Evaluation of Methods for Left-Turn Gap Analysis Using High-Resolution Signal Data

Abstract

This project evaluates the most underutilized but potentially the most useful automated traffic signal performance measure (ATSPM) tool in decision-making for left-turn phasing at signalized intersections. Lack of data quality control or quality checks and a difficulty in using the currently presented measure on the website have been identified as shortcomings of the “left-turn gap analysis” measure. The purpose of this project is to develop an automated method of flagging intersection approaches in need of left-turn phasing changes based on availability of gaps in opposing through traffic. Through comparison with manually collected data, high-resolution data from selected approaches were validated. The validated sample data were then used to develop a gap analysis tool which, in conjunction with identified automated measures, can identify and flag left-turn locations requiring phasing changes (adjusting between permissive-only, protected-permissive, and protected-only). The tool is currently being migrated to the Utah Department of Transportation ATSPM website to be made available to engineers and consultants in the form of a password-protected online measure.