Safety Improvement from Edge Lines on Rural Two-Lane Highways

The previous study Impact of Edge Lines on Safety of Rural Two-Lane Highways completed in 2005 concluded: with edge lines, centralization of vehicles’ positions is more apparent during night time, which reduces the risk of run-off road (ROR) and head-on collisions, and edge line markings generally cause drivers to operate their vehicles away from the road edge, irrespective of the roadway alignment. Does the changed vehicle lateral position reduce the frequency of crashes? Answering this question is important to Louisiana Department of Transportation and Development (LADOTD) since implementing and maintaining edge lines on narrow two-lane highways require significant resources from LADOTD. More than 40 percent of rural, two-lane highways in Louisiana has a pavement width (excluding shoulders) less than 22 ft with no edge lines. Thus, the goal of this project was to investigate the safety impact of edge lines on narrow, rural two-lane highways in Louisiana by analyzing crash frequencies before and after edge line implementations on a group of selected narrow, rural two-lane highways from all LADOTD districts. Using the latest safety analysis statistical method, this project analyzed the crash data before and after edge line implementation and concluded that: placing pavement edge lines on rural two-lane highways in Louisiana can not only change vehicles’ lateral positions but also reduce crashes. The crash modification factor (CMF) for edge line on narrow, rural two-lane highways is 0.78. Considering the decreasing trend in crashes in the state for the past three years, the modified CMF is 0.83, which implies that, on average, implementing edge lines can reduce 17 percent of crashes.