United States Department of Transportation
i
Developing Crash Modification Factors for Bicycle-Lane Additions While Reducing Lane and Shoulder Widths
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2021-07-01
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[PDF-1.18 MB]
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Abstract:This project evaluated bicycle-lane additions when reducing lane and shoulder width as a safety-improvement strategy (also known as a safety intervention). Crash modification factors (CMFs) and benefit–cost (B/C) ratios were estimated for total, fatal and injury, and property-damage-only (PDO) crashes. Researchers studied facilities that included urban two- and four-lane arterials, collectors, and local roads in Washington and Texas. The study design was cross sectional and included sites without bicycle lanes but with similar characteristics to sites with bicycle lanes. The research team applied propensity score methods on data collection and in statistical analyses to improve the balance between treated and comparison sites. Results for Washington suggested reductions for fatal and injury (0.772 CMF, statistically insignificant) and PDO (0.885 CMF, statistically insignificant) crashes, but the small sample size resulted in large uncertainties for these estimates. Results for Texas were consistent with the directions and magnitudes of the Washington analysis. In contrast, the larger dataset from Texas yielded CMF estimates with statistical significance at the 95-percent confidence level. From the Texas analysis, this research found that statistically significant CMFs for total and PDO crashes ranged between 0.514 and 0.734, depending on facility type and bicycle volumes. All CMFs for fatal and injury crashes were statistically insignificant (ranging between 0.530 and 1.58, depending on facility type and bicycle volumes), as were CMFs for total crashes (ranging from 0.558 to 0.901, all statistically insignificant). The B/C ratio estimated for Texas two-lane undivided urban collectors and local streets was 16.61, assuming the average daily bicycle traffic did not increase after the installation of bicycle lanes.
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