Citation

Hadi MA, Thakkar J. Transp. Res. Rec. 2003; 1847: 58-65.

Copyright

(Copyright © 2003, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Limited research is available to help transportation agencies make decisions about installing right-turn deceleration lanes at uncontrolled approaches of unsignalized intersections and driveways. Criteria for right-turn lanes developed by some agencies do not adequately consider the effects of through and right-turn movement volumes and speeds. To evaluate the need for right-turn lanes, the percentage of through vehicles behind right-turning vehicles in the outside (right) lane that perform evasive maneuvers because of the presence of right-turning vehicles has been used as a surrogate. This measure is difficult to use under different combinations of volumes, speeds, and other operating conditions; it also cannot be estimated from traffic simulation models if these models are used to evaluate the need for right-turn deceleration lanes. Safety is the most important factor when deciding to provide a deceleration right lane. The speed differential between through vehicles affected by right-turning vehicles and those not affected by these turns is used to determine the need for right-turn deceleration lanes at unsignalized intersections. The speed differential measure has been shown to be a surrogate to safety and to be related to crash involvement. To determine the total speed differential caused by right-turning vehicles in the outside lane, two variables are needed: the number of through vehicles in the outside lane affected by right-turning vehicles and the average drop in speed of affected vehicles. Total speed differential can be used to evaluate the need for a right-turn deceleration lane.