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International Cycling Safety Conference 2015
15-16 September 2015, Hannover, Germany
ABSTRACT
The ease of movement while driving an Electric Bicycle (EB) inspires many. The total number of
EBs in Germany has now grown to 2.1 million. In the medium term EBs are estimated to have a
market share of 15 % in the overall bicycle market. In addition to assist the driver while
accelerating the bicycle, the available electrical energy on EBs also offers the possibility to
support the driver during deceleration. This is the initial point for the interdisciplinary research
project BikeSafe aiming to develop an innovative Braking Dynamics Assistance system (BDA)
for bicycles with hydraulic brakes. The essential function of the BDA is to prevent both major
critical braking situations for single-track vehicles: front wheel lockup and nose-over (falling
over the handlebars).
In order to ensure a target group oriented and accident specific development of the BDA, a
better understanding of EBs’ accident situations being influenceable by active safety systems is
necessary. A substantial problem is the well-known underreporting of bicycle accidents in
official statistics based on police reports. Especially when investigating single-vehicle accidents
in which both critical braking situations mainly occur this phenomenon needs to be addressed
by an adequate approach.
For this reason, the present paper evaluates a literature review of studies on underreporting,
single-vehicle accidents, cyclist behaviour, and changed mobility patterns due to EBs. Based on
these findings several research questions concerning the development of the BDA, which were
additionally considered within an empirical survey (1,040 participants, representative for
German adults above 18), are described and discussed. For example, a proportion of single-
vehicle accidents on all accidents of 65 % was determined. In conclusion, the results of this
paper provide both quantitative and qualitative information to estimate the potentials of and
to define future requirements for the BDA.
Keywords: sustainable mobility, electric bicycles, accident research, single-vehicle crashes.
Empirical Survey on Bicycle Accidents to estimate
the Potential Benefits of Braking Dynamics Assistance Systems
Oliver Maier1, Martin Pfeiffer2, Christa Wehner3, Jürgen Wrede4
1
Institute of Applied Research
Pforzheim University
Tiefenbronner Str. 65, 75175 Pforzheim, Germany
e-mail: oliver.maier@hs-pforzheim.de
2
Department of Information Technology
Pforzheim University
Tiefenbronner Str. 66, 75175 Pforzheim, Germany
e-mail: martin.pfeiffer@hs-pforzheim.de
3 Department of Market Research
Pforzheim University
Tiefenbronner Str. 65, 75175 Pforzheim, Germany
e-mail: christa.wehner@hs-pforzheim.de
4 Department of Mechanical Engineering
Pforzheim University
Tiefenbronner Str. 66, 75175 Pforzheim, Germany
e-mail: juergen.wrede@hs-pforzheim.de
2
1 INTRODUCTION
1.1 Vulnerable Road Users
In its policy orientations on road safety, the European Commission is putting particular
emphasis on the need to improve the safety of Vulnerable Road Users (VRUs) [1]. VRUs are
defined as those participants in traffic that are not protected by any mechanical system:
pedestrians, bicyclists and motorcyclists [2].
Actually, VRUs account for about 45 % of European Union (EU) road fatalities [1]. Although the
total number of fatalities and severe injuries due to traffic accidents is decreasing, the number
of VRUs that are killed and wounded in traffic tends to decrease at a much slower pace [1-2,
4]. While pedestrians form the largest sub-group of all fatalities, Powered Two-Wheelers
(PTWs) are involved in a disproportionately high percentage of serious and fatal accidents [1].
Due to the high speed reachable and the weight of the vehicle, single-vehicle accidents
involving PTWs can also be fatal or lead to very severe injuries [2].
Even today, cyclists are the passenger group that comprises those individuals who are the
most seriously injured, nearly 2,000 of approximate 4,500 in Sweden in 2012 [3]. In the whole
EU cyclists account in official accident statistics for ca. 7 % of all road fatalities [5], and there
are concerns that the growing number of Electric Bicycles (EBs) – as a new subgroup of PTWs –
might cause additional safety risks [1].
Especially the ease of movement while driving an EB inspires many. The total number of EBs in
Germany has grown to 2.1 million [6]. In the medium term EBs are estimated to have a market
share of 15 % in the overall bicycle market [7]. Summarizing, the provision of power assistance
to the rider potentially will extend the role of bicycles in urban transport [8]. From a societal
point of view this modal shift from mainly cars to bicycles is a very desirable development. A
study in the Netherlands proves that, on average, for individuals shifting their mode of
transport the estimated health benefits of cycling are substantially larger than the risks
compared to car driving [9].
Considering the specific safety risks of all VRUs, there is an important need for the
development and introduction of advanced technologies and systems for VRU protection. First
priority should be on collision avoidance or mitigation [1].
1.2 Braking Dynamics Assistance System
In-vehicle systems (active safety systems), roadside systems (e.g. camera’s overlooking a
crossing and identifying road users with their future paths), car-to-infrastructure and
infrastructure-to-car communication, and an intelligent traffic management system are the
most promising technical ways for improving the safety of VRUs [2]. Regarding active safety
systems, the available electrical energy on EBs offers the possibility to support the cyclist
during deceleration. For this reason, Grimaldi considers an Anti-lock Braking System (ABS) on
EBs as a realistic and effective measure for improved safety [3].
The interdisciplinary research project BikeSafe links precisely to this idea. It aims at the
development of an active Braking Dynamics Assistance system (BDA) for bicycles equipped
with hydraulic brakes. The BDA to be designed will target to prevent both major critical braking
situations for single-track vehicles: front wheel lockup and nose-over (falling over the
handlebars). In order to ensure a target group oriented and accident specific development of
3
the BDA, a better understanding of EBs’ accident situations - being influenceable by active
safety systems - is necessary. A substantial problem is the well-known underreporting of
bicycle accidents in official statistics based on police reports.
1.3 Research Questions
The aims of this paper are to provide both quantitative and qualitative information for
estimating the potential benefit of such a BDA and to define future requirements for it. In
detail, the following issues are examined:
• Validity and limitations of official accident statistics based on police, hospital and
expert (e.g. German In-Depth Accident Study, GIDAS) reports
• Underreporting of bicycle accidents and resulting impacts on the proportion of single-
vehicle accidents
• Effects on the current accident situation caused by changes in mobility patterns due to
electrical bicycles
• Cyclist behaviour and accident cause factors with special focus on the critical braking
situations to be prevented by the BDA
The paper begins with a literature review of studies on underreporting of bicycle accidents in
official statistics. Next studies on single-vehicle accidents and cyclist behaviour investigated by
both health care data analysis with additional surveys and Naturalistic Cycling Studies (NCS)
are analysed. Subsequent sections examine changes in mobility patterns due to EBs and
explains the methodology of the conducted survey representative for German population
above 18. We then present the results of the study to provide both quantitative and
qualitative information to estimate the potentials of the BDA. Based on these findings several
research questions concerning the development of the BDA are described and discussed. The
final section concludes with the most important findings and their implications for future
works.
2 MATERIAL AND METHODS
2.1 Underreporting of Bicycle Accidents in Official Statistics
Comparing bicycle use among different countries reveals enormous differences from near
absence to widespread use. While there are countries where cycling is mostly practiced for
recreation, cycling is a substantial part of everyday life in other countries such as the
Netherlands. Although cycling activities also take place in rural areas, the majority of the
bicycle kilometres in the latter countries are travelled in towns and cities. In conclusion,
country-specific differences in bicycle use lead to significant differences in bicycle culture,
cyclists’ role in traffic, and technical and regulatory measures employed for safer cycling [4].
Despite the difficult comparability of individual countries, it can be noted that all worldwide
accidents statistics indicate that cyclists have a relatively high crash rate compared to other
road users [1-2]. When drawing conclusions from official statistics, three substantial issues are
challenging: underreporting of bicycle accidents, age distribution of injured cyclists, and basic
problems cause by bicycle design [4].
4
Especially when non-fatal bicycle injuries are concerned, statistics suffer from underreporting
[10]. Some countries have made initial attempts to link data sources, such as police and
hospital data, in order to overcome at least part of this problem [4]. A study in the Netherlands
[11] compared data for serious traffic injuries stemming from hospital data bases with police
data. It was concluded that the police records contained only 59 % of the seriously injured
cyclists that crashed with motor vehicles and only about 4 % of those being injured with no
motor vehicle involved. Similar findings were obtained in studies carried out in the German
bicycle-capital Muenster [12-13] and in the French County Rhône-Alpes [14].
In summary, confirmed by the results of a meta-analysis of studies made in 13 countries [15],
reporting rate tends to be highest for collisions between cyclists and cars and lowest for
cyclists on single-vehicle accidents (the latter less than 10 % in all countries studied).
2.2 Single-Vehicle Accidents and Cyclist Behaviour
Both critical braking situations (front wheel lockup and nose-over) mainly happen in single-
vehicle accidents. For this reason, as the studies investigating underreporting show, an
accident-specific development of the BDA based on official statistics from police reports is not
convincing. Although studies based on health care services data found that single-vehicle
accidents make up more than 60 % of injurious cyclist accidents, they lack in-depth
information on the circumstances of these accidents [16]. In this context, the integration of
additional surveys with crashed cyclists increases explanatory power in a very effective manner
[17]. Naturalistic Cycling Studies (NCSs) are another convincing method that was derived from
motor vehicle accident research and recently has been adopted for bicycles [18].
The basic idea of NCSs is to analyse road user behaviour and traffic safety by cameras and
sensors on instrumented vehicles. Main advantages are the availability of records for all events
leading to an accident and the quality of that data as there is no influence due to an artificial
experimental setup [19-20]. One of the first known NCSs with Conventional Bicycles (CBs) was
carried out by Chalmers University of Technology and took place in Gothenburg [19]. The study
found that cycling on poor road surfaces increased the likelihood of experiencing a critical
event – defined as anything that made the cyclist uncomfortable about safety – by the factor
of ten.
This result is supported by another study from Sweden [21] that paired hospital accident data
with specific interviews and found 70% of all severe bicycle injuries being due to single-vehicle
accidents. As a further result of this study, 27 % of those single-vehicle accidents were related
to maintenance and slippery surfaces. Although cycling is partly determined by a country’s
geography and its climate [4], a quarter of cyclists being involved in on-road single-vehicle
accidents in Australian Capital Territory also reported surface characteristics as a contributing
factor to the accident [16]. This includes irregular surface (e.g. cracked surface, potholes, etc.),
wet or slippery surface, loose gravel, sand and debris. In addition to other contributing factors
(carrying extra weight effecting balance, speeding, distraction, and bike failure – multiple
cause could be given) almost three quarters reported losing control of the bicycle as a trigger
for their single-vehicle accident.
A study carried out by German Insurers Accident Research based on hospital accident data
paired with specific interviews confirms these findings [17]. According to this study, there are
two scenario types leading to single-vehicle accidents. The first one – representing around
50 % of all single-vehicle accidents – is due to poor road conditions (mainly at high speeds)
and/or the loss of rider’s balance (mainly at low speeds) and results in a lateral fall of the
5
bicycle. The second scenario is a critical braking situation leading to nose-over (ca. 14 %). Main
reasons are either a defective reaction of the cyclist resulting in an over-braked front wheel or
a front wheel lockup caused by an object such as a sprig. Furthermore, the study states that
the nose-over motion typically occurs in longitudinal direction with less lateral deviation and
mainly at high speed.
2.3 Changes in Mobility Patterns by Electric Bicycles
EBs represent a new dimension for cycling and a rapidly growing market. In the near future,
EBs will cover almost all bicycle segments [3]. When examining EBs’ accident situation, it is
important to begin by distinguishing between e-bikes and pedelecs [20]. On e-bikes, the
auxiliary electric motor operates with a switch or throttle and provides power assistance
without any pedal action. In contrast, pedelecs only give support when the rider is pedalling
[8]. For the latter category of vehicles the Comité Européen de Normalisation (CEN)
implemented the EPAC (Electrically Power Assisted Cycles) standard [22].
One of the largest EB studies to date was undertaken in 2000 by the Centre for Electric Vehicle
Experimentation in Quebec (CEVEQ) [23]. The results suggest that participants perceived the
benefits provided by EBs for utilitarian travel, particularly commuting [8]. Both Parker [24] and
Cherry & Cervero [25] come to similar conclusions. In addition, EBs present a mobility option
for the elderly and those with a physical impairment being unable or finding it uncomfortable
to ride a CB [26-27]. Summarizing, EBs appeal to individuals who otherwise would not ride and
increase frequency of usage and/or range of riding for those currently using a CB [8].
Despite increasing acceptance and usage of EPACs, very little research has been conducted to
assess road safety implications for this emerging vehicle type with possible higher travel speed.
The significant health burden among cyclists due to road accidents, as shown in the
introduction of this paper, raises the question of how safe EBs are compared to CBs. [28-29]
In Germany, EPACs only recently (in 2014) have been included as a separate vehicle category in
the official accident statistics. Reliable accident statistics will therefore not be available before
2017 [30]. For bridging this period, a study of Robert Bosch Company [31-32] selected an
obvious approach. Assuming general behaviour of EPAC users is similar to CB users – justified
with the fact that a normal cyclist is able to reach nearly the same driving performance like a
user of an EPAC if some more muscle power is considered – an extrapolation of the traffic
accident situation involving CBs with comprehensible assumptions respect to EPACs is possible.
The study was based on bicycle accidents in 2009 available in the GIDAS data base. Results
show that in 50 % of the bicycle accidents registered in GIDAS, travel speed will not increase
with EPACs. Main causes were the driving situation (e.g. travel speed higher than supported by
electric auxiliary drive) and the fact that a higher speed with respect to the situation (e.g.
turning) is not realistic. Taking also into account the accident situations in which the bicycle
was hit laterally by a motor vehicle - travel speed was assumed to have no influence – the
study concludes that in most real situations (68 %) an electrical support of the bicycle has no
influence on the accident.
In Switzerland, EBs are explicitly included in official accident statistics since 2011. Initial results
[33] show that cyclists on EBs involved in accidents were mostly 45 - 65 years old. The
evaluation of the injury severity of cyclists on EBs compared to those on CBs led to diverging
results and no clear statement could be drawn.
6
Both studies presented [31-33] are based on official accident statistics and suffer from
underreporting. There are several NCSs investigating vehicle usage, speed and road safety of
EB users. A large-scale NCS carried out by German Insurers Accident Research [30, 34] and
Chemnitz University of Technology [20, 35] gave no evidence that EPAC users are not less safe
or associated with other risks than CB users. Furthermore, results of the study show that riders
on EPACs use the electric auxiliary motor for convenience primarily, which validates the
assumptions in [31-32]. Just like the findings in [33], the study concludes that EPACs are
currently mainly used by elder people, but there are no differences in the number of critical
incidents between EPACs and CBs. Notably, the study points out that EPAC users vary cycling
speed more often than CB users and thus more often find themselves in braking situations.
In addition to this enhanced transient driving behaviour, Chalmers University of Technology
found in their NCS [36, 37] that riders of EBs may become more prevalent in critical areas (e.g.
small hills) and critical periods (e.g. while raining) with limited visibility. Possibly as a
consequence of EBs’ higher travel speed distraction of the cyclists may be particularly
dangerous.
2.4 Representative Survey
Official accident statistics are clearly marked by the disadvantage of an underreporting of
bicycle accidents of unknown magnitude and, apparently, a lack of recent studies that could fill
this gap, which is why we have initiated our own survey.
Thanks to the generous cooperation with the market research and consulting institute YouGov
Germany we have been able to conduct an OMNIBUS survey. The results qualify to be
representative for the German resident population (18+ years old). Founded in London in
2000, YouGov is considered a pioneer in online market research and according to the American
Marketing Association ranks among the top 25 market research institutes in the world.
During summer of 2014 (field work August, 8-11) a representative sample of 1,040 persons had
to answer one or two questions. The first question was:
“If you cycle at least once in a while: Do you remember any crash or bicycle accident within the
last 10 years?”
Following answers were possible - multiple choices were explicitly welcome:
1. Yes, I had a crash/an accident with a normal bicycle that had no electric motor.
2. Yes, I had a crash/an accident with an e-bike.
3. The crash/accident has been reported to the police.
4. No, I cycle but I did not have a bike accident.
5. No, I practically did not cycle within the last 10 years.
The first question was followed by an open question that addresses only those persons, which
remembered a crash/accident with a CB and/or EB (choices 1 or 2 being checked). Accident
cyclists were asked to describe the crash/accident as detailed as possible with no word
restriction. The exact wording of the question reads as follows:
7
“Please describe as detailed as possible, how the accident happened. We are interested in
every detail, specifically the kind of crash/accident (e.g. nose-over, falling over the handlebars,
front wheel skid, etc.), road surface and condition, speed and everything that possibly effected
the braking manoeuvre. Is your bicycle equipped with hydraulic brakes? Did you need to
initiate an emergency braking?”
3 RESULTS
3.1 Representative Outcomes for Germany
The representativeness of the conducted survey allows a discussion of bicycle culture in
Germany. Figure 1 shows 78 % of Germans have driven their bicycle in the last decade. Cycling
was done without an accident by half of the people (49 %). An amount of 93% of those being
involved in an accident (27% of the overall amount) were using a CB and 7 % an EB. Based on
the bicycle stock in Germany (an estimated amount of 72 m), it could be concluded that riders
of EBs have an accident risk higher than riders of CBs (7 % accident risk at 2.9 % EB share in the
total bicycle stock). However, due to the small amount of EB riders involved (N=20), these
findings at best signify a slight tendency, but not a statistically significant finding. It also can be
assumed that EBs are used more often than CB as their number also includes very old bicycles.
Figure 1: Bicycle use and general accident situation
Those respondents with a bicycle accident were also asked if they have reported the accident
to the police. Only 28 of total 304 involved in an accident stated that they did a report. This
results in an underreporting rate of 91 %, which means only one in ten bicycle accidents was
reported by the police (cf. figure 2).
8
In addition to the police reports, all crashed cyclists were asked the second question. 270 of
the 304 answered this question in sufficient detail for further in-depth accident analysis. As a
first result of the content analysis, it was found that 65 % of respondents had a single-vehicle
accident (cf. figure 3).
Figure 2: Underreporting rate of bicycle accidents
Figure 3: Proportion of single-vehicle accidents contributing to all bicycle accidents
9
3.2 In-Depth Accident Analysis
The primary objective of the following in-depth accident analysis is to estimate the possible
benefits of the BDA by quantitative and qualitative statements. For this reason, types, triggers,
and fall events of bicycle accidents are evaluated.
The following figure 4 shows the distribution of accident types for CBs and EBs based on the
exploitable answers of 270 respondents to the second question (equates to 100 %). The type
of accident refers to the transport process which led to the accident. Collision type and
accident cause are not decisive for the determination of the accident type. In accident
research a total of seven groups exists to distinguish accident types [38]. As previously
indicated, the most common group of accident types with a share of around two-thirds (65 %)
are single-vehicle accidents.
Figure 4: Types of accidents (N=270 exploitable bicycle accidents)
Figure 5 illustrates the distribution of accident triggers. Accident triggers can also be objects
such as streetlights or bollards. The accident trigger not necessarily describes the collision
opponent or the main cause but rather the event that actually triggered the accident. For
example, an accident can be triggered by a crossing pedestrian, but the main reason for the
accident is inappropriate speed of the cyclist. In almost half of all accidents (49 %) the main
trigger was a driving error by the cyclist. Remarkably, there is a high proportion (18 %) of other
triggers. Responses open up a broad field from baggage slipped into the spokes to technical
defects such as broken components.
10
Figure 5: Triggers of accidents (N=270 exploitable bicycle accidents)
For the accident specific development of the BDA, the evaluation of fall events is highly
interesting. Figure 6 shows a 39 %-share of both front and rear wheel lockup regarding all fall
events. Loss of balance (25 %), mainly caused by an interference in lateral dynamics,
represents the second largest fall event. Nose-over motion is quantified to 13 %.
The main reasons cited for front wheel lockup were tram rails, curbs and excessive speed in
curves (often linked with strong braking). In the latter case, most riders noted an unfavourable
combination with slippery road surface. Rear wheel lockup mainly happened after over-
braking the rear wheel with subsequent loss of bicycle control. Considering all fall events of
front and rear wheel lockup, it can be stated that the accident severity and frequency of front
wheel lockup is higher. Reasons for nose-over motion can be divided in three groups. In the
first group, the front wheel is blocked by a penetrating object (e.g. sprig). In the second group,
nose-over happens mainly due to braking with low to medium force while riding downhill. The
last group includes events where speeding or distraction of the cyclists followed by an
emergency braking on surfaces with a high coefficient of friction (e.g. dry asphalt) are main
reasons for the accident.
When drawing conclusions for the potential of the BDA, it is important to consider the
proportion of braking. Unfortunately, the answers of the affected riders were not very
meaningful. For this reason, an estimation of braking probability was permitted in the analysis
of the answers. As figure 7 shows, 25 % of the casualties explicitly stated a brake action. In a
further 16 % of all accidents a brake action can be assumed.
11
Figure 6: Fall events (N=270 exploitable bicycle accidents)
Figure 7: Proportion of braking situations (N=270 exploitable bicycle accidents)
12
4 DISCUSSION
4.1 Resulting Impacts of Underreporting
The first research question in this paper focuses on validity and limitations of official accident
statistics based on police, hospital and expert (e.g. German In-Depth Accident Study, GIDAS)
reports. As shown in the beginning of this paper, known studies [4, 10] come to the conclusion
that especially bicycle accidents suffer from underreporting in official statistics. Although
underreporting is a well-known phenomenon, it has not been researched very well. Specifically
when non-fatal injuries are concerned, even to-date cyclists’ injury data should be used and
interpreted with caution.
The study presented in this paper – in the following called “BikeSafe study” – due to its
representativeness for the German population provides a solid base for verifying common
assumptions. As determined in previous studies [11-15], an underreporting rate of 91 %
synonymous to less than 10 % reporting rate of bicycle accidents in official statistics can be
confirmed. Furthermore, a proportion of 65 % single-vehicle accidents on all accidents is
found. This result corresponds to studies presented in [16].
One major advantage of the BikeSafe study is the possibility of an in-depth analysis on types,
triggers and fall events of bicycle accidents. Comparing these results with those from official
accident statistics, the second research question of this paper (“Underreporting of bicycle
accidents and resulting impacts on the proportion of single-vehicle accidents”) can be
discussed. The upper chart in figure 8 shows the impact of underreporting on the distribution
of accident types. It is remarkable that accident types, in which motor vehicles are typically
involved, have a much smaller proportion in the BikeSafe study than in GIDAS. On the other
hand, the significantly higher number of single-vehicle accidents in the BikeSafe study is visible.
This obvious impact of underreporting leads to a completely distorted image when
investigating fall events of bicycle accidents (see lower chart in figure 8). Based on the statistics
derived from GIDAS, an active safety system like the BDA does not seem to be a very effective
measure for improved bicycle safety (share of wheel lockup 3 % and nose-over 1 %). The only
significant advantage of the BDA would be that cyclists lose their fear to use the front brake,
because there is no risk of front wheel lockup or nose-over. The resulting stronger deceleration
of the bicycle could avoid more collisions.
Regarding the findings of BikeSafe study, the potential for a system such as the BDA is much
higher (share of wheel lockup 39 % and nose-over 13 %). Nevertheless, as shown in figure 7, it
is important to remember that only a share of 41 % of all accidents occur while braking.
The following comparison of accident triggers allows an evaluation of different methods in
bicycle accident research. In addition to the statistics based on GIDAS and BikeSafe, the
findings of a study based on hospital data supplemented by additional surveys with crashed
cyclists [17] are plotted in figure 9. Assuming accuracy of the BikeSafe study, investigating
healthcare data with additional surveys seems to be a precise method as well. Despite some
discrepancies (e.g. stationary objects), the results of both studies coincide largely.
13
Figure 8: Comparison of self-determined accident types and fall events
with GIDAS [31-32]
Figure 9: Comparison of self-determined accident triggers
with GIDAS [32] and hospital data [17]
14
4.2 Requirements for the BDA
The available electrical energy and the equipment rate with hydraulic brakes on EBs combined
with the possibility to support the cyclist during deceleration are main ideas of the BDA.
Furthermore, EBs have a more favourable mass and cost ratio than CBs, which makes the
initial introduction of an active safety system for bicycles promising. In addition to clarifying
technical topics such as the influence of the dominant cyclist’s mass on vehicle dynamics,
suspension kinematics of bicycles and largely unknown wheel and tire properties, it is very
important to investigate effects on the current accident situation caused by changes in
mobility patterns due to EBs (third research question) for a target group oriented development
of the BDA.
Results of previous studies on EB users’ behaviour [23-27] point out two main groups:
commuters and the elderly. Furthermore, results show that cyclists use the electric auxiliary
motor primarily for convenience. Despite the anticipated increased accident risk of EBs caused
by e.g. greater travel speed, no uniform picture regarding accident risk can be derived from
accident research studies up to now [30-37]. So far, the only consensus is that higher travel
speed results in a higher injury severity as Nilsson’s power model proves [39]. For this reason,
it was considered at the BikeSafe study that there are no significant changes in mobility
patterns or accident risks due to EBs. Hence, a joint analysis of CB and EB users was possible.
One main objective of the second question in the BikeSafe study was to investigate research
question four, namely cyclist behaviour and accident causation factors with a special focus on
both critical braking situations that should be prevented by the BDA. Unfortunately, it was
found that most of the responses lack in-depth technical details. This is due to
representativeness of the study for the German population. More conclusions than the
qualitative statements listed above could not be derived.
4.3 Future Qualitative Research: Explorations based on qualitative Interviews
Further important tasks primarily concern technical assessment of the effectiveness and
usefulness of active safety systems on bicycles such as the BDA as well as obtaining the main
requirements for the design of such a system.
Detailed narrative interviews with carefully selected respondents will serve as an appropriate
survey method. On the basis of a pre-screening questionnaire we will attempt to find about 20
respondents, who in detail remember a crash/an accident that relates to a brake action.
In comprehensive guideline based interviews (approximately 45 - 60 minutes) the accident
cyclists should describe the course of events during the accident as detailed as possible. We
intend to understand in more detail how the front wheel lockup or nose-over accidents are
caused and how they can be prevented.
In addition, we aim to gain first assessments on the general acceptance of bicycles equipped
with active safety systems such as the BDA. First indications on the willingness to buy and pay
are of particular interest and should be quantified in further research.
15
5 CONCLUSIONS
The main objectives of this paper are to provide both quantitative and qualitative information
to estimate the potential benefits of a BDA and to define future requirements for it. For this
reason, a better understanding of both critical braking situations preventable by the BDA (front
wheel lockup and nose-over) has to be gained. The well-known underreporting of bicycle
accidents in official statistics based on police reports poses a particular challenge. Especially
when investigating single-vehicle accidents, in which both critical braking situations mainly
occur, this phenomenon of underreporting needs to be counteracted by effective and
innovative approaches.
Findings in the BikeSafe study include new valuable representative statements for Germany.
Regarding accidents in accordance with type of bicycle, injured riders were traveling to 27 %-
share with a CB and to 2 %-share with an EB. An accident report to the police was made only in
every tenth case. This results in an underreporting rate of 91 %. The conducted in-depth
accident analysis identified single-vehicle accidents with a share of around two-thirds (65 %) as
the most common group of accident types. A driving error by the cyclist was in almost half of
all accidents (49 %) the main trigger leading to the accident. Regarding the most common fall
event, there was a 39 %-share of both front and rear wheel lockup. Nose-over motion was
quantified to 13 %. It remains remarkable that only a share of 41 % of all accidents occur with
braking.
As a major spin-off of the in-depth accident analysis –assuming accuracy of the BikeSafe study–
it turns out that investigating healthcare data with additional surveys seems to be a very
precise method as well.
6 ACKNOWLEDGEMENT
The authors would like to thank the ministry of education and research in Germany (BMBF) for
sponsoring the project (FKZ 03FH063PX3). Furthermore, the authors thank all academic and
industrial partners for supporting BikeSafe. Finally, the authors would like to thank YouGov
Germany GmbH for supporting the presented empirical study.
REFERENCES
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Brussels, 2013.
[2] ERTRAC, “Safety of vulnerable road users”, in ERTRAC, European Roadmap: Safe Road
Transport, Brussels, 2011, pp. 7-10.
[3] T. Grimaldi, “New urban qualities: Cycling’s (& e-bikes) role in the growing city region”,
International Cycling Safety Conference 2014, Gothenburg, Sweden, 18-19 November
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