TRANSPORTATION RESEARCH RECORD 1538
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Bicycle Collisions in Washington State:
A Six-Year Perspective, 1988–1993
RALPH L. WESSELS
A categorical data analysis of collisions between bicycles and motor
vehicles was performed in Washington State using 8,540 collision
records from 1988 through 1993. The collisions were categorized by
action and location of bicyclists and motorists, age groups, road ownership, and county, using a modified version of the Cross/Fisher methodology. Various statistics on demographics, contributing circumstances,
and environmental conditions were developed. The results of the analysis indicate that the type and severity of accidents vary by classification
of roadway and age group and among similar areas within the state.
One-half of the bicycle collisions involved those aged 15 or less. Male
bicyclists were involved in 80 percent of the collisions, which was likely
due to greater exposure instead of a behavioral difference by gender.
Intersections accounted for one-half of the collision locations. The merit
of developing a statewide bicycle-collision report that stratifies information at the local level is presented, along with practical applications
of the data. An inherent bias against safety improvements for bicycles
that is due to collision-reporting thresholds is also discussed.
Traffic-safety improvements have historically been based on collision reports that are submitted to the responsible government
agency and used to identify high-collision and high-severity
locations. As the vast majority of reported collisions involve
motorized vehicles striking objects or other vehicles, most safety
improvements have been directed toward motorized vehicles.
Bicycle collisions have typically not been separated from motorvehicle collisions during the priority-setting process for safetyimprovement projects. Therefore, bicycle-safety improvements
have often been incidental to projects for motor vehicles. This has
resulted in limited safety improvements in bicycle facilities on the
basis of a prioritize need.
To implement a bicycle-safety improvement program and create
a safe bicycling environment, it is necessary to understand why bicycle collisions occur and to identify areas that need improvement. To
assist planners, traffic engineers, safety professionals, bicycle advocates, and others involved in bicycle safety, the Washington State
Department of Transportation (WSDOT) performed a study of
bicycle–motor-vehicle collisions in Washington state. The goal of
the study was to produce a report on collisions between bicycles and
motor vehicles that could be used for promotion of bicycle safety,
assistance in the identification of high-collision areas, discussions
with local agencies and bicycle interest groups on bicycle projects
and programs, and development of safety-management systems. The
study analyzed bicycle collision records for 1988 through 1993 from
the Washington State Patrol (WSP) collision data base. The study
used a modified Cross/Fisher methodology (1) to identify collision
type by geographical area, age group, and road ownership. Other statistical information on bicycle collisions was also provided. The
Transportation Data Office, Planning and Programming Service Center,
Washington State Department of Transportation, 318 East State Avenue,
Olympia, Wash. 98504-7380.
results of the study were published in a report, Bicycle Collision Data
in Washington State 1988 to 1993, hereafter referred to as the Bicycle Collision Report. The information in the report can be used to
develop programs and strategies to improve bicycle safety. Informed
decisions can then be made on how best to address problem. The
methodology used, the results, and the practical application of information contained within the Bicycle Collision Report are discussed.
DATA SOURCE
Collision Reports
Data on bicycle collisions were obtained from the collision records
data base maintained by WSP. A total of 8,540 collision records
were used in the analysis. WSP serves as a depository for all collision records regardless of jurisdiction. In Washington the driver of
any vehicle involved in a collision in which there is injury or death
to any person or $500 or more damage to the property of any one
person is required to submit a traffic-collision report. The form used
by motorists to submit a report is the Motor Vehicle Collision
Report (MVCR). When a collision is investigated by a law enforcement officer, he or she is required to submit a Police Traffic Collision Report (PTCR). There is no statutory requirement for such
investigation that sets a threshold of severity. However, collisions
that result in a fatality and most that result in a disabling injury are
investigated. As the injury severity lessens, the possibility of no
investigation increases. Drivers involved in collisions in which the
property damage is less than the accident-reporting threshold are not
prohibited from filing traffic-collision reports, as specified by the
Revised Code of Washington (Section 46.52.030).
The collision records are derived from both MVCRs and PTCRs.
In the event that one or more MVCRs are received in addition to a
PTCR for a particular collision, only the PTCR is used. It is assumed
by WSP that the PTCR will be more objective and complete.
Approximately 20 percent of all statewide collisions are not investigated by police officers, although this can vary from 10 to 40 percent between counties. For collisions in which only MVCRs are
submitted and there is conflicting information, WSP personnel must
use their judgment to decide what information most accurately
reflects the actual collision. Accordingly, the quality of the data may
vary between localities.
The inclusion of collision records in the WSP data base depends
on whether the collision meets the minimum criteria set forth under
state statute and complies with the Manual on Classification of Motor
Vehicle Traffic Accidents (2). If the criteria are not met, the collision
is excluded from the WSP data base. Among the criteria that would
exclude a collision report from being entered into the data base are
the following:
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• Damage to a vehicle or object did not meet the $500 threshold
and there was no injury or death;
• The point of impact was in a lane or area closed to traffic, (i.e.,
a lane coned off in a construction zone);
• The collision was the result of deliberate intent, such as a suicide or homicide;
• The collision did not occur on a public trafficway, but on private land or a bicycle path; or
• The collision did not involve a motor vehicle.
TRANSPORTATION RESEARCH RECORD 1538
1990 and Burien and Woodinville in 1991. The city of Winslow
became the city of Bainbridge Island in 1991 and annexed the entire
island. The average distance for each of the five functional classifications of roadways during the study period was 1,228 km (763 mi),
for the Interstate system, 10,026 km (6,227 mi), for all state routes,
66,939 km (41,577 mi), for county roads, 18,710 km (11,621 mi),
for city streets, and 32,706 km (20,314 mi) for other roads.
Demographic Data
These criteria exclude many bicycle collisions from being entered
into the WSP traffic-collision data base even if a collision report has
been submitted. Previous studies have indicated that a high percentage of bicycle collisions that are eligible to be reported are not; estimates have ranged from approximately 10 to 50 percent (3,4). For a
bicycle to be considered for inclusion in the traffic-collision data base
the collision must first involve a motor vehicle. If the location of the
collision was on a nonpublic trafficway such as a bicycle path, the
accident would be excluded from the data base. If there was no injury
or death but the collision involved a motor vehicle on a public thoroughfare, then the property damage of any one person would have to
have been $500 or more. Given the disparity in mass between a
motor vehicle and a bicycle, a bicycle is more likely to suffer significant damage in a collision. Many bicycles do not meet the threshold
value of $500, particularly those ridden by youths. Therefore, many
collisions reported because of property damage only are excluded
from the data base. It should not be surprising that 98 percent of collisions within the data base involve either injury or death.
Collisions involving tricycles (35 total) and unicycles (4 total)
were not included in the study. Although adult tricycles are occasionally used for transportation, it was presumed that most tricycles
and unicycles are primarily used as toys or for entertainment instead
of transportation. Therefore, the behavior of the operator of a tricycle or unicycle may not typify that of a bicyclist.
Helmet-Law Enactment
Washington State has not enacted a law requiring bicycle-helmet
use. Two jurisdictions did enact mandatory-bicycle-helmet laws
during the study period. The King County Board of Health adopted
a helmet law for all of King County, with the exception of the City
of Seattle, on March 4, 1993. The area affected in King County contained a population of 991,060. The city of Port Angeles (population 17,710) adopted a helmet law on May 18, 1993. There has been
very limited enforcement of the helmet laws since their adoption.
The primary effect of these laws has been to encourage helmet use.
Because the helmet laws were adopted near the end of the study
period, and because less than 20 percent of the state population
resides within these areas, the effect on the results of the study were
expected to be minor.
Roadway Jurisdictional Changes
During the study period the number of kilometers of road for the five
functional classes of roadways changed. The change was caused by
the addition of roads, a change in road jurisdiction, and road closures
such as restricted access on U.S. Forest Service roads. Four cities
were added during the study period: Federal Way and SeaTac in
Data from the 1990 census were used without adjustment for population increase or change in demographics. Although not totally
accurate for mathematical calculations, it was decided that the 1990
census data would best represent the average demographics of the
geographical areas within the state for the study period.
ANALYSIS METHODS
Collision types were categorized using a modified version of the
Cross/Fisher bicycle-collision classification method. The Cross/
Fisher methodology classifies bicycle and motor-vehicle collisions
in 36 categories on the basis of vehicle action and location (1). The
goal of the study was to use as many of these categories as possible.
Modification of the categories was necessary because the data fields
in the WSP data base were not completely compatible with the
Cross/Fisher method and because of the high number of records
used in the analysis. In some cases, a single modified Cross/Fisher
category could be developed from several similar Cross/Fisher
categories. The modified Cross/Fisher method was capable of
classifying collisions in 22 categories.
Statistical analysis software was used to develop arguments that
would use the data fields to classify collisions into modified
Cross/Fisher categories. The collision categories were then used for
different subsets of the data to develop cross tabulations.
Functional class of roadway was selected for the primary stratification in Tables 1 through 5. The five functional classes of roadways were interstate, state routes, county roads, city streets, and
other roads. No distinction is made in this analysis between a bicycle collision on the mainline, a ramp, or a crossroad of the Interstate
or a state route system. The other roads classification includes roads
owned by state parks, universities, correctional facilities, the U.S.
Forest Service, and the National Park Service, as well as other government roads not included in the first four classes. A table of collisions for other roads was included in the original study but is
excluded from the discussion because of the low number of collisions (a total of 33). Cross tabulations of injury collisions, fatal
collisions, and age group were performed for the modified
Cross/Fisher classifications for each functional class of roadway.
The seven age groups used in the Bicycle Collision Report were (a)
less than 5; (b) 5 to 9; (c) 10 to 15; (d) 16 to 24; (e) 25 to 34; (f) 35
to 54; and (g) 55 or older. The 55-or-older age group (2.2 percent)
had similar characteristics to the 35-to-54 age group (9.4 percent).
The 35-to-54 and 55-or-older age groups have been combined in
Tables 1 through 6.
Cross tabulations of the modified Cross/Fisher classifications
by injury collisions, fatal collisions, and functional class of roadway were also performed for each of the 39 counties in Washington State. This was intended to assist in the identification of the
Wessels
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TABLE 1 Washington Bicycle Collisions 1988 to 1993—All Roads
type of collision by road ownership and to allow statewide comparison.
Descriptive statistics were prepared for the study and presented
in graphical format. Portions of these statistics are shown in Figures
1 through 5.
RESULTS
Number of Reported Collisions
Bicycle use is seasonal in Washington, with the majority of collisions occurring between April and October. Most collisions occur
on weekdays between 3:00 p.m. and 8:00 p.m. Caution must be
used in the use of annual collision data in determining trends
because the number of collisions is related to exposure to the
potential for collisions. Collision exposure varies from year to year
and is influenced by such factors as population growth, the number of bicyclists, the number and length of trips made, the development of bicycle facilities, roadway-safety improvements, and
weather. For instance, the decrease in bicycle collisions from 1992
to 1993, as shown in Figure 1, may have been caused by the difference in the weather (1993 had a high number of rainy days during the summer months), not a behavioral change among bicyclists
and motorists or an increase in safer facilities for bicyclists. The
enactment of helmet laws in King County and Port Angeles and
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TRANSPORTATION RESEARCH RECORD 1538
TABLE 2 Washington Bicycle Collisions 1988 to 1993—Interstate
the promotion of helmet use by bicycle clubs, civic groups, and the
Helmet on Wheels program may also have had an effect. As a general trend, reported bicycle collisions have demonstrated a continual annual increase.
Demographics
Gender
Males accounted for 54 percent and women for 37 percent of the
drivers of motor vehicles involved in bicycle collisions. Gender was
not indicated in the other 9 percent. Males accounted for 80 percent
of all bicyclists involved in collisions. Some studies have indicated
that the high percent of male bicyclists involved in collisions may
be due to the tendency of males to be greater risk takers (5,6). Others
have speculated that the higher percentage of males reflects a greater
amount of exposure to potential collisions (3). If males are in fact
greater risk takers, then a greater percentage of males should
become fatalities or experience more severe injury compared with
females. Figure 2 shows that both male and female populations
experience similar percentages of fatalities and injury severity.
Therefore, it can be concluded that male bicyclists are involved in
more collisions than females because they have higher exposure, not
because of a behavioral difference.
Age Group
Approximately 50 percent of all collisions occurred in the population aged 15 or less. The greatest portion of those occurred in the
population aged 10 to 15. The percentages for each age group are
Wessels
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TABLE 3 Washington Bicycle Collisions 1988 to 1993—State Routes
shown in Table 1. Figure 3 shows the collision rates per 10,000 population per year on the basis of age groups. Data on exposure rates
that could be used for statewide analysis are unavailable in Washington. Therefore, collision rates based on population presently
offer the best reliability for trend analysis and identifying target populations for safety programs. Bicyclists between 10 and 15 years old
demonstrated almost double the collision rate for the next highest
age groups of 5 to 9 and 16 to 24. Accordingly, it appears that safety
programs would be most effective by targeting bicyclists aged 34 or
less, with an emphasis placed on bicyclists aged 15 or less. The high
number of male bicyclists involved in collisions may further identify a target population.
Figure 4 shows the number of fatal or disabling collisions for each
age group by road type. Of note is the relatively high number of seri-
ous collisions for the age groups 5 to 9 and 10 to 15 that occur on
county roads. Very few serious collisions occurred on state routes
for those younger than 10.
Other Factors
Most (82 percent) of the reported bicycle collisions occurred during
daylight. Daylight bicycle collisions were slightly less severe than
those in twilight or darkness. The weather was either clear or cloudy
for 92 percent of collisions involving bicycles. Alcohol involvement
was similar for both motorists and bicyclists. Approximately 1 percent of motorists and of bicyclists had been drinking in all reported
bicycle collisions. For fatality collisions this percentage increased
to 9 for motorists and 11 for bicyclists.
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TRANSPORTATION RESEARCH RECORD 1538
TABLE 4 Washington Bicycle Collisions 1988 to 1993—County Roads
Location of Collisions by Functional Class of Roadway
All Roads
City streets are the location of the majority of collisions, followed
by county roads and state routes. A comparison between the location of all collisions and the location of fatal collisions is shown in
Figure 5. The percentage of fatal collisions by road type does not
correspond with the percentage of total collisions. Figure 5 shows
that although 65 percent of the accidents occurred on city streets,
only 33 percent of the fatalities occurred there. County roads were
the location for only 21 percent of all collisions, but 45 percent of
all fatalities. State routes and Interstate highways, respectively, were
the locations for 13 and 1 percent of all collisions, but 18 and 4 percent of the fatalities. This indicates that roads with higher driving
speeds are the locations of more fatalities proportional to the overall number of accidents.
Of particular interest is the location or action involved in the
majority of bicycle collisions. Table 1 shows that 49 percent of collisions occurred at intersections, 16.7 percent occurred where a bicyclist entered or left the roadway at a midblock location, and 14.5 percent involved a bicyclist riding the wrong way. A common
perception is that the most frequent type of bicycle collision
involves a bicyclist being struck from behind by a motor vehicle, but
it accounted for only 5.7 percent of all collisions. Turning or swerving action by a bicyclist (not at an intersection) accounted for
Wessels
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TABLE 5 Washington Bicycle Collisions 1988 to 1993—City Streets
5.7 percent of all collisions, with most of these bicyclists belonging
to the 5-to-9 or 10-to-15 age groups. It should be noted that bicyclists hit from behind by a motor vehicle and bicyclists turning or
swerving represented approximately 12 percent of all collisions, but
40 percent of all fatalities.
The percentages for the different bicycle-collision types in Washington State closely correlated with data from the National Highway
Traffic Safety Administration and the Oregon Department of Transportation (ODOT). From national data, the five most common factors involved in bicycle fatalities are failure to yield (23 percent),
improper crossing of roadway or intersection (15 percent), failure to
obey traffic control devices (9 percent), failure to keep in proper lane
(8 percent), and operating without required equipment (5 percent)
(7). ODOT reported in 1992 that the five primary collision types
were intersection (48 percent), bicyclist riding against traffic
(15 percent), motor-vehicle entering or leaving at midblock (12 percent), bicyclist entering or leaving at midblock (11 percent), and
bicyclist swerving (5 percent) (8).
Interstate System
Washington is one of a handful of states that allows bicycles on
interstate roadway shoulders. (The state excepts urban areas with
high traffic volumes.) The results shown in Table 2 indicate that few
bicycle collisions occur on the Interstate system. Of those, approximately 60 percent are intersection related and likely occurred at
crossroads or ramp-gore areas. More than 22 percent involved a
bicyclist going the wrong way. However, this statistic could be
skewed because so few collisions were reported.
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TRANSPORTATION RESEARCH RECORD 1538
TABLE 6 Washington Bicycle Collisions 1988 to 1993—Thurston County
FIGURE 1
Bicycle collisions by year.
FIGURE 2
Bicycle-collision severity by gender of bicyclist.
Wessels
FIGURE 3
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Bicycle-collision rate per 10,000 population per year.
FIGURE 5
All collisions versus fatal collisions by location.
State Routes
City Streets
Bicycle collisions on state routes, other than the Interstate system,
are shown in Table 3. Intersection collisions accounted for approximately 45 percent of bicycle collisions on state routes. Bicyclists
riding the wrong way accounted for a significant 21 percent of collisions. Half of the fatalities involved the bicyclist turning or swerving at a location that was not an intersection.
The majority of bicycle collisions occurred on city streets and are
shown in Table 5. Most of the fatalities on city streets occurred at
intersections. In contrast to county roads, motorist action at intersections accounted for a high 30 percent of the total bicycle collisions on city streets.
County Roads
Thurston County
County roads, as shown in Table 4, accounted for the highest percentage of bicyclists being struck from behind by motor vehicles of
any functional classification of roadway. The percent of bicyclists
turning or swerving was almost twice that of all roads. The higher
percentage of these types of collisions is likely a result of narrower
lane widths, shoulders that were inadequately paved for the accommodation of bicyclists, and poor sight distance at many locations on
county roads. Most of the fatalities that involved a bicyclist entering or leaving a roadway at a midblock location occurred on county
roads. Motorist action at intersections accounted for a surprisingly
low 15 percent of the total bicycle collisions on county roads. A
higher than average percentage of collisions involved bicyclists 15
years old or less.
For illustrative purposes, bicycle collisions statistics for Thurston
County (population 161,238) are shown in Table 6. Thurston
County contains each of the five functional classifications of roadways. Olympia is the state capital, the county seat, and is home to
Evergreen State College. Bicycle use is relatively high because of
the number of college students. Two one-way streets provide major
access through Olympia’s downtown and to residential and business
areas to the east. Several cities—Olympia, Lacey, and Yelm—have
constructed bicycle lanes within their city limits. Bicycle use is prohibited on the I-5 through Olympia and the adjacent cities of Lacey
and Tumwater.
Of particular interest in Thurston County is the relatively high
percentage of bicycle collisions involving bicyclists riding the
wrong way compared with the statewide average and counties of
similar population. Most collisions occurred on city streets. It would
appear that an effective means to reduce bicycle collisions in
Thurston County would be an education and enforcement campaign
to change the behavior of bicyclists.
APPLICATIONS FOR BICYCLE COLLISION DATA
Tool for Decision Makers
FIGURE 4 Bicycle fatality or disabling injury versus age group
by road type.
The Bicycle Collision Report provides a wide range of information
that can be examined by location, age group, collision type, and road
ownership. The report has become a key component of WSDOT’s
nonmotorized Safety Management System (SMS) and provides
SMS members with an overview of statewide bicycle collisions. It
provides detailed information to local traffic engineers, law enforcement personnel, and educators. The report also assists local officials
in developing countermeasures for bicycle collisions occurring in
their areas.
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Bicycle collision data can demonstrate that engineering may not
be the most effective means of reducing bicycle collisions. Depending on the types of collisions in an area, the most effective means of
reduction may be through education of motorists and bicyclists
combined with enforcement. Bicycle-collision information can also
be used as a safety management tool, one which becomes particularly useful if collisions are stratified at the local (county) level so
that problems can be identified by ownership of road.
The Bicycle Collision Report has been useful for educating decision makers on bicycle issues. Many decision makers and others in
transportation have developed perceptions about bicycling based on
personal experience instead of accurate information. The ability to
immediately respond to spontaneous questions or misconceptions
with accurate data is beneficial in the development of bicycle programs. A decision maker recently postulated that bicyclists would
be safer if they rode against traffic. He was surprised to learn that in
Washington the number of bicycle collisions in which a bicyclist
was riding the wrong way is two and one-half times the number of
collisions in which a bicyclist was struck from behind by a motor
vehicle. The statistic was followed with an explanation of why this
occurs. The ability to respond with accurate statistics can help to dispel inaccurate perceptions.
Specific Applications
The Bicycle Collision Report has been useful in responding to local
concerns. In one rural county concerns were raised about the safety
of bicyclists using the scenic state highway that is the main route
through the county. The county’s economy is based on timber and a
growing recreational industry. Local officials, citizens, and the local
newspaper expressed their concern about safety because the number of bicyclists in the area was increasing. The primary concern
was that bicyclists would be hit from behind by overtaking vehicles,
particularly by logging trucks and recreational vehicles. Another
concern was that traffic would be forced into the opposing lane to
pass bicycles on sections with narrow or no shoulders, creating a
hazardous condition. In reaction to these concerns the local officials
requested that WSDOT ban bicycles from the state highway.
Information from the Bicycle Collision Report was used to
analyze the situation. The data in the report indicated that four
bicycle–motor-vehicle collisions had occurred in the county over
the 6-year study period. Only one of these collisions was on the state
highway, and it was related to an intersection at which the bicyclist
failed to yield. A more extensive examination of the collision
records for the previous 20 years indicated this was the only collision on the section of state highway within the county. A check of
emergency medical service records for the previous 3 years (the
limit of the system’s historic records) indicated only five cases of
injuries to bicyclists within the county, two of which occurred on
county roads, two at private residences, and one at an unknown location. The concerns of the local officials were resolved by presenting
information to show how few bicyclists actually were involved
in collisions in the county and to demonstrate that incidents of
bicyclists being struck from behind were statistically rare.
TRANSPORTATION RESEARCH RECORD 1538
CONCLUSION
Collision reports can be an effective means of identifying types of
bicycle and motor vehicle collisions. A statewide bicycle-collision
report can be used effectively in the development of a bicyclesafety-management system and strategies to improve bicycle safety.
A report that indicates the type of collisions occurring in local areas
by roadway classification and age groups would assist planners, traffic engineers, safety professionals, bicycle advocates, and others
involved in bicycle safety to understand why bicycle collisions
occur and to identify areas of needed improvement. Because local
officials and citizens may have concerns even in areas where few
bicycle collisions have occurred, data that demonstrate a lack of
collisions are also useful.
Type of collision varies among different road classifications and
age groups of bicyclists. Type will also vary by area within a state
because of the behavior of bicyclists and motorists, the types of
roadways, the presence of bicycle facilities, and exposure rates. The
exposure rate of a bicyclist, instead of gender, appears to be a
causative factor in bicycle–motor-vehicle collisions. Male and
female bicyclists have similar rates of injury severity within their
populations.
The threshold requirements for reporting vehicle collisions
exclude a majority of bicycle collisions from collision data base
records. This is primarily because of the requirements of motorvehicle involvement, minimum $500 damage, and exclusion of bike
paths. Safety-improvement programs that only use motor-vehicle
collision records to determine safety improvements are inherently
biased against bicycles as a transportation mode. A change in the
reporting requirements for bicycle collisions is necessary to allow
problem areas to be better identified and safety improvements to be
specifically targeted toward bicycles.
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Inc., Santa Barbara, Calif., 1977.
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Classification of Motor Vehicle Accidents. Report ANSI D16.1-1989.
National Safety Council, Oct. 2, 1989.
3. Rivara, F. P. R. Soderberg, P. Miller, and K. Allen. Pedestrian and Bicycle Collisions With Motor Vehicle in King County. The Harborview
Injury Prevention and Research Center, and King County, Wash., 1991.
4. Stutts, J. C. Analysis of Bicycle Accident Data from Ten North Carolina
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Publication of this paper sponsored by Committee on Bicycling and Bicycle
Facilities.