![Plan views and key features of the three bus layout configurations selected for study. Mannequin placement for simulated conditions of low (light grey) and high (both light and dark grey) Passenger Load are also depicted. Table modified from [36].](https://www.researchgate.net/profile/Clive-Dsouza/publication/321041607/figure/fig6/AS:828045170589697@1574432761085/Plan-views-and-key-features-of-the-three-bus-layout-configurations-selected-for-study_Q320.jpg)
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Self-Reported Difficulty and Preferences of Wheeled Mobility Device Users
for Simulated Low-Floor Bus Boarding, Interior Circulation, and
Disembarking
Clive D’Souzaa*, Victor L. Paquetb,c, James A. Lenkerb,d and Edward Steinfeldb,e
a Center for Ergonomics, Department of Industrial and Operations Engineering, University of
Michigan, Ann Arbor, Michigan, USA;
b Center for Inclusive Design and Environmental Access, University at Buffalo, Buffalo, NY,
USA;
c Department of Industrial and Systems Engineering, University at Buffalo, Buffalo, NY, USA;
d Department of Rehabilitation Science, University at Buffalo, Buffalo, NY, USA;
e Department of Architecture, University at Buffalo, Buffalo, NY, USA;
* Corresponding author: Clive D’Souza, Ph.D., Center for Ergonomics, Department of Industrial
and Operations Engineering, G636 IOE, University of Michigan, 1205 Beal Avenue, Ann Arbor,
Michigan 48109-2117 USA; phone: 1-734-763-0542; email: crdsouza@umich.edu ; orcid: 0000-
0003-1652-3001
Word count (main text): 7286.
Self-Reported Difficulty and Preferences of Wheeled Mobility Device Users
for Simulated Low-Floor Bus Boarding, Internal Circulation, and
Disembarking
Background: Low ridership of public transit buses among wheeled mobility device users
suggests the need to identify vehicle design conditions that are either particularly
accommodating or challenging. The objective of this study was to determine the effects of
low -floor bus interior seating configuration and passenger load on wheeled mobility
device user-reported difficulty, overall acceptability, and design preference.
Methods: Forty-eight wheeled mobility users evaluated three interior design layouts at two
levels of passenger load (high vs. low) after simulating boarding and disembarking tasks on
a static full-scale low-floor bus mock-up.
Results: User self-reports of task difficulty, acceptability and design preference were
analysed across the different test conditions. Ramp ascent was the most difficult task for
manual wheelchair users relative to other tasks. The most difficult tasks for users of power
wheelchairs and scooters were related to interior circulation, including moving to the
securement area, entry and positioning in the securement area, and exiting the securement
area. Boarding and disembarking at the rear doorway was significantly more acceptable
and preferred compared to the layouts with front doorways.
Conclusion: Understanding transit usability barriers, perceptions and preferences among
wheeled mobility users is an important consideration for clinicians who recommend
mobility-related device interventions to those who use public transportation.
Keywords: wheelchairs; accessibility; usability; low-floor bus; public transportation;
Introduction
Public transit serves as an important means to social participation and access to health,
employment and recreational activities for many individuals. It is imperative that transit systems
are usable and accessible to the broad diversity of potential users. Substantial advances have
been made in accessible transportation due to implementation of various laws and regulations but
major barriers and impediments still remain.
General problems facing wheeled mobility device users on low-floor buses
Low-floor buses are the most popular type of urban transit bus used in the US [1]. The relatively
low vehicle floor combined with a kneeling feature at stops and electromechanical folding ramps
at the doorways reduces the vertical and horizontal gap between vehicle floor and sidewalk. This
greatly improves the ease of boarding and disembarking [2, 3]. However, current low-floor bus
designs still present safety hazards and usability problems for passengers with mobility
impairments [4]. Inadequate seating, crowding and congestion are among the most frequently
cited complaints by passengers on low-floor buses [3]. Large wheel-well covers that protrude
into the passenger cabin combined with inefficient interior circulation from irregular seating
configurations also contribute to these problems [3, 5] and to a lower seating capacity compared
to high-floor buses.
Wheeled mobility device users in particular experience more difficulties than their
ambulatory counterparts when using low-floor buses due to steep access ramps and limited space
for on-board manoeuvring [2, 4, 5]. These problems also increase the risk of injury under non-
impact conditions such as when boarding and disembarking [6, 7]. As much as 43% of wheeled
mobility device related incidents on public transit occur when the bus is stopped presumably
when boarding and disembarking [8].
Understanding how dimensions and configurations of vehicle interiors affect wheeled
mobility device user access, comfort and safety is critical due to their unique space requirements,
diverse equipment, and high variability of abilities [2, 4]. Bus manufacturers and transit agencies
across the US are obligated to comply with the Americans with Disabilities Act Accessibility
Guidelines and Standards [9, 10] but have some flexibility in their approaches to operationalizing
provisions of the legislation. As a result, low-floor buses vastly differ in interior seating
configurations, door locations and the fare payment system. Design decisions are all interrelated
and influence the size and location of wheeled mobility securement areas and the usability of
path to and from the accessible doorway(s) during bus boarding and disembarking tasks.
The size, weight and manoeuvring characteristics of wheeled mobility devices vary
considerably between device type (e.g., manual wheelchairs, powered wheelchairs and scooters),
make, and model [11, 12]. Both manual and powered wheelchairs offer some customizability to
fit user needs in postural support, comfort, and ease of use (e.g., leg rests and footrests, tilt and
recline) which also impacts space requirements [12, 13]. The choice of drive configuration (i.e.,
front, mid, and rear wheel-drive) and powered seating options influence manoeuvrability of
powered wheelchairs [14]. Scooters typically have a larger turning circle and are less
manoeuvrable than wheelchairs because their configuration and chassis length need to
accommodate the drive controls (e.g., tiller) and foot placement [14, 15, 16]. These devices tend
to be designed and prescribed for outdoor use. They are intended to assist individuals with
limited ambulation and good trunk control and sufficient upper extremity function to control the
steering tiller, but who also lack the upper extremity stamina or range of motion necessary to use
a manual wheelchair. Some users prefer scooters as it may suggest a less debilitating medical
condition compared to requiring a wheelchair. Increasing use of scooters among the growing
older adult population has put greater emphasis on scooter access in public transit systems.
Previous Usability Research on Transit Vehicle Features by Wheeled Mobility Device
Users
A range of methods have been used previously to evaluate designs of transit vehicle interiors by
wheeled mobility device users. Methods used in field studies include first-person observations
[e.g., 17, 18], on-board surveys to query transit riders on perceptions and problems experienced
in the vehicle environment [19], retrospective analysis of incident reports [8], and systematic
audits of a predetermined part of a transit system by an observer [20] or researcher and
participant [21]. More recent studies have relied on reviewing on-board video surveillance
recordings obtained from buses in operation to extract information about the number and
duration of boarding and disembarking by passengers using wheeled mobility devices [e.g., 22],
and to identify safety-critical incidents involving wheeled mobility device users [e.g., 7]. Field
studies are advantageous because they utilize real-world environmental conditions, such as
moving vehicles and passenger interaction, providing reliable information on both system
performance and passenger experience. However, uncontrolled factors such as passenger flow
and crowding can complicate data interpretation. In addition, field studies are constrained by the
vehicles that are in operation, which poses challenges to studying new designs that are not yet in
service.
Some field studies have focused on evaluating a specific and limited sub-set of bus
designs using special buses outfitted for collecting study data either in a static (i.e., parked in a
stationary location) or dynamic (i.e., participants undergo simulated bus journeys over a test
track or pre-determined route) conditions followed by survey questionnaires administered to
participants at the end of the trip [e.g., 23, 24, 25, 26, 27]. This method helps overcome the
limitation of naturalistic field studies by including specific design conditions and targeted user
populations such as seniors and people with disabilities [24, 26, 28]. For example, studies by
Petzall [26] and Booz-Allen Applied Research [23] employed the use of bus journeys to study
problems regarding usability experienced by users of ambulation aids and of wheeled mobility
devices. Following the test trials, researchers interviewed participants to record their opinions of
different features on the bus, and their overall preference for the vehicle design.
Laboratory-based human factors research on transit bus usability have largely comprised
evaluations of specific components used in the bus environment such as access ramps [29] and
wheeled mobility securement systems [30, 31, 32] for comfort, safety, ease-of-use, and
efficiency. There are few usability evaluations of the vehicle environment in its entirety during
the boarding and disembarking process [24, 33, 34, 35, 36].
Full-scale simulations of buses in the laboratory create the opportunity to test multiple
concept designs that may not be available on buses in service or conditions that are difficult to
replicate in the real world. Passenger flow and behaviour can also be understood using simulated
environments in the laboratory [24, 33, 34, 35, 37]. Static environmental simulations are more
amenable for studying the dwell portions of the bus (i.e., boarding, disembarking, and interior
circulation) as compared to behavioural measures affected by vehicle dynamics such as ride
comfort and safety during abrupt acceleration and deceleration.
Study Objectives
Prior reports [3, 4, 38] suggest that low-floor bus seating layouts with inadequate clear floor
spaces and high passenger loading negatively influence the subjective experience of passengers
using wheeled mobility devices during boarding and disembarking. However, a systematic
assessment of the relative severity of the difficulty experienced, the acceptability of these
conditions, and preferences of wheeled mobility device users across multiple vehicle interior
configurations through the entire boarding and disembarking process has not received research
attention.
The objective of this study was to determine the effects of low-floor bus interior seating
configuration and passenger load on wheeled mobility device user-reported difficulty, overall
acceptability, and design preference during boarding, interior circulation, and disembarking. The
goals were to: (1) identify tasks that were most difficult for wheeled mobility device users during
boarding and disembarking, (2) examine differences in user-reported task difficulty across
wheeled mobility device users and environmental design conditions, and (3) identify wheeled
mobility device user preferences for vehicle interior layout conditions based on acceptability
ratings and a ranking of design preference.
Methodology
Study sample
Forty-eight wheeled mobility device users were recruited for this study. Inclusion criteria
required the ability to navigate a 5 degree (1:12) access ramp slope without assistance. To ensure
diversity in participant demographics and transportation modes used, participants were recruited
through multiple sources, including a local independent living centre, geriatric centre, a Veterans
Affairs Medical Center, the university community, and recruitment flyers posted at the local
public transit terminal. The study intentionally sought participants using different transport
modes to also capture the preferences and needs of those individuals who currently did not use
public transit. The university’s institutional review board approved the study procedures and all
participants provided written informed consent prior to participation. Participants received $50
USD monetary compensation for their time.
Experiment apparatus
The low-floor bus seating configurations were selected through a multi-stage process to ensure
that each of the designs was feasible and relevant. An initial understanding of the diversity of
current low-floor bus interior seating configurations was first obtained by reviewing interior
configurations of 12-m (40-ft.) length low-floor buses used by different transit agencies in the
US (e.g., LA Metro – Los Angeles, WMATA - Washington, D.C., Trimet – Portland, Port
Authority – Pittsburgh, MTA – New York City, MBTA – Boston, MARTA – Atlanta).
Representatives from industry and technical staff at a local transit agency identified five of the
most promising designs to evaluate based on technical consistency, feasibility, and compliance
with existing accessibility standards for transportation vehicles [9, 10]. Following feedback from
industry representatives three bus interior layouts were selected for inclusion in the study.
A full-scale mock-up of the front two-thirds (i.e., the entire low floor section) of a 12 m
(40 ft.) long low-floor bus was constructed in a laboratory to systematically assess user
experiences across the three bus design configurations [36]. The mock-up featured
reconfigurable seating arrangements and securement areas locations, adjustable front-wheel well
widths, different fare-payment technologies and assist features e.g., hand-holds, vertical
stanchions. Key features of the three layouts are summarized in figure 1. Commercial
electromechanical access ramps 790 mm (31 in.) wide located at the forward and rear doorway
produced a slope of 9.5 degrees (1:6) when lowered to boarding platforms that were positioned
outside the bus mock-up. This represents the maximum allowable gradient for transit vehicle
access ramps in the US. The inclined portion of the ramp at the forward doorway was 1880 mm
(74 in.) in length with 686 mm (27 in.) extending into the bus cabin. The ramp at the rear
doorway was 1194 mm (47in.) in length with the entire inclined surface located outside the bus.
The aisle width between the front wheel-well covers was 915 mm (36 in.). Two on-board fare
payment device designs were used in this study, a compact card-reader mounted on the side
panel at the rear doorway (i.e., Layouts 2 and 3) and a conventional floor-mounted fare machine
at the forward doorway in Layout 1. In all cases a proximity card was used which did not require
physical contact with the card-reader.
The number of occupied seats and unoccupied wheeled mobility securement areas was
manipulated to simulate crowding conditions found in the physical environment. Passenger load,
a measure of the utilization of the total seating capacity and calculated as the ratio of occupied
and total seats, was kept approximately constant across layouts. Clothed adult-sized inflatable
mannequins were strategically placed on-board to create high and low passenger load conditions
(figure 1). Mannequins coloured light-grey in figure 1 were present for the conditions
representing low passenger load, while both light- and dark-grey coloured mannequins were
present for conditions of high passenger load. Wheeled mobility securement areas were equipped
with fold-up seats for use by other ambulatory passengers when the securement area was not
occupied by a wheeled mobility device. Participants were required to lift up the folding seats
prior to entering the device securement area. Both securement areas were available to the
wheeled mobility device user in conditions simulating low passenger load. In conditions of high
passenger load, only one of the securement areas was available for use, with the second area
consistently occupied by a mannequin seated in a manual wheelchair (760 mm width x 1220 mm
length) secured with a four-point tie-down system.
[Insert Figure 1 near here]
Experimental procedure
Participants were first administered a questionnaire to obtain information about their age, gender,
health condition and mobility impairment, type of wheeled mobility device used, length of time
using a wheeled mobility device, and experience using public transportation. The experiment
procedure required participants to perform six independent timed boarding and disembarking
trials using the bus mock-up (i.e., 3 layouts at two levels of passenger load each). The general
sequence of boarding and disembarking tasks performed by the participant included: (1) ramp
ascent using an entry door specific to the vehicle layout, (2) fare payment with a proximity card,
(3) moving to the securement area, (4) entering and positioning in securement area, (5) exiting
the securement area, (6) moving to the exit door specific to the vehicle layout, and (7) ramp
descent.
The presentation order of the three bus layouts was counterbalanced across participants
with passenger load nested within each layout. Participants were instructed to complete the
different tasks as they normally would when using public transit, and completed one practice
trial for each bus layout. One researcher was the interviewer and provided instructions and
descriptions for the experimental trials, and administered the post-trial questionnaire. A second
researcher assumed the role of the bus driver and made announcements about when to begin
boarding and disembarking, and assisted with ramp ascent, fare payment, or lifting up the seats if
requested by the participant during the trial. Two additional team members served as spotters
near the access ramp ready to intervene in case the participant showed signs of wheelchair
instability, or potential loss of balance or fall. To reduce effects of fatigue, participants received
rest breaks of at least 10 minutes between changes in layout conditions and of at least 5 minutes
between changes in passenger load conditions. Additional rest time was provided if requested.
The experiment was conducted with one participant at a time, and required between 2.5 – 3.0
hours to complete.
Post-trial Questionnaire Instruments
Following each trial the participant completed a questionnaire that had items on: (1) task
difficulty for each of the above seven tasks using the Difficulty Rating Scale, (2) acceptability of
the overall boarding and disembarking experience combined using the Acceptability Rating
Scale, and (3) rank ordering their preference for the most recently evaluated condition in relation
to previous test conditions with the help of visual aids depicting a plan view of the layout and
passenger load. Participants were asked to provide comments supporting their ratings.
The Difficulty Rating Scale and Acceptability Rating Scale were originally developed as
measures of environmental usability [39, 40]. The Difficulty Rating Scale measures perceived
ease or difficulty of task completion using a 7- point ordinal scale ranging from -3 (very
difficult) to +3 (very easy). Respondents rate perceived task difficulty in two steps: (i) indicate if
a completed task was “difficult”, “moderate”, or “easy”; and (ii) choose a final rating from three
possible options based on the general rating provide in the first step. Likewise, the Acceptability
Rating Scale measures acceptability of a task in a two-step rating process using a 7-point ordinal
scale ranging from -3 (very unacceptable) to +3 (very acceptable). These measures have
demonstrated convergent validity with other functional measures of task performance when
using in-door environments [40] and access ramps on buses [29].
Statistical Analysis
Statistical analyses were performed using the statistical software package R v.3.1. [41].
Summary statistics were computed on the sample demographics and the nine user-reported
dependent variables, namely:
(1) Difficulty ratings obtained for the seven tasks, viz., ramp ascent, fare payment, moving to
the securement area, entry and positioning in the securement area, exiting the securement
area, moving to the exit door, and ramp descent, using an ordinal scale ranging from -3
(very difficult) to +3 (very easy).
(2) Acceptability ratings for each of the six experimental trials obtained using an ordinal
scale ranging from -3 (very unacceptable) to +3 (very acceptable).
(3) Preference rankings for the six environmental design conditions from 1 (most preferred)
to 6 (least preferred).
Three-way mixed design nonparametric analysis of variance (ANOVA) tests [42, 43]
using the R-software package ‘nparLD’ [44] were performed on each of the above nine
dependent variables. User Group (i.e., manual wheelchair, power wheelchair, and scooter users)
was the between-subjects variable and Layout (1, 2 and 3) and Passenger Load (high vs. low)
were within-subjects variables. All two- and three-way interactions were included in the three-
way ANOVA models.
All significant main and interaction effects (p < 0.05) were further evaluated using the R-
software package ‘nparcomp’, a nonparametric rank-based multiple contrast test procedure
(similar to ‘nparLD’) that computes simultaneous confidence intervals and p-values for linear
paired comparisons while controlling the family-wise Type I error rate [45]. Custom Tukey-type
contrasts for significant interaction effects were constructed to analyse paired comparisons
between levels of one factor at each level of the second factor. The study team opted to use the
‘nparLD’ and ‘nparcomp’ packages as these do not require any assumption on the underlying
distribution function and are particularly useful when analysing mixed effects in unbalanced
datasets with either ordinal or continuous dependent variables.
Observations of the users’ performance during each trial and responses to open ended
questions regarding design challenges and affordances provided insights about the self-reported
ratings of sub-task difficulty, overall acceptability and design preference.
Results
Sample Demographics
The study sample consisted of 18 manual wheelchair (MWC) users, 21 powered wheelchair
(PWC) users and 9 scooter users, with roughly equal number of men (54%) and women (46%).
The mean age was 50.2 (SD = 10.5, range = 25 – 68) years, the mean duration using a wheeled
mobility device was 7.4 (SD = 7.9, range = 0.08 – 38) years. MWC users on average were
younger (mean = 46.7, SD = 7.9, range = 27 – 58 years) compared to PWC users (mean = 50.4,
SD = 10.8, range = 25 – 62 years) and scooter users (mean = 56.8, SD = 12.1, range = 31 – 68
years) however these differences in age were not significant (F (2, 45) = 3.032, p = 0.058). User
groups differed in their experience of using a wheeled mobility device (F (2, 45) = 4.868, p =
0.012). MWC users reported use of a mobility device for significantly greater period of time
(mean = 11.4, SD = 10.1, range = 1 – 38 years) compared to PWC users (mean = 5.1, SD = 4.8,
range = 0.08 – 20 years; t (0.05, 45) = 2.73, p = 0.018) and scooter users (mean = 4.6, SD = 5.3,
range = 0.17 – 16 years; t (0.05, 45) = 2.53, p = 0.030). Ten participants (21%) were left-hand
dominant.
Participants reported a broad range of medical conditions, with cerebral palsy (29%),
multiple sclerosis (10%) and paraplegia (10%) being the most frequently reported. Three
participants categorized as ‘Other’ included individuals with COPD, a foot ulcer, and a liver
transplant. Ambulation capabilities among the participants was low with 21 participants (44%)
indicated being unable to walk or use stairs, and an additional 17 (35%) reported having a lot of
difficulty walking or using stairs. Forty-four participants (92%) indicated having little to no
difficulty with upper extremity function such as using handrails or grab-bars.
Approximately half the sample had some prior experience using fixed route bus services
(Table 1). Participants reported using a range of different transport modes including fixed route
bus (48%) and metro rail (56%) services with varying frequency suggesting some familiarity
with the local public transit system. Half the sample (50%) occasionally used demand response
services like paratransit, while others never use public transit or rarely travel outdoors more than
once a month.
[Insert Table 1 near here]
Ratings and Preferences
Figures 2, 3 and 4 provide the median values for the seven sub-task difficulty ratings by Layout
and Passenger Load for users of MWCs, PWCs, and scooters, respectively. The data indicates a
greater difficulty in ramp ascent for MWC users, and generally an increased difficulty for all user
groups in tasks related to interior circulation (i.e., moving to the securement area, entering and
positioning in securement area, exiting the securement area, and moving to the exit door),
particularly in conditions of high Passenger Load.
[Insert Figures 2, 3 and 4 near here]
Median overall acceptability ratings and median preference rankings stratified by User
Group, Layout and Passenger Load are shown in figures 5 and 6, respectively. Layout 1:
Forward Entry – Exit was and Layout 3: Rear Entry – Exit was generally acceptable to users of
MWCs and PWCs in conditions of low and high Passenger Load, but moderately unacceptable
and neutral for scooter users in conditions of high Passenger Load. The median acceptability
rating in Layout 2: Rear Entry – Forward Exit for MWC users was negative. Median preference
rankings were generally higher in Layout 3 across User Group (figure 6). Median rankings were
also more diverse in conditions of High vs. Low Passenger Load.
[Insert Figures 5 and 6 here]
Table 2 presents summary results from the three-way nonparametric ANOVA tests
performed on the seven sub-task difficulty ratings, overall acceptability rating and preference
ranking to examine differences across User Group, Layout and Passenger Load. None of the
three-way interaction effects were statistically significant. Following is a description of the
ANOVA results for each dependent measure along with key themes identified in the
participants’ comments provided during the rating procedure.
[Insert Table 2 near here]
Ramp Ascent
Difficulty ratings for ramp ascent were significantly different across User Group (p < 0.001),
with MWC users reporting greater difficulty (i.e., lower rating) than users of PWCs and scooters.
Difficulty ratings also differed statistically by Layout (p = 0.004). Boarding at the forward
doorway (Layout 1) was rated more difficult compared to layouts with rear boarding, i.e.,
Layouts 2 and 3. Not surprisingly, Passenger Load had no impact on difficulty in ramp ascent.
MWC users were observed relying on the handrails for ramp ascent, requesting driver
assistance with wheelchair propulsion (n = 3, 16.7%) or boarding the ramp facing rearwards (n =
3, 16.7%) as compensatory strategies. A few PWC users expressed concerns about inadequate
ramp width (n = 3; 14.3%), however the majority of PWC users and scooter users had no
difficulty with ramp ascent.
Fare Payment
Difficulty ratings for the fare payment task differed significantly by Layout (p = 0.005), with fare
payment using the side-mounted card reader at the rear doorway (i.e., Layouts 2 and 3) rated
significantly easier compared to the floor-mounted fare machine used at the forward doorway,
i.e., Layout 1. No significant differences across User Group and Passenger Load were found.
Problems with the floor-mounted fare machine at the front doorway in Layout 1 included
inconvenient and inadequate manoeuvring space for all user groups. Users of PWCs and scooters
had difficulty approaching and reaching to the fare-card reader, while some were unable to
obtain a direct line of sight to the display screen. The absence of a levelled floor near the fare-
box at the front doorway (Layout 1) also caused problems for MWC users requiring them to
either “lock the wheelchair” or “hold on to wheel with one hand to prevent it from rolling back”.
A levelled and unobstructed floor space combined with a side approach were stated as primary
reasons for preferring the fare-payment condition at the rear doorway in Layouts 2 and 3.
Moving to the Securement Area
Difficulty ratings for moving to the device securement area were statistically similar across User
Group but differed significantly across Layout (p = 0.012). Participants reported significantly
greater difficulty in Forward Entry – Exit (Layout 1) compared to Rear Entry – Exit (Layout 3)
condition. Significantly greater difficulty was observed in conditions of high vs. low Passenger
Load (p < 0.001).
Post-hoc analysis of the significant interaction effect between Layout and Passenger Load
showed significantly greater task difficulty ratings in high vs. low Passenger Load in the Rear
Entry – Forward Exit condition (i.e., Layout 2; with longitudinal seating throughout) but not for
Layouts 1 and 3. Further, significantly greater difficulty was noted in Forward Entry – Exit
(Layout 1) over Layout 2 in conditions of low Passenger Load, and in the Rear Entry – Forward
Exit condition (i.e., Layout 2) over Rear Entry – Exit (Layout 3) conditions of high Passenger
Load.
Entry and Positioning in the Securement Area
The task of entering and positioning in the securement area was rated significantly more difficult
(i.e., lower) in conditions of high compared to low Passenger Load (p < 0.001), independent of
User Group or Layout. Scooter users reported marginally greater difficulty in completing this
task compared to users of MWCs and PWCs but this difference was not statistically significant.
Unlike the Forward Entry – Exit (Layout 1) condition, entry and positioning in the
securement area in conditions with Rear Entry (i.e., Layouts 2 and 3) did not require users to
perform a 180-degree turn. However, this advantage was less prominent in conditions of high
Passenger Load. Participants found the space to be quite inadequate resulting in accidental
collisions or requests for operator assistance to create more space by repositioning the other
wheelchair. In conditions of low Passenger Load in the Forward Entry – Exit (Layout 1)
condition, a few users also “lifted (folded up) seats on both sides (of the bus) to make space”
anticipating problems in a 180-degree turn.
Twelve of the 48 (25%) of manual and power wheelchair users reported difficulties with
lifting the fold-up seats in the securement area due to insufficient upper extremity strength and
the inability to get close enough to the seat lever. In these cases, help from the bus operator was
sought for lifting the seats after an initial attempt or immediately upon fare payment. Difficulty
locating the lever for unlocking and folding the seats was also a problem. In the Rear Entry –
Forward Exit condition (i.e., Layout 2) two participants moved past the lever and hence had to
rotate and reach posteriorly to operate the lever.
Exiting the Securement Area
Analysis of the difficulty ratings for exiting the securement area showed significant differences
across Layout (p = 0.025) and Passenger Load (p < 0.001). Post-hoc analysis of the interaction
between Layout and Passenger Load showed greater difficulty in high vs. low Passenger Load
for Layout 3 (i.e., rear disembarking). Significant differences were also observed in high
Passenger Load conditions, with greater task difficulty in Layout 3 (i.e., rear door egress
requiring a 180-degree to exit the securement space) compared to Layouts 1 and 2 (i.e., exiting at
the front doorway).
Moving to the Exit Door
The reported difficulty for moving to the exit door was significantly greater (i.e., lower rating) in
conditions of high vs. low Passenger Load (p = 0.002). Analysis of the interaction effect between
Layout and Passenger Load did not show statistically significant differences in pairwise
comparisons.
Ramp Descent
Difficulty in ramp descent differed significantly across User Group (p = 0.010), with MWC users
reported greater difficulty (i.e., lower rating) compared to users of PWCs and scooters. Ramp
descent in Layout 1 was rated slightly more difficult but not significantly different compared to
Layouts 2 and 3 (i.e., conditions with the fare payment device at the rear-doorway), the presence
of the floor mounted fare payment device being one key difference in design. Nine participants
commented that approaching and aligning onto the ramp for descent was more problematic at the
front doorway with a “sharp turn right by the driver seat”. These users opted to “grab the
handrails to control the descent” or requested verbal cues from the operator “to help keep straight
on the ramp.”
Overall Acceptability Rating
There was a significant interaction between User Group and Passenger Load (p = 0.048). Users
of MWCs and PWCs rated test conditions with low Passenger Load significantly more
acceptable compared to high Passenger Load. Acceptability ratings by scooter users were general
lower compared to users of MWCs and PWCs but did not show significantly differences across
Passenger Load.
Ranking of Design Preference
Preference rankings for the six test conditions differed significantly by Layout (p = 0.007) and
not by User Group. Rear Entry – Exit (Layout 3) was ranked significantly higher compared to
Forward Entry – Exit (Layout 1) and Rear Entry – Forward Exit (Layout 2) independent of User
Group and Passenger Load. Overall, conditions with low Passenger Load were rated significantly
better than high Passenger Load independent of User Group or Layout (p < 0.001). The
exception was among scooter users where Rear Entry – Exit (Layout 3) in high Passenger Load
was preferred over Forward Entry – Exit (Layout 1) in low Passenger Load. A post-hoc analysis
of the significant interaction between User Group and Layout indicated a significantly higher
preference for Rear Entry – Exit (Layout 3) compared to Rear Entry – Forward Exit (Layout 2)
among MWC users.
Discussion
Boarding and Disembarking Task Difficulty
Although they were all compliant with federal design standards for accessibility [9, 10], the three
vehicle configurations evaluated in our study posed different usability challenges to wheeled
mobility device users.
Ramp Usage during Boarding and Disembarking
Analysis of user-reported difficulty ratings revealed the most difficult tasks for MWC users
include ramp ascent followed by ramp descent to a lesser extent. The access ramps at the front
and rear-doorway in this study were at a slope of 9.5 degrees (1:6). This slope was less than the
maximum gradient of 14.0 degrees (1:4) currently permissible for access ramps by federal
standards for transit vehicle accessibility [10] yet posed problems for manual wheelchair users.
Recent laboratory studies on ramp usability [29] and naturalistic field studies on boarding and
disembarking [8] support our findings on problems faced by wheeled mobility device users when
using access ramps. Lower ramp slopes may reduce difficulty in using the ramp, fare payment
and traveling to the securement area, especially when boarding at the forward doorway (Layout
1). Lenker, Damle [29] recommend a slope of 1:8 for access ramps as best practice though
achieving this would require improving the design of ramps and/or conditions at bus stop pads
(e.g., raised concrete platforms).
Interestingly, three manual wheelchair users and one scooter user in our study opted to
ascend the access ramp facing rearwards since they had some lower extremity function but
insufficient upper extremity strength or impairment (e.g., shoulder pain) to propel up the ramp.
This strategy of ascending the access ramp facing rear-wards led to subsequent problems and
unsafe conditions in the bus interior when positioning for fare payment, and manoeuvring to the
securement area while avoiding accidental contact with passengers. A retrospective analysis of
ramp ascent from bus surveillance footage by Frost, Bertocci [6] noted significantly greater
number of adverse incidents (such as impacting the ramp edge barrier or vehicle door, requiring
multiple forward/reverse manoeuvres) for wheeled mobility device users that ascended the ramp
in a rear-facing vs. a forward-facing orientation. In their study, wheeled mobility device users in
27.2% (68 of 250) of the boarding observations ascended the ramp rear-facing and were mostly
PWC users (48.5%) followed by MWC users (39.7%) and scooter users (11.8%).
Fare Payment
Fare payment was a comparatively easier task than ramp ascent and descent (for MWC users)
and interior circulation. However, difficulties with fare payment were encountered with fare
payment at the front doorway using the conventional floor-mounted fare payment device which
requires users to perform an extended reach. Based on measurements made on buses in
operation, the top of the standard floor-mounted fare machine in the mock-up was 1195 mm (47
in.) high and with the card reader at 1140 mm (45 in.) from the floor. Although compliant with
accessibility guidelines, these dimensions coupled with the lack of knee and toe clearance space
which limits a forward approach and considerable trunk involvement in a forward lean places the
card reader outside the comfortable reach zone. Design improvements are needed that involve
lowering or relocating the fare-box to improve reach and line of sight. Users expressed general
satisfaction with the proximity card as it did not require handling coins, producing exact change
or performing a precise reaching motion such as when inserting coins or swiping a magnetic strip
card.
Interior Circulation
Interior circulation was found to be problematic particularly in conditions of high Passenger
Load and for users of scooters and PWCs when a 180 deg. turn was required. Moving to the
securement area in the Forward Entry – Exit (Layout 1) condition required wheeled mobility
device users to move past the wheel-wells over the front axle to reach the securement space. For
all three layouts, the presence of the other wheelchair on-board in conditions of high Passenger
Load greatly impeded circulation, with users across all three groups reporting accidental
collisions with the wheelchair, wheelchair tie-downs, and needing driver assistance to create
more space by displacing fellow passengers. Instances and concerns of accidental collisions were
more severe in conditions of high Passenger Load in Layout 2 (i.e., longitudinal seating),
wherein the user had to manoeuvre around the wheelchair and run the risk of “running over
people’s feet” on the road-side or “bumping into the other wheelchair and tie-down” on the curb-
side, in stark contrast to low Passenger Load when the aisle is completely unobstructed. When
exiting the securement area, users of power chairs and scooters reported experiencing “a tight
space” and “getting stuck coming out of the aisle” across all three layouts, particularly in
conditions of high Passenger Load when impeded by the second wheelchair and the wheelchair
tie-down system. When moving to the exit door, comments by users reflected in adequate
manoeuvring space near the wheel-wells in Layouts 1 and 2 that required disembarking at the
front doorway, collisions with the wheelchair tie-downs and with the base of the floor-mounted
fare-box in the Forward Entry – Exit (Layout 1) condition. Collisions with the wheelchair tie-
down and the second wheelchair were also reported under high Passenger Load in the Rear-Exit
condition (Layout 3).
Our findings indicate that scooter users report greater difficulty with interior circulation
compared to MWC and PWC users regardless of the vehicle layout. Prevailing conditions on
low-floor buses could deter scooter users from using public transit altogether. This could explain
the smaller samples of scooter users observed in naturalistic field observation studies on public
transit [8, 46] and consequently an under-reporting of related transportation issues in research
literature.
Self-reported Difficulty, User Preference and other Measures of User Performance
Analysis of preference rankings and acceptability ratings suggest that users favoured an interior
layout configuration with boarding and disembarking at the rear doorway, i.e., Layout 3 in this
study. This condition allowed for a more straightforward entry into the securement area but a
difficult 180-degree turn during disembarking. One explanation from participants preferring this
layout was that it afforded time on-board to anticipate and plan the 180-degree turn prior to
disembarking. Interior configurations requiring complex manoeuvres during the boarding phase,
which are not necessarily anticipated prior to boarding (e.g., Layout 1) or posed undue risk to
fellow passengers causing anxiety (e.g., Layout 2), were rated less favourably. Boarding and
disembarking times and frequency of critical incidents, while only moderately correlated with
difficulty ratings were on average lower in Layout 3 supporting the findings of this study [36,
47].
Stress and Anxiety
Participants in this study reported being stressed as they would when using public transit due to
space constraints, time pressure (reinforced by instructions from the experimenter to be mindful
of time as they normally would in real life), and being alert of the personal space of co-
passengers represented by mannequins. Participants also made unprompted comments that the
presence of real people (as opposed to mannequins) would have further influenced their ability to
perform the necessary manoeuvres. Some felt they would become self-conscious while others
expressed concerns over potential for injury to other passengers. Yet others were concerned that
passengers might not be willing to move and allow them space to turn. Such stress or anxiety
associated when traveling in crowds may cause users to avoid public transit entirely.
A natural tendency to avoid delays and minimize inconvenience to others can also induce
unsafe behaviour such as opting not to secure the wheelchair, avoiding assistance with using the
access ramps, or hurrying through with ramp ascent and descent and thereby comprising
individual safety. Previous studies suggest high prevalence of misuse or non-use of the
wheelchair tie-down system in the field [7, 48, 49, 50, 51] placing wheeled mobility device users
at an increased risk of injury during travel [52]. While the usability of these systems has been
studied extensively, other inefficiencies in the boarding process such as ramp ascent and interior
circulation could result in avoiding tasks related to wheelchair and occupant securement, which
may be perceived as unnecessary or optional in an attempt to minimize further delay.
Implications for Rehabilitation
Understanding transit usability barriers, perceptions and preferences of wheeled mobility users is
an important consideration for clinicians prescribing mobility-related device interventions. We
highlight two specific considerations, namely, wheeled mobility device selection and skills
training.
Wheeled mobility device selection
PWCs in our study were pre-dominantly mid-wheel-drive (n = 16, 73%) which are more
manoeuvrable in confined spaces [14]. Research on the shapes and sizes of wheeled mobility
devices currently in use indicate that there is great diversity in device types (including within
categories of manual wheelchairs, powered wheelchairs, and electric scooters) [11, 12] and a
trend towards larger occupied device dimensions than decades previous [2, 4, 13, 53]. This
complicates wheelchair accommodation on low-floor buses. The Americans with Disabilities Act
Accessibility Guidelines for transportation vehicles currently requires a minimum of two
wheeled mobility securement areas each with a minimum size of 760 mm x 1220 mm (30 in. x
48 in.) to be provided in vehicles greater than 12 m (22 ft) in length [9]. Very few securement
areas in reality exceed these dimensions. However, static measurements of occupied width and
length on 369 wheeled mobility devices in the U.S. found that approximately 30% of occupied
manual wheelchairs and 50% of occupied power wheelchairs and scooters exceed these
minimum dimensions [13]. The consensus view among transit operators is that the full range of
scooters are unlikely to be compatible with the full range of buses and that any policy of full
access would be difficult to operate in practice [38]. These problems are not unique to the US.
Research studies from the UK suggest similar concerns regarding increased wheeled mobility
sizes and challenges to accommodation on public transit vehicles [54]. Given prevailing
standards provisions, rehabilitation engineers and therapists need to consider the transportation
needs of clients and the occupied device size relative to the space available for wheelchair
circulation and securement areas on contemporary low-floor buses.
Wheeled mobility skills and transit training
Findings from this study support the notion that the design and manoeuvring characteristics of
wheeled mobility devices combined with the operating skill of the user influences efficient
interior circulation on transit vehicles [53]. Furthermore, our findings provide insights into
manoeuvring skills necessary for successful boarding and disembarking, and translate into
training goals and interventions to improve the functional capacity of wheeled mobility device
users to meet the demands of using public transit vehicles in a safe and efficient manner. For
instance, clinicians need to make sure MWC users can push their chair up and down a narrow
ramp. Users of PWCs and scooters need to demonstrate the ability to manoeuvre tight spaces,
and with other people in close proximity. Wheeled mobility device users also need to have the
seated reach necessary for fare payment on transit buses in their region. Future studies should
aim to quantify the effects of such training interventions on outcomes such as transit use,
consumer satisfaction, quality of life and social participation. Lastly, clinicians can recommend
clients to services that provide travel training on how to use local public transit in a safe and
efficient manner.
Self-reported measures of performance along with objective measures such as the
duration and level of assistance required for boarding and disembarking using full-scale mock-
ups may provide an alternate model for determining readiness for using fixed-route buses or
eligibility for paratransit. In an effort to reduce strain on the paratransit service, many transit
agencies have constructed indoor bus mock-ups which are used both for travel training and
assessing paratransit eligibility. Training increases confidence in the rider’s ability to navigate
the fixed-route system and improves coping skills. Some agencies use actual vehicles to do
training and eligibility evaluations at housing locations, social and recreation centres.
Study Limitations
Data collection occurred in an idealized laboratory environment using a static mock-up of a low-
floor bus. Thus the results do not reflect the potential influence of outdoor environmental factors
such as temperature, rain, snow, and noise, vehicle dynamics (e.g., anxiety about the bus starting
to move before the passenger is seated) and psychosocial considerations (e.g., presence of co-
passengers). Nonetheless, this research provides a baseline of best-case performance that can be
a useful basis for comparisons with future field studies in real-world environments. Controlled
laboratory studies such as this provide the opportunity to make detailed functional assessments
and performance measurements, but they do limit inferences on the relationship between
environmental conditions, user characteristics and task performance to the conditions studied.
For example, the advent of automated vehicles will present new problems and opportunities due
to the lack of drivers. On the one hand, the design of automated vehicles will necessitate a higher
standard of usability to insure independent use without driver assistance. On the other hand, such
vehicles will have more space due to the removal of driver stations and fare machines.
Seating configurations and securement areas on low-floor buses can differ by vehicle
manufacturer and requirements specified by transit agencies during vehicle procurement. Only
three layouts were compared in this study. Over time, the simulation environment can be used to
test and develop accessibility benchmarks for a broader range of bus layouts, wheelchair
securement technologies, wheeled mobility device types, with updates as new technologies and
models evolve. For example, studies in Europe have shown that rear-facing securement areas are
safe and time-efficient in urban buses, but some users dislike being the only ones traveling on the
bus facing rearwards [19].
The study presently focused only on barriers and facilitators to usability relating to the
physical bus environment. Quantitative measurements of the relative importance of barriers in
the physical and psychosocial environment spanning the entire travel chain are needed [55].
Wheeled mobility device users were evaluated in this study to address a demonstrated need for
improved usability [4, 5, 7] in light of proposed and subsequently finalized changes to U.S.
accessibility guidelines that could impact wheeled mobility device users on transit buses [56]. As
part of an inclusive design process addressing the design needs of other user groups, including
older adults, users of ambulation aids, and persons with sensory and cognitive impairments are
also necessary [57, 58].
Conclusions
This study identified tasks that were most difficult for wheeled mobility device users during
transit vehicle boarding and disembarking along with acceptability ratings and a ranking of
design preferences for six vehicle interior layout conditions. Ramp ascent was deemed the most
difficult task for manual wheelchair users, whereas tasks related to interior circulation were rated
most difficult by users of power wheelchairs and scooters. Overall, the ability to independently
ascend and descend on access ramps, manoeuvre in tight spaces, and perform seated reaches for
fare payment were critical to successful boarding and disembarking and represent tasks that can
be targets of intervention by clinicians.
Understanding the transit usability barriers, perceptions and preferences of wheeled
mobility device users can help in developing, prioritizing, and implementing of evidence-based
rehabilitation interventions. The study also demonstrates the utility of environmental simulations
for engaging users with disabilities to identify transit usability problems in a safe and systematic
manner. Such studies are extremely important to conduct prior to production of new vehicles,
especially if the new vehicles take radical departures from existing models.
Acknowledgements
The contents of this manuscript were developed under grants from the National Institute on Disability,
Independent Living, and Rehabilitation Research (NIDILRR) through the RERC on Accessible Public
Transportation (RERC-APT; grant numbers #H133E130004 and #H133E080019) and a field-initiated
project grant (grant number #90IF0094-01-00). NIDILRR is a Center within the Administration for
Community Living (ACL), Department of Health and Human Services (HHS). The contents of this
manuscript do not necessarily represent the policy of NIDILRR, ACL, HHS, and you should not assume
endorsement by the Federal Government.
Declaration of Interest
The authors report no potential conflicts of interest.
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List of Tables and Figures
Table 1. Self-reported frequency of use of different transportation modes stratified by user group
(n = 48). MWC: Manual Wheelchair Users; PWC: Power Wheelchair Users.
Table 2. Summary results for the significant main and interaction effects (p < 0.05) and pair-wise
Tukey comparisons of interest (p < 0.05) from the non-parametric three-way mixed effects
analysis of variance for user-reported task difficulty, overall acceptability rating, and preference
rank. None of the three-way interactions were significant and hence not shown. MWC: Manual
Wheelchair Users; PWC: Power Wheelchair Users; L1: Layout 1: Forward Entry – Exit; L2:
Layout 2: Rear Entry – Forward Exit; L3: Layout 3: Rear Entry – Exit.
Figure 1. Plan views and key features of the three bus layout configurations selected for study.
Mannequin placement for simulated conditions of low (light grey) and high (both light and dark
grey) Passenger Load are also depicted. Table modified from [36].
Figure 2. Median task difficulty ratings (-3 = very difficult, 3 = very easy) Layout and Passenger
Load conditions for manual wheelchair users (n = 18).
Figure 3. Median task difficulty ratings (-3 = very difficult, 3 = very easy) by Layout and
Passenger Load conditions for power wheelchair users (n = 21).
Figure 4. Median task difficulty ratings (-3 = very difficult, 3 = very easy) by Layout and
Passenger Load conditions for scooter users (n = 9).
Figure 5. Median values for overall acceptability rating (-3 = very unacceptable, 3 = very
acceptable) stratified by layout, passenger load, and user group (manual, power and scooter
device users).
Figure 6. Median values for preference rank (1st = most preferred, 6th = least preferred)
stratified by layout, passenger load, and user group (manual, power and scooter device users).
Table 1. Self-reported frequency of use of different transportation modes stratified by user group
(n = 48). MWC: Manual Wheelchair Users; PWC: Power Wheelchair Users.
Transport modes used
User Group
MWC (n = 18)
PWC (n = 21)
Scooter (n = 9)
Total (n = 48)
Fixed Route Bus
>= once per week or more
17% (3)
24% (5)
22% (2)
21% (10)
>= once per month
28% (5)
33% (7)
11% (1)
27% (13)
Never
56% (10)
43% (9)
67% (6)
52% (25)
Light rail, metro
>= once per week or more
22% (4)
19% (4)
33% (3)
23% (11)
>= once per month
33% (6)
38% (6)
22% (2)
33% (16)
Never
44% (8)
43% (9)
44% (4)
44% (21)
ADA Paratransit
>= once per week or more
22% (4)
19% (4)
22% (2)
21% (10)
>= once per month
17% (3)
48% (10)
11% (1)
29% (14)
Never
61% (11)
33% (7)
67% (6)
50% (24)
Private automobile
>= once per week or more
72% (13)
38% (8)
56% (5)
54% (26)
>= once per month
22% (4)
29% (6)
33% (3)
27% (13)
Never
6% (1)
33% (7)
11% (1)
19% (9)
Table 2. Summary results for the significant main and interaction effects (p < 0.05) and pair-wise Tukey comparisons of interest (p < 0.05) from
the non-parametric three-way mixed effects analysis of variance for user-reported task difficulty, overall acceptability rating, and preference
rank. None of the three-way interactions were significant and hence not shown. MWC: Manual Wheelchair Users; PWC: Power Wheelchair
Users; L1: Layout 1: Forward Entry – Exit; L2: Layout 2: Rear Entry – Forward Exit; L3: Layout 3: Rear Entry – Exit.
Dependent Variable
User Group
Layout
Passenger Load
User Group x
Layout
Layout x
Passenger Load
User Group x
Passenger Load
User-reported Difficulty
(-3 = very difficult ; +3 = very easy)
1. Ramp Ascent
F = 19.227, p < 0.001
(PWC, Scooter) > MWC
F = 6.639, p = 0.004
L3 > L1
-
-
-
-
2. Fare Payment
-
F = 6.119, p = 0.005
(L2, L3) > L1
-
-
-
-
3. Moving to
Securement Area
-
F = 4.705, p = 0.012
L3 > L1
F = 35.573, p <
0.001
Low > High
-
F = 14.729, p <
0.001
L2: Low > High
Low: L2 > L1
High: L3 > L2
4. Entry & Positioning
in the Securement
Area
-
-
F = 15.707, p <
0.001
Low > High
-
-
-
5. Exiting the
Securement Area
-
F = 3.814, p = 0.025
F = 11.19, p < 0.001
Low > High
-
F = 14.162, p <
0.001
L3: Low > High
High: L1 > L3
High: L2 > L3
-
6. Moving to Exit Door
-
-
F = 10.004, p =
0.002
Low > High
-
F = 5.127, p = 0.007
-
7. Ramp Descent
F = 5.281, p = 0.01
PWC > MWC
Scooter > MWC
-
-
-
-
Overall Acceptability
(-3 = very unacceptable;
+3 = very acceptable)
-
-
F = 46.16, p < 0.001
Low > High
-
-
F = 3.043, p =
0.048
MWC: Low > High
PWC: Low > High
Preference Ranking
(1 = most preferred;
6 = least preferred)
-
F = 5.348, p = 0.007
L3 < L1
L3 < L2
F = 96.741, p <
0.001
Low < High
F = 2.739, p = 0.04
MWC: L3 < L2
-
-
