Safety impacts of edge lines on Texas rural two-lane roadways
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Roadway crashes are a detriment to our society, so improvements in roadway safety that reduce crashes are of extreme importance. Though it is clear that crashes on our highways are a drain both socially and economically, the contribution of roadway safety to overall community safety is difficult to quantify and has seen many approaches. The study first defines highway safety as a whole, and then focuses on safety improvements on rural two-lane roadways. One such improvement, highway edge lines, may be especially beneficial on such highways. A literature review indicated that edge lines may have a tendency to reduce accident experience on rural, two-lane roads and may affect vehicle speed and lateral position in the lane, which in turn may increase or decrease accident likelihood. After compilation of a database of rural, two-lane roadways in Texas, an accident analysis comparing such roadways with and without edge lines was performed. In addition to general accident frequency analysis taking into account varying traffic lane and shoulder widths and roadway curvature, factors such as accident type, intersection presence, light condition, surface condition, crash-supporting factors, severity, driver age, and driver gender were considered. Further, stationary roadside observations measuring vehicle speed and lateral position were taken during daylight and darkness on three rural, two-lane roadway test sites first without edge lines, and then again after the sites were striped with edge lines. Overall, the accident analysis showed that edge line treatments on rural two-lane roadways may reduce accident frequency, especially run-off-the road frequency, with the highest impact on curves and narrow roadways. The stationary observation analysis indicated some tendency of edge lines to increase vehicle speeds and also decrease speed variations, while moving vehicles toward the pavement edge on narrow roadways, especially at night.