Many state and local transportation agencies install nontraversable medians on multilane arterials to improve safety and travel times and to better manage local access. Because nontraversable medians restrict direct left-turn access to and from adjacent developments, traffic destined for these locations must use alternate routes, some of which may involve making U-turns at nearby median openingsa movement often referred to as an indirect left turn. NCHRP Project 17-21, Safety of U-Turns at Unsignalized Median Openings, was conducted to further assess the safety effects of U-turn volumes. This paper presents key findings, along with the access management applications, from that research. It includes a summary of key literature, presents a detailed classification scheme for median openings, summarizes the results of comprehensive field studies, and identifies several highway planning implications.
The research results indicate that access management strategies that increase U-turn volumes at unsignalized median openings can be used safely and effectively. Analysis of accident data found that accidents related to U-turn and left-turn maneuvers at unsignalized median openings occur very infrequently. In urban arterial corridors, unsignalized median openings experienced an average of 0.41 U-turn plus left-turn accidents per median opening per year. In rural arterial corridors, unsignalized median openings experienced an average of 0.20 U-turn plus left-turn accidents per median opening per year. Based on these limited accident frequencies, there is no indication that U-turns at unsignalized median openings constitute a major safety concern.