Safety Evaluation of Right Turns Followed by U-Turns as an Alternative to Direct Left Turns - Conflict Analysis

This project evaluated the safety and operational impacts of two alternative left-turn treatments from driveways/side streets. The two treatments were (I) direct left turns and (2) right turns followed by U-tums. Safety analyses of the alternatives were conducted using two major approaches: traffic crash data analysis and conflict analysis. Findings related to the traffic conflict analysis are documented in this report. Two other reports document the crash data and operational analyses. Ten sites were selected for field data collection where each site experienced one or both of the left tum alternatives from the driveway or side street. Video cameras were set up on scaffoldings to achieve enough viewing height and all the traffic movements at the selected sites were recorded. These videotapes were later reviewed and conflict data related to direct left turns or right turns followed by U-turn movements were gathered, together with corresponding traffic volumes and conflict severities. Nine different conflict types related to the left tum movements were considered. The average number of conflicts and conflicts per thousand involved vehicles were estimated using the collected data. The average number of hourly conflicts for direct left turns was 6.35, whereas the corresponding value for right rums U-turns was 4.2. When the results were separated by time period, the differences were more significant during peak periods. The average number of conflicts per thousand involved vehicles for direct left turns and right turns followed by U-turns were 30.2 and 18.7 respectively. A before and after comparison was also conducted at a site that underwent a median closure thereby allowing only right turns followed by U-turns. Results showed that the total average number of conflicts per hour was reduced by almost 50% by replacing direct left turns with right turns followed by U-turns. Conflict severity for the after period was also significantly lower than that for the before period. Several different approaches to evaluating traffic conflicts resulted in the conclusion that the right turns followed by U-turn movement was safer than that of direct left tum movement