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F-1 APPENDIX F USER SAFETY BENEFITS The prevailing argument is that enhanced facilitiesâbike lanes, bikeways and special intersection modificationsâimprove cyclist safety (83). This claim, however, is the source of a rich controversy within the literature as evidenced by the debate between Forester (57) and Pucher (58). Part of the controversy around this topic is fueled by differences between what cyclists state they prefer (i.e., their perception) and what studies with collision data actu- ally reveal. It is widely acknowledged that increased perception of safety is important to encourage cycling as a means of transportation and re- creation (51, 110). Subsequently, providing separated bicycle facil- ities along roadways is mentioned as a key ingredient in increased perception of safety according to the burgeoning literature related to bicycle related stress factors (111), bicycle interaction hazard scores (112), relative danger index (113), compatibility indexes (114). Existing literature on the safety of bicycle facilities usually con- siders one of three outcome measures: the number of fatalities, the number of crashes, and perceived levels of comfort for the cyclist. Key explanatory variables behind these outcome measures are myriad and complex to identify. For example, the overwhelming majority of bicycle crashes resulting in fatalities are caused by collisions with motor vehicles (104). Less severe crashes tend to occur at intersections or at locations where motor vehicles and bicycles come in contact with each other (105); it is further suggested that crashes are caused by differing expectations between auto drivers and bicyclists (106). However, there is increasing evidence to suggest that some bicycle crashes do not involve any other party (107, 108); this is especially true for children (109). The degree to which perception of safety translates into actual increased safety, however, is still debated. It proves difficult to trans- late perceived measures of safety into quantifiable or economic estimates. Additional confounding factors are that prevailing guide- lines recommend a variety of solutions. For example recent research suggests that both bicycle lanes and wide curb lanes can and should be used to improve riding conditions and safety for bicyclists (http:// www.fhwa.dot.gov/tfhrc/safety/pubs/99035/intro.htm). In the end, bicycle safety data are difficult to analyze, mostly because bicycle trip data (and thus accident probability per trip) are hard to uncover. As more research and conclusive findings become available, it will likely be possible to understand the safety benefits of bicycle facilities in more detailâat such time, a model could then be developed and incorporated into the guidelines.
