Risk Factors for Bicycle-Motor Vehicle Collisions at Intersections

      by Alan Wachtel and Diana Lewiston

      In 1992, 722 bicyclists were killed in the United States in collisions with motor vehicles, and an estimated 650,000 people were treated in emergency rooms for bicycle-related injuries It is remarkable that, for a traffic safety problem of this magnitude, so little research has been conducted to establish the causes of these accidents. Instead, design standards for roadways and bicycle facilities, individual project designs, and laws and policies regarding bicycling are based almost entirely on opinion.

      This article reports on a study of bicycle-motor vehicle collisions in the city of Palo Alto, California. The study compares personal characteristics and bicycling behavior-age, sex, direction of travel (with or against traffic flow), and position on the road (roadway or sidewalk) of bicyclists involved in accidents with similar data for the general population of bicyclists observed along the same streets. This comparison enables us to identify factors that are correlated with increased risk of bicycle-motor vehicle collisions.


      This study uses police reports of bicycle accidents in Palo Alto from July 1985 through June 1989. During this period, bicycle-motor vehicle collisions accounted for 314 of 371 bicycle accidents for which a good police report was available (85 percent).

      Accidents at intersections accounted for 237 of 371 total bicycle accidents (64 percent), and 233 of 314 bicycle-motor vehicle collisions (74 percent). We define an intersection as any point where turning or crossing movements are possible for the bicyclist or the motorist. Overtaking accidents, in which a bicyclist in the road was struck from behind by a motorist traveling in the same direction, accounted for only five of 314 bicycle-motor vehicle collisions, and sideswipes for eight.

      The City of Palo Alto's Transportation Division arranged to conduct bicyclist counts in May 1987, including counts at intersections along three major streets on which many bicycle accidents had occurred (92 of 233 bicycle-motor vehicle intersection accidents).

      Bicyclists were counted at nine intersections along three roads. The intersections chosen represented a mix of arterials, collectors, and neighborhood streets; adult commuters, college students, and school children; and on-road bicycle lanes, sidewalk bicycle paths, and roadways without bicycle facilities.

      Nearly 3,000 cyclists were observed during a one-day count of 8 hours at each intersection.

      For each cyclist entering any leg of the intersection, observers trained by the Transportation Division collected data on approximate age (estimated as either 17 years of age and under or 18 and older), sex ,direction of travel, and position on the roadway or sidewalk.

      Data Analysis

      To eliminate as many extraneous influences as possible, the accidents analyzed were restricted to those that took place at intersections along the three arterial streets where the counts were made. Risk is proportional to the accident rate per bicyclist: the lower tbe risk, the lower the likelihood of an accident. For the four major comparisons listed in the Results section, we have also analyzed the data for each corridor independently; we find that, although the risks and risk ratios naturally vary somewhat from corridor to corridor, the same patterns emerge.



      Older bicyclists incur a risk of colliding with a motor vehicle 1.8 times as great as younger ones. This finding was unexpected: we had anticipated that older, more experienced bicyclists would have fewer accidents. We suggest these explanations for our result:

      Few previous studies have allowed for the numbers of bicyclists exposed to accidents in each age group.

      Younger bicyclists may ride more slowly or cautiously, or in larger groups that are more easily seen by motorists.

      The Effective Cycling program then being offered in the Palo Alto middle schools, and other safety measures, may have had a positive influence on the younger bicyclists.


      Although there is a slightly greater overall risk to male bicyclists than to females, this difference is not consistent across subgroups and is not statistically significant.

      Direction of Travel

      All categories of bicyclists traveling against the direction of traffic flow are at greatly increased risk for accidents-on average 3.6 times the risk of those traveling with traffic, and as high as 6.6 times for those 17 and under. This result is readily explained: motorists normally scan for traffic traveling in the lawful direction, so wrong-way traffic is easily overlooked.

      Position on the Road

      The average cyclist in this study incurs a risk on the sidewalk 1.8 times as great as on the roadway. The risk on the sidewalk is higher than on the roadway for both age groups, for both sexes, and for wrong-way travel. The greatest risk found in this study is 5.3 times the average risk for bicyclists over 18 traveling against traffic on the sidewalk.

      Wrong-way sidewalk travel is 4.5 times as dangerous as right-way sidewalk travel. More. over, sidewalk bicycling promotes wrong-way travel: 315 of 971 sidewalk bicyclists (32 percent) rode against the direction of traffic, compared to only 108 of 2,005 roadway bicyclists (5 percent).

      Even right-way sidewalk bicyclists can cross driveways and enter intersections at high speed, and they may enter from an unexpected position and direction-for instance, on the right side of overtaking right-turning traffic. Sidewalk bicyclists are also more likely to be obscured at intersections by parked cars, buildings, fences, and shrubbery; their stopping distance is much greater than a pedestrian's, and they have less maneuverability.


      These results suggest that urban roadway design-not only bikeway design-must take into account that intersections, defined broadly, are the major point of conflict between bicycles and motor vehicles. Separation of bicycles and motor vehicles leads to blind conflicts at these intersections. It also encourages wrong-way travel on sidewalks, paths, and the roadway, further increasing conflicts.

      The aim of a well-designed roadway system should be to integrate bicycles and motor vehicles according to the well-established and effective principles of traffic law and engineering, not to separate them. The goal of integration can be promoted through the use of wide, smooth outside lanes that encourage bicyclists to travel on the roadway rather than on an adjacent sidewalk or path.

      Alan Wachtel is a transportation consultant who has helped develop bicycle plans for several cities and counties in California.

      Diana Lewiston is an Effective Cycling instructor and bicycling-safety author.

      From the League of American Bicyclists Magazine "The American Bicyclist" Nov/Dec 
      1994 Issue. Copyright 1994, League of American Bicyclists. The LAB article is 
      excerpted from the Sept./Oct. 1994 ITE Journal, with permission from the 
      Instititute of Transportation Engineers. 

      The full report can be found in both html and pdf format at the The Bicycling Life

May 2001
Return to: Home