AN ANALYTICAL-HIERARCHY-PROCESS APPROACH TO DETERMINE LEFTTURN CONTROL TYPES AT SIGNALIZED INTERSECTIONS

摘要

There are three left-turn control types generally used at signalized intersections:permitted (PM), protected/permitted (PP), and protected only (PT). Many studies havedeveloped warrants and guidelines for selecting left-turn control types, and most guidelines areusually presented in a flow chart format according to selected variables such as number of leftturnlanes, traffic volumes of left-turn and opposing through movements, number of left-turnand opposing lanes, speed limit of opposing traffic, sight distance, and number of crashesrelated to left-turns. One of the major drawbacks of these guidelines is that a left-turn controltype can be decided based on one dominant factor, lacking a balanced consideration of all theaforementioned factors. This paper introduces a new approach based on the AnalyticalHierarchy Process to determine left-turn control types. Instead of going through a flow charttype selection, a ranking score considering all these factors is produced to represent thelikelihood of using a certain type of control. Furthermore, the proposed approach can be easilyadapted to suit aggressive, moderate, or conservative decision makers. Finally, the proposedapproach was applied to a case study that involved implementation of flashing-yellow-arrowprotected-permitted display at 14 intersections in the Reno-Sparks area in Nevada.