Safety Effectiveness of Lane and Shoulder Width Combinations on Rural, Two-Lane, Undivided Roads

Abstract

There is a need to evaluate low-cost safety strategies that states may implement as part of their Strategic Highway Safety Plan. FHWA organized a pooled fund study of 26 states to evaluate several low-cost safety strategies, including the reallocation of total paved width. This study identifies whether it is safer to increase lane width or increase shoulder width given a fixed total width. Geometric, traffic, and crash data were obtained for more than 52,000 mi of roadway in Pennsylvania and Washington State. A case-control approach was applied to evaluate the safety effectiveness of various lane–shoulder configurations. There was a general reduction in the odds ratio as total paved width, lane width, and shoulder width increased individually; this is consistent with previous research. However, the primary research objective was to estimate the safety effectiveness of reallocating a fixed total paved width. Individual state results did not indicate a clear trade-off between lane and shoulder width for a fixed total width. Supplementing the results of this study with previous research, crash modification factors (CMFs) are provided for several lane–shoulder combinations. The selected values present a more apparent trade-off, indicating a slight benefit to increasing lane width for a fixed total width. Importantly, the results differ from other studies that developed CMFs without considering the interaction between lane and shoulder width, including those studies currently referenced in the Highway Safety Manual. This raises the question of whether CMFs should reflect the interaction between lane and shoulder width.

Developing crash modification functions to assess safety effects of adding bike lanes for urban arterials with different roadway and socio-economic characteristics

“…This may be because drivers are more aware of bicyclists on the bike lane (Sadek et al, 2007) and drive more cautiously to avoid collision with bicyclists when the lane width is narrower. In fact, the safety effects of the roadways with narrow lane width can be higher than the roadways with wide lane width for specific roadway conditions (Mehta and Lu, 2013;Gross et al, 2009).…”

Multivariate Poisson-Lognormal Model for Analysis of Crashes on Urban Signalized Intersections Approach

“…Signal coordination decreases vehicle stop-and-go and thus decreases the potential of rear-end crashes. In addition, this study focuses little on the interactive influences of various factors, but the combinations of geometric characteristics may show better prediction results (Gross et al 2009). However, the interactive effects of variables may make the model more complex and difficult to explain.…”

Engineering Solutions to Enhance Traffic Safety Performance on Two-Lane Highways

“…Their findings showed that the radius and length of each horizontal curve significantly influenced the frequency of crashes. Gross et al [5,6] and Schrock et al [7] explored the use of observational data to estimate safety effectiveness for changes in lane and shoulder width and found that adding passing lanes was an economical and effective safety improvement for rural two-lane highways. These findings can be used to help determine cost-benefit ratios to compare competing alternatives.…”