Evaluation of Operations, Fuel Consumption, and Emission at Signalized Intersections Replaced by U-Turns along Six-Lane Highways

U-Turns are an important and unconventional tools for the improvement of highway operations. In some cities of Iran, signalized intersections were replaced by mid-block median u-turns which have different design from foreign counterparts. Recent studies on the performance of u-turns led to controversial results since they did not apply systematic approach for accurate evaluation, studies were not conducted for peak and nonpeak periods, and the resultant effects of eliminating delays at the intersection and spending more time for making a u-turn were not considered simultaneously. Therefore a research was conducted in which operations of signalized intersection were simulated and operational models were deployed to obtain travel times and speeds at u-turns. At high and medium volumes, u-turns increase travel speed of vehicles by 20 (km/h) and decrease speed by 10 (km/h) at low volumes. As the volume ratio of turning vehicles to highway through vehicles rises, u-turns ability to improve highway mobility rises. At Bagheri-Golbarg and Bagheri-Resalt intersections (in Tehran), fuel consumption declines by 1,623 and 4,244 liters per day, although minor street vehicles daily consumption rises by 1,269 liters. The daily emission of CO and HC declines and NOX emission grows. In brief, u-turns have strong performance at high and medium volumes and poor performance at low volumes while it may have some negative impacts on minor street vehicles. There is high risk of collision with geometric elements of u-turns. This result is in concordance with studies that state total amount of crashes increase by 13.2 percent at u-turns.