Assessing Safety Performance on Urban and Suburban Roadways of Lower Functional Classification: A Comparison of Minor Arterial and Collector Roadway Segments

Abstract

Previous research of urban roadway safety performance has generally focused on roadways of high functional classifications, such as principal arterials. However, roadways with lower functional classifications, including minor arterials and collectors, typically possess characteristics that differ from those of higher roadway classes. Therefore, assumptions made on the general effect of the predictor variables from typical safety performance functions may not apply to lower roadway classes. To address these knowledge gaps, a safety performance evaluation of urban/suburban minor arterial and collector roadway segments was performed using traffic and roadway data along with eight years of crash data from 189 miles of two-lane urban and suburban roadways in Washtenaw County, Michigan. Mixed-effect negative binomial models with segment-specific random intercept were developed for minor arterial and collector road segments, considering total, fatal+injury, and property damage only crashes. In general, minor arterial roadways showed greater crash occurrence compared to collector roads. Posted speed limit had a significant positive association with crash frequency, and this effect increased when the speed limit exceeded 40 mph. The effect of speed limit was stronger on minor arterial segments and for fatal+injury crashes. Additionally, driveway density was found to have a significant effect on safety performance, which was stronger for commercial/industrial driveways compared to residential driveways and for collector roads compared to minor arterials, particularly when considering residential driveways. On-street parking was associated with lower crash occurrence, with a stronger effect on collector roadways, likely due to greater parking turnover when compared to minor arterials.