Title

DRIVER UNDERSTANDING OF SIMULTANEOUS TRAFFIC SIGNAL INDICATIONS IN PROTECTED LEFT TURNS

Document Type

Journal Article

Publication Date

2002

Subject Area

operations - traffic, infrastructure - vehicle, infrastructure - traffic signals, planning - surveys, ridership - drivers

Keywords

Traffic signals, Traffic signal indications, Traffic lights, Traffic control signals, Surveys, Signal displays, Protected permitted left turns, Motor vehicle operators, Highway traffic signals, Elderly drivers, Drivers, Driver errors, Comprehension, Aged drivers

Abstract

A comprehensive assessment of protected and permitted left-turn (PPLT) signal displays was performed considering safety, operational performance, and driver-understanding measures. The research focused on a study of driver understanding of protected left-turn indications. All currently used PPLT display arrangements and protected indication combinations were evaluated, including those with simultaneous green-arrow and red- or green-ball indications and those with the green-arrow indication only. Driver understanding was evaluated through a computer-based driver survey completed by 2,465 drivers. In total, 73,950 survey responses were received pertaining to the 200 different survey scenarios evaluated, 24,863 pertaining to protected left-turn indications. Findings show that the simultaneous illumination of the green-arrow and red-ball indications in a five-section PPLT signal display during a protected left-turn phase significantly reduces driver understanding and increases driver error. This finding is especially true for drivers over the age of 65. Simultaneous illumination of the green-arrow and green-ball indications also resulted in levels of driver understanding lower than the green-arrow-only indication; however, these differences were not statistically significant.