Graduation Year


Document Type




Degree Granting Department

Civil Engineering

Major Professor

Jian John Lu, Ph.D.


Traffic safety, Traffic conflicts, Direct left turn, Access management, Separation distance


The objective of this study was to determine the safety impacts of right turn followed by U-turn movements (RTUT) at signalized intersections as well as median openings. RTUT movements are the most common alternatives to direct DLT movements(DLT). In order to achieve such data in a shorter amount of time, conflict analysis was chosen to be useful in this study as opposed to crash analysis. Additionally, data collection sites were divided dependent on certain geometric criterion and conflict data was recorded by the use of video recording equipment. Seven out the eleven conflict types used during the study were related to RTUT movements while the remaining observed conflicts were related to DLT movements. The safety comparison of right turns followed by U-turns to direct left turns at traffic signal sites indicated that DLT movements generated two times more conflicts per hour than RTUT movements.

When the effects of traffic volumes have been taken into consideration, RTUT movements had a 5 percent higher conflict rate than DLT movements. At median opening sites, DLT movements generated 10 percent more conflicts per hour than RTUT movements. Furthermore, the other conflict rate, which takes the effect of traffic volumes into consideration, was 62 percent higher for DLT movements as compared to RTUT movements.Impacts of separation distance on safety of RTUT movements were investigated by a regression model. The model investigated impacts of U-turn bay locations and the number of lanes on major arterial on separation distance requirements. The model results indicated that U-turn bays located at signalized intersections and greater number of lanes on major arterials increases the minimum separation distance requirements. Finally, on four lane arterials U-turn distributions at median openings were analyzed to investigate how U-turns are accommodated at such locations.

A u-turn regression model was developed to investigate impacts of median modifications on signalized intersection safety. The model results indicated that median modifications across the high volume driveways may cause safety problems at downstream signalized intersection.