Assessing the Effect of Paved Shoulder Width on Road Traffic Crash Risk on a Six-Lane Rural Highway in India

This study aims to assess the safety effect of the paved shoulder width of a 175-km six-lane rural highway in India. First, the applicability of the matched case-control (C-C) method in the case of highway segments with multiple crashes was assessed. Second, the safety effectiveness of the paved shoulder and other risk factors were evaluated using the matched C-C method. Three scenarios with different case definitions were developed using the matched C-C method and ordinal logistic regression. The study used 100-m segment-specific speed, volume, geometrics, roadside characteristics, and fatal crash data between 2016 and 2018. Developed scenario results suggested that the matched C-C method can assess crash risks on segments with multiple crashes by defining cases separately or considering the number of crashes as an ordinal variable. Results also suggested that the probability of observing crashes increases as paved shoulder width increases. However, the probability of observing multiple fatal crashes decreases for wide paved shoulder width increases. The safety effectiveness of paved shoulder width assessment showed that a wide paved shoulder had a higher risk of a fatal crash than a paved shoulder width of 1.0 to 1.5 m. The segments with unpaved shoulders were unsafe compared to segments without them. These results can be used to prepare guidelines by road-owning and construction agencies to adopt safe paved shoulder widths for six-lane and multilane highways in India. Results may also support the development of a new highway design policy concerning preferable safe paved shoulder width for multilane greenfield highways in India.