Bicycle Collisions in Washington State: A Six-Year Perspective,

Transcription

1 TRANSPORTATION RESEARCH RECORD Bicycle Collisions in Washington State: A Six-Year Perspective, 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 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 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 ). 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:

2 82 TRANSPORTATION RESEARCH RECORD 1538 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. 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, 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, 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 1990 and Burien and Woodinville in 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 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

3 Wessels 83 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

4 84 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

5 Wessels 85 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.

6 86 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

7 Wessels 87 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.

8 88 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.

9 Wessels 89 FIGURE 3 Bicycle-collision rate per 10,000 population per year. FIGURE 5 All collisions versus fatal collisions by location. State Routes 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. City Streets 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 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. Thurston County 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.

10 90 TRANSPORTATION RESEARCH RECORD 1538 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. 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. REFERENCES 1. Cross, K. D., and G. Fisher. Identification of Specific Problems and Countermeasure Approaches to Enhance Bicycle Safety. Anacapa Sciences, Inc., Santa Barbara, Calif., Committee on Motor Vehicle Traffic Accident Classification. Manual on Classification of Motor Vehicle Accidents. Report ANSI D National Safety Council, Oct. 2, 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., Stutts, J. C. Analysis of Bicycle Accident Data from Ten North Carolina Hospital Emergency Rooms. University of North Carolina Highway Safety Research Center, Chapel Hill, Rodgers, G. B. Bicyclists Deaths and Fatality Risk Patterns. Accident Analysis and Prevention, Vol. 27, No. 2, 1995, pp Gårder, P. Bicycle Accidents in Maine: An Analysis. In Transportation Research Record 1438, TRB, National Research Council, Washington D.C., Oct. 1994, pp Traffic Safety Facts NHTSA, U.S. Department of Transportation, April Bicycle/Motor Vehicle Accident Summary. Oregon Department of Transportation, Publication of this paper sponsored by Committee on Bicycling and Bicycle Facilities.