ksg/BJNR251310019.html (accessed
on 28 February 2022).
2.
Anagnostopoulou, E.; Bothos, E.; Magoutas, B.; Schrammel, J.; Mentzas, G. Persuasive Technologies for Sustainable Mobility:
State of the Art and Emerging Trends. Sustainability 2018,10, 2128. [CrossRef]
3.
Kuhnimhof, T.; Nobis, C. Mobilität in Deutschland—MiD Ergebnisbericht: Studie von Infas, DLR, IVT und Infas 360 im Auftrag
des Bundesministers für Verkehr und Digitale Infrastruktur FE-Nr. 70.904/15, Bonn, Berlin. 2018. Available online: https:
//www.bmvi.de/SharedDocs/DE/Anlage/G/mid-ergebnisbericht.pdf?__blob=publicationFile (accessed on
18 February 2022).
4.
Aamaas, B.; Borken-Kleefeld, J.; Peters, G.P. The climate impact of travel behavior: A German case study with illustrative
mitigation options. Environ. Sci. Policy 2013,33, 273–282. [CrossRef]
5.
Møller, B.; Thøgersen, J. Car use habits: An obstacle to the use of public transportation? In Road Pricing, the Economy and the
Environment; Jensen-Butler, C., Sloth, B., Larsen, M.M., Madsen, B., Nielsen, O.A., Eds.; Springer: Berlin/Heidelberg, Germany,
2008; pp. 301–313, ISBN 978-3-540-77149-4.
6.
Aarts, H.; Verplanken, B.; van Knippenberg, A. Habit and information use in travel mode choices. Acta Psychol.
1997
,96, 1–14.
[CrossRef]
7.
Verplanken, B.; Aarts, H.; Knippenberg, A.; Knippenberg, C. Attitude versus general habit: Antecedents of travel mode choice. J.
Appl. Soc. Psychol. 1994,24, 285–300. [CrossRef]
8.
Thøgersen, J.; Møller, B. Breaking car use habits: The effectiveness of a free one-month travelcard. Transportation
2008
,35, 329–345.
[CrossRef]
9.
Di Dio, S.; Massa, F.; Nucara, A.; Peri, G.; Rizzo, G.; Schillaci, D. Pursuing softer urban mobility behaviors through game-based
apps. Heliyon 2020,6, e03930. [CrossRef]
10.
Ferron, M.; Loria, E.; Marconi, A.; Massa, P. Play&Go, an urban game promoting behaviour change for sustainable mobility.
Interact. Des. Archit. 2019,40, 24–45.
11.
Kelpin, R.; Giesel, F.; Heinrichs, M. Streetlife Field Trials—Applied gamification approaches as a key to more sustainable mobility
behaviour. In Proceedings of the 44th European Transport Conference, Barcelona, Spain, 5–7 October 2016.
12.
Kazhamiakin, R.; Marconi, A.; Perillo, M.; Pistore, M.; Piras, L.; Avesani, F.; Perri, N.; Valetto, G. Using gamification to incentivize
sustainable urban mobility. In Proceedings of the IEEE International Smart Cities Conference (ISC2), Guadalajara, Mexico,
25–28 October 2015; pp. 1–6.

Sustainability 2022,14, 4151 16 of 17
13.
Gabrielli, S.; Maimone, R. Digital interventions for sustainable urban mobility. In Proceedings of the UbiComp ‘13: 2013 ACM
Conference on Pervasive and Ubiquitous Computing Adjunct Publication, Zurich, Switzerland, 8–12 September 2013; ACM: New
York, NY, USA, 2013; pp. 119–122, ISBN 9781450322157.
14.
Holleis, P.; Luther, M.; Broll, G.; Cao, H.; Koolwaaij, J.; Peddemors, A.; Ebben, P.; Wibbels, M.; Jacobs, K.; Raaphorst, S. TRIPZOOM:
A system to motivate sustainable urban mobility. In Proceedings of the SMART 2012: The First International Conference on Smart
Systems, Devices and Technologies, Stuttgart, Germany, 27 May–1 June 2012; pp. 101–104.
15.
Menendez, M.; Ambühl, L. Implementing design and operational measures for sustainable mobility: Lessons from Zurich.
Sustainability 2022,14, 625. [CrossRef]
16.
Kenyon, S.; Lyons, G. The value of integrated multimodal traveller information and its potential contribution to modal change.
Transp. Res. F Traffic Psychol. Behav. 2003,6, 1–21. [CrossRef]
17.
Lopez-Carreiro, I.; Monzon, A.; Lopez, E.; Lopez-Lambas, M.E. Urban mobility in the digital era: An exploration of travellers’
expectations of MaaS mobile-technologies. Technol. Soc. 2020,63, 101392. [CrossRef]
18.
Karlsson, I.C.M.; Mukhtar-Landgren, D.; Smith, G.; Koglin, T.; Kronsell, A.; Lund, E.; Sarasini, S.; Sochor, J. Development and
implementation of Mobility-as-a-Service—A qualitative study of barriers and enabling factors. Transp. Res. A Policy Pract.
2020
,
131, 283–295. [CrossRef]
19.
Casquero, D.; Monzon, A.; García, M.; Martínez, O. Key elements of mobility apps for improving urban travel patterns: A
literature review. Future Transp. 2022,2, 1–23. [CrossRef]
20.
Bian, J.; Li, W.; Zhong, S.; Lee, C.; Foster, M.; Ye, X. The end-user benefits of smartphone transit apps: A systematic literature
review. Transp. Rev. 2022,42, 82–101. [CrossRef]
21.
Lübke, C.; Hanke, S.; Weimar, M. Barrieren beim Umstieg vom Individualverkehr auf den öffentlichen Personennahverkehr: Ein
Mobilitätsexperiment zum Pendleralltag im Ruhrgebiet. In Making Connected Mobility Work; Proff, H., Ed.; Springer: Wiesbaden,
Germany, 2021; pp. 371–379, ISBN 978-3-658-32265-6.
22.
Ibrahim, M.F. Car ownership and attitudes towards transport modes for shopping purposes in Singapore. Transportation
2003
,30,
435–457. [CrossRef]
23.
Hine, J.; Scott, J. Seamless, accessible travel: Users’ views of the public transport journey and interchange. Transp. Policy
2000
,7,
217–226. [CrossRef]
24.
Aarhaug, J.; Elvebakk, B. The impact of universally accessible public transport—A before and after study. Transp. Policy
2015
,44,
143–150. [CrossRef]
25.
Rietveld, P.; Bruinsma, F.R.; van Vuuren, D.J. Coping with unreliability in public transport chains: A case study for Netherlands.
Transp. Res. A Policy Pract. 2001,35, 539–559. [CrossRef]
26.
Tseng, Y.-Y.; Knockaert, J.; Verhoef, E.T. A revealed-preference study of behavioural impacts of real-time traffic information.
Transp. Res. C Emerg. Technol. 2013,30, 196–209. [CrossRef]
27.
Romero, C.; Monzón, A.; Alonso, A.; Julio, R. Added value of a customized transit app for metropolitan bus trips. Transp. Res.
Proc. 2020,47, 513–520. [CrossRef]
28.
Abdullah, M.; Ali, N.; Javid, M.A.; Dias, C.; Campisi, T. Public transport versus solo travel mode choices during the COVID-19
pandemic: Self-reported evidence from a developing country. J. Transp. Eng. 2021,5, 100078. [CrossRef]
29.
Abdullah, M.; Ali, N.; Dias, C.; Campisi, T.; Javid, M.A. Exploring the Traveler’s Intentions to Use Public Transport during the
COVID-19 Pandemic While Complying with Precautionary Measures. Appl. Sci. 2021,11, 3630. [CrossRef]
30.
Gkiotsalitis, K.; Cats, O. Public transport planning adaption under the COVID-19 pandemic crisis: Literature review of research
needs and directions. Transp. Rev. 2021,41, 374–392. [CrossRef]
31.
Saif, M.A.; Zefreh, M.M.; Torok, A. Public Transport Accessibility: A Literature Review. Period. Polytech. Transp. Eng.
2018
,47,
36–43. [CrossRef]
32.
Martens, J.; Obenland, W. Die Agenda 2030: Globale Zukunftsziele für Nachhaltige Entwicklung, 2nd ed.; Global Policy Forum:
Bonn/Osnabrück, Germany, 2017; ISBN 978-3-943126-35-8.
33.
Barthel, D.; Land, S.; Lopez-Hernandez, D.; Koch, T.; Machatsch, K.; Mante, C.; Radermacher, B.; Seyfried, F.; Tietgens, K.
Auslastungsinformationen in der Fahrgastkommunikation: Ein Überblick über Aktuelle Branchenweite Aktivitäten; VDV-Mitteilung 7052;
Verband Deutscher Verkehrsunternehmen: Köln, Germany, 2021.
34. Ribeiro, P.; Dias, G.; Pereira, P. Transport systems and mobility for smart cities. Appl. Syst. Innov. 2021,4, 61. [CrossRef]
35.
Elias, W.; Shiftan, Y. The influence of individual’s risk perception and attitudes on travel behavior. Transp. Res. A Policy Pract.
2012,46, 1241–1251. [CrossRef]
36.
Umweltbundesamt. Umweltbelastungen Durch Verkehr. Available online: https://www.umweltbundesamt.de/daten/verkehr/
umweltbelastungen-durch-verkehr#undefined (accessed on 17 March 2022).
37.
Klingauf, A.; Hegenberg, J.; Lambrecht, F.; Bieland, D.; Schmidt, L.; Sommer, C. Nutzeranforderungen an ein Assistenzsystem für
den ÖPNV. In Proceedings of the Arbeit Interdisziplinär Analysieren—Bewerten—Gestalten, 65. Kongress der Gesellschaft für
Arbeitswissenschaft, Dresden, Germany, 27 February–1 March 2019; Gesellschaft für Arbeitswissenschaft e. V., Ed.; GfA-Press:
Dortmund, Germany, 2019.
38.
Arabghalizi, T.; Labrinidis, A. Data-driven bus crowding prediction models using context-specific features. ACM/IMS Trans. Data
Sci. 2020,1, 1–33. [CrossRef]

Sustainability 2022,14, 4151 17 of 17
39.
Pasini, K.; Khouadjia, M.; Ganansia, F.; Oukhellou, L. Forecasting passenger load in a transit network using data driven models.
In Proceedings of the WCRR 2019, 12th World Congress on Railway Research, Tokyo, Japan, 28 October–1 November 2019.
40.
Jenelius, E. Data-driven bus crowding prediction based on real-time passenger counts and vehicle locations. In Proceedings of the
6th International Conference on Models and Technologies for Intelligent Transportation Systems (MT-ITS2019), Krakow, Poland,
5–7 June 2019.
41.
Heydenrijk-Ottens, L.; Degeler, V.; Luo, D.; van Oort, N.; van Lint, H. Supervised learning: Predicting passenger load in public
transport. In Proceedings of the CASPT Conference on Advanced Systems in Public Transport and TransitData, Brisbane,
Australia, 23–25 July 2018.
42.
Vandewiele, G.; Colpaert, P.; Janssens, O.; van Herwegen, J.; Verborgh, R.; Mannens, E.; Ongenae, F.; de Turck, F. Predicting train
occupancies based on query logs and external data sources. In Proceedings of the WWW ‘17 Companion: 26th International
Conference on World Wide Web Companion, Perth, Australia, 3–7 April 2017; ACM: New York, NY, USA, 2017; pp. 1469–1474,
ISBN 9781450349147.
43.
Vial, C.; Gazeau, V. Load passenger forecasting towards future bus transportation network. J. ICT Stand.
2020
,8, 185–198.
[CrossRef]
44.
Bäumer, M. Ermittlung von Standards für Anforderungsgerechte Datenqualität bei Verkehrserhebungen; Wirtschaftsverlag NW Verlag
für neue Wissenschaft: Bremerhaven, Germany, 2010; ISBN 978-3-86918-075-5.
45.
Ceder, A.; Chowdhury, S.; Taghipouran, N.; Olsen, J. Modelling public-transport users’ behaviour at connection point. Transp.
Policy 2013,27, 112–122. [CrossRef]
46.
Chowdhury, S.; Ceder, A.; Schwalger, B. The effects of travel time and cost savings on commuters’ decision to travel on public
transport routes involving transfers. J. Transp. Geogr. 2015,43, 151–159. [CrossRef]
47.
Schnieder, L. Betriebsplanung Im Öffentlichen Personennahverkehr: Ziele, Methoden, Konzepte; Springer: Berlin/Heidelberg, Germany,
2015; ISBN 978-3-662-46455-7.
48.
Thelen, A. ADAC Umfrage 2017: Nichtnutzung des ÖPNV. 2017. Available online: https://vm.baden-wuerttemberg.de/
fileadmin/redaktion/m-mvi/intern/bilder/VM_Bilder/Innovationskongress/2-ADAC-A-Nichtnutzung_%C3%96PNV.pdf (ac-
cessed on 28 February 2022).
49. Hamburg. Paketstationen an Bahnhaltestellen: Pilotprojekt Gestartet. Available online: https://www.hamburg.de/bus-bahn/
13676748/hamburger-box/ (accessed on 28 February 2022).
50.
Starship. A Revolution in Local Delivery. Available online: https://www.starship.xyz/company/ (accessed on
28 February 2022).
51.
Nuro. Less Driving. More Thriving: We’re on a Mission to Better Everyday Life through Robotics. Available online: https:
//www.nuro.ai/ (accessed on 28 February 2022).
52.
Maguire, M.; Bevan, N. User requirements analysis: A review of supporting methods. In Usability; Hammond, J., Gross, T.,
Wesson, J., Eds.; Springer: Boston, MA, USA, 2002; pp. 133–148, ISBN 978-1-4757-6910-4.
53.
Klose, E.M.; Eis, A.; Hegenberg, J.; Schmidt, L. Nutzerorientierte Anforderungsanalyse für ein adaptiv lernendes Reiseassisten-
zsystem mit Datenbrillen. Z. Arb. Wiss. 2018,72, 3–12. [CrossRef]
54.
Stewart, D.W.; Shamdasani, P.N. Focus Groups: Theory and Practice, 3rd ed.; Sage: Los Angeles, CA, USA, 2015; ISBN 9781452270982.
55. Cooper, A. The Inmates Are Running the Asylum; Sams: Indianapolis, IN, USA, 1999.
56. Guðjónsdóttir, R. Personas and Scenarios in Use. Dissertation; KTH Royal Institute of Technology: Stockholm, Sweden, 2010.
57.
Wehr, F.; Schmidt, L. Evaluation von Icons für LED-basierte Haltestellenanzeiger im öffentlichen Personennahverkehr. In
Proceedings of the Technologie und Bildung in Hybriden Arbeitswelten, 68. Kongress der Gesellschaft für Arbeitswissenschaft,
Magdeburg, Germany, 2–4 March 2022; Gesellschaft für Arbeitswissenschaft e. V., Ed.; GfA-Press: Sankt Augustin, Germany,
2022, in press.
58. Howell, W.C.; Fuchs, A.H. Population stereotypy in code design. Organ. Behav. Hum. Perform. 1968,3, 310–339. [CrossRef]
59.
Faulhaber, A.K.; Hoppe, M.; Schmidt, L. Priority-Dependent Display of Notifications in the Peripheral Field of View of Smart
Glasses. In Proceedings of the 28th IEEE Conference on Virtual Reality and 3D User Interfaces, Christchurch, New Zealand, 12–16
March 2022; IEEE: Piscataway, NJ, USA, 2022, in press.
60.
Faulhaber, A.K.; Ni, I.; Schmidt, L. The effect of explanations on trust in an assistance system for public transport users and the
role of the propensity to trust. In Proceedings of the MuC ‘21: Mensch und Computer 2021, Ingolstadt, Germany, 5–8 September
2021; Schneegass, S., Pfleging, B., Kern, D., Eds.; ACM: New York, NY, USA, 2021; pp. 303–310, ISBN 9781450386456.
61.
Statistisches Bundesamt. Fahrgastzahl im Linienfernverkehr mit Bahnen und Bussen im Jahr 2020 Halbiert: Pressemitteilung Nr. 172 vom
8. April 2021; Statistisches Bundesamt: Wiesbaden, Germany, 2021.