F. Pirinccioglu, J.J. Lu, J.C. Pernia
Direct left turns (DLT) from the driveways have been a concern for transportation engineers as a major source of operational and safety problems. In the past, several studies have been conducted addressing the safety and operational problems related to DLT movements, and alternatives to direct left turn from driveways. This paper evaluated the safety effects of right turns followed by U-turns at signalized intersections (RTUT) as an alternative to direct left turns from driveways and side streets. The safety evaluation was accomplished by comparison of traffic conflicts. Nine types of conflicts were selected for this study. Five of the conflicts were related to RTUT movements, while the rest of them were related to DLT movements. Data were collected with the help of video recording equipment at a total of eight sites for over 300 hours. Two types of conflict rates, conflicts per hour and conflicts per thousand involved vehicles were used for safety comparison of the two left turning alternatives. DLT movements generated averagely 6.7 conflicts per hour, while RTUT movements generated 2.4 conflicts per hour. On the other hand, average number of conflicts per thousand vehicles involved for DLT and RTUT movements were 40.6 and 26.2 respectively. Severity of conflicts was analyzed by use of Risk of Collision (ROC) scores. In general, when both DLT and RTUT are compared, based on the results of this study, RTUT movements reduce the number of conflicts, and the overall severity of RTUT related conflicts are significantly lower than that of DLT related conflicts.
Keywords: safety evaluation; signalized intersection; U-turn; conflicts; severity analysis