Citation

King GF. Transp. Res. Rec. 1981; 811: 7-14.

Copyright

(Copyright © 1981, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

An empirical determination of traffic signal visibility is presented. The study used subjects seated in stationary vehicles viewing standard, full-sized traffic-control signals at distances ranging from 370 to 1300 ft. Data, including response accuracy and response latency, were collected for both day and night ambient lighting conditions. It was found that currently used circular traffic-signal indications are generally adequate for nighttime service but their adequacy for daytime conditions is suspect. Signal visibility was found to be somewhat insensitive to signal lens size and illumination intensity for nighttime operations, which implies that even the dimmest signal tested (8-in lens with 67-W bulb) is above threshold visibility for all distances at night. The single most important factor affecting the visibility of traffic signals during the day is signal color. Green indications generally led to the poorest subject response, in terms of both response accuracy and response time, for the daytime observations. In relation to visibility considerations alone, the data obtained present strong support for the possibility of dimming all colors of 12-in signal indications at night.