Sidepath Safety Model: Bicycle Sidepath Design Factors Affecting Crash Rates

The Florida Department of Transportation has sponsored a project to create a method for determining what bicycle facility types provide the best mobility for bicyclists. This project includes, as a component, developing a model that predicts the relative bicycle and motor vehicle crash rates between on-street facilities and shared-use paths located adjacent to a roadway (sidepaths). This paper describes how this sidepath safety model was developed and how it provides important guidance for bicycle facility type selection and sidepath design. The model was developed using operational and geometric data, user counts, and crash data for 21 roadway sections throughout Florida. Four determining factors were found to be significant and are included in the model: sidepath width (possibly a surrogate for user speed), separation of the sidepath from the roadway, posted speed of the roadway, and number of lanes on the adjacent roadway. The sidepath safety model R² value is .81. The sidepath safety model also serves to quantify some of the concerns expressed in the AASHTO Guide for the Development of Bicycle Facilities. Using this model, transportation planners and engineers will be able to test alternative design treatments to find the safest one for bicyclists. They will also be able to review existing sidepaths that have crash problems to identify potential solutions. This model provides an important new tool for transportation professionals to use when deciding on and designing bicycle facilities.