As part of research conducted to develop a more definitive guidefor the selection of divided and undivided sections on urban four-lane roadways in nebraska, accident experience at signalized and unsignalized intersections on urban four-lane roadways was analyzed to assess the safety effects of left-turn lanes. Results of this analysis are presented. Multivehicle accidents on intersection approaches with left-turn lanes were compared with those on similar approaches without left-turn lanes. The degree to which left-turn lanes on signalized and on uncontrolled approaches reduced accidents was computed.The statistical significance of the percent reductions was determined using the chi-squared test. Left-turn lanes at intersections on urban four-lane roadways were found to significantly reduce rear-end, sideswipe, and left-turn accidents. However, on the uncontrolled approaches of intersections on urban undivided roadways, left-turn lanes were found to significantly increase right-angle accidents, as well as reduce rear-end, sideswipe, and left-turn accidents. This paper appears in transportation research record no. 1239, Geometric design and operational effects.
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