Operational Effects of U-Turns as Alternatives to Direct Left-Turns

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Abstract:

Liu, P., J. Lu, H. Zhou and G. Sokolow, “Operational Effects of U-Turns as Alternatives to Direct Left-Turns,” Journal of Transportation Engineering, Vol. 133, Issue 5 (2007)

      This study analyzed the operational effects of the right turn/U-turn maneuver as an alternative to a direct left-turn from a driveway. Data were collected at 34 selected roadway segments in central Florida. Delay and travel time were compared for various driveway left-turn alternatives under different levels of driveway volume and major road through traffic volume. The left-turn alternatives considered include direct left-turns (DLT), right-turns followed by U-turns (RTUT) at median openings, and right-turns followed by U-turns at signalized intersections. A binary logit model was developed to estimate how many drivers would like to make a RTUT instead of a DLT under different traffic and roadway geometric conditions. Specific findings were:

1.Vehicles making right-turns followed by U-turns at a downstream median opening before a signalized intersection will experience less delay as compared with those making direct left-turns at a driveway. However, when U-turns are provided at a signalized intersection, vehicles making right-turns followed by U-turns result in longer delay than those making direct left-turns at a driveway.

2.The separation distance between a driveway and the downstream U-turn location significantly impacts the running time drivers spend at a weaving section while making right-turns followed by U-turns. The running time increases with the separation distance and decreases with the major street speed limit.

3.Vehicles making right-turns followed by U-turns at a downstream median opening before a signalized intersection have comparable total travel time as compared with those making direct left-turns at a driveway.

4.The percentage of drivers selecting RTUT increases with the upstream through traffic volume, left-turn volume from major road into the driveway, and the total left-turn traffic demand at a driveway. The binary logit model developed in this study shows that more drivers prefer making RTUT at median openings rather than at signalized intersections.

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