Research on the Impact of U-turn Location on Operation Efficiency at Intersection

Direct left turn (DLT) at intersection has a lot of safety and operation problems. For example, it increases traffic conflicts, delay and reduces capacity of the road network. Increasingly, Right turn plus U-turn or U-turn plus right turn (RT+UT or UT+RT) at intersection as an alternative to DLT has been considered as an important access management. Many states and transportation agencies are considering to applying the access management. However, some operation problems emerge in practical application. For example, U-turn location selection is ill-defined, experiential and short of systemic programming theory. The impact of the treatment and applicability is still not very clear in China for the different traffic conditions with overseas countries. The primary objective of the study is to examine the influence of U-turn location selection to the effectiveness of U-turn at signalized intersections under the different conditions of traffic volume and percentage left turns. And set up a set of guidelines for using this alternative in China. To achieve the objectives, firstly, the traffic character under different U-turn location is analyzed. Secondly, delay and travel time models of U-turn are proposed. Then, the microscopic traffic simulation software VISSIM is used to make simulation of the different conventional location of U-turn traffic managements under different traffic volume and percentage left turns at intersection. For the precision of simulations, the simulation parameters are calibrated by using the field observed data. The average delay is used as performance estimation parameter. The trend lines of the relationship between average delay and different traffic volume on arterials and percentage left turns was developed. Consequently, the findings of this study are helpful in providing local and state transportation agencies with recommendations for the selection of access managements and various driveway left-turn alternatives on multilane roadways.