STUDY OF THE EFFECT OF TWO-WAY LEFT-TURN LANES ON TRAFFIC ACCIDENTS

The purpose of this investigation was twofold: (a) to determine the safety-effectiveness of two-way left-turn lanes (TWLTLs) and (b) to determine the cost-effectiveness of TWLTLs. The study includes statistical as well as economic analyses. Accident data were collected for 31 roadway sections, 15 five-lane and 16 three-lane sections, for 2 years before and 2 years after the improvements (addition of the TWLTL) were made. Statistical tests were applied on total accidents as well as affected accidents (rear-end, left turn, and sideswipes), their rates, and their severity. Statistically significant reductions were found in accidents, their rates, and their severity. An economic analysis was also performed, including benefit-cost ratios and cost-effectiveness values (cost per accident reduced). The only benefit considered was saving in accidents. The results of economic analysis along with those of statistical analysis indicate that the TWLTL is an economic safety improvement to the conventional two and four-lane urban roadways along which extensive commercial development has taken place.