Safety Evaluation of Direct Left Turns Vs Right Turns Followed by U-Turns Using Traffic Conflict Technique

Abstract

This paper describes a safety evaluation of two left-turn alternatives: direct left turns (DLT) and right turns followed by U-turns (RTUT), from driveways using traffic conflicts analysis. Seven sites were selected for field data collection where each site experienced one or both of the left turn alternatives. Video cameras were set up on scaffoldings to achieve enough viewing heights and all traffic movements at the selected sites were recorded. These videotapes were later reviewed and conflict data related to DLT or RTUT movements were gathered, together with corresponding traffic volumes and conflict severities. Nine different conflict types related to the left turn 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 DLT was 6.34, whereas the corresponding value for RTUT was 4.18. Differences in hourly conflict rates were more significant during the peak periods where the rates were 7.01 and 3.98 respectively for DLT and RTUT. When average number of conflicts per thousand involved vehicles was considered, the rates for DLT and RTUT were 26.43 and 16.08 respectively. RTUT conflict rate was 39% lower as compared to DLT conflict rate. Severity of conflicts for DLT and RTUT was also analyzed by using two approaches based on Risk of Collision and Time to Collision scores. In both cases, DLT conflict severities were significantly larger than that of RTUT. The results from all means using traffic conflicts indicated that the safety situation of RTUT as much better than that of DLT.