Graduation Year

2004

Document Type

Thesis

Degree

M.S.C.E.

Degree Granting Department

Civil Engineering

Major Professor

Jian John Lu.

Keywords

DLT, delay, travel time, RTUT

Abstract

Direct left turn (DLT) movements have a lot safety and operation problems. They increase conflicts, delay and reduce capacity of the roadway. Increasing, many states and transportation agencies are considering using right-turns followed by u-turns as an alternative to direct left turns. Recently, Florida state are planning to close median openings in order to reduce the safety and operational problems caused by DLT. The left-turn egress movement would then to be made by turning right to the arterial road and then making a u-turn at an available downstream median opening or a signalized intersection.

FDOT sponsored a project in 2001 (Methodology to quantify the Effects of Access Management Treatments on Roadway Operations and Safety) which has provided useful information on operational effect of right-turn followed by u-turn at median opening as an alternative to the direct left turn from driveways. However, the impact of the treatment---right-turn followed by u-turn at signalized intersection as an alternative to direct left turn is still not clear. A operational comparison of this treatment would be valuable. Field data collection was conducted to quantify the operational effects of right turn followed by u-turn at signalized intersection versus direct left turns. Totally eight sites around the Tampa Bay area were selected and more than 300 hours field data including delay, travel time, traffic volume, traffic control, headway, signal timing and geometric data were collected.

Data reduction was conducted after that and several statistic models were developed evaluating total travel time, travel delay of these two movements and the ratio of drivers choice of RTUT versus DLT. As the conclusion, the study found that RTUT followed by U-turn at signalized intersection has longer delay and longer travel time as compared to DLT and the existence of long cycle downstream signal will discourage driver's selection of RTUT. There conclusions are very important in that they provided decision makers with useful information regarding the selection of the suitable U-turn location.

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