Citation

Owolabi B, Noel E. ITE J. 1985; 55(2): 45-48.

Copyright

(Copyright © 1985, Institute of Transportation Engineers)

DOI

unavailable

PMID

unavailable

Abstract

This study focuses on the question of whether the user of the red arrow in lieu of red ball for exclusive right turns would result in a higher violation probability because of motorists' misinterpretation of the device. Traffic violations of the red arrow and the red ball indications were observed at 15 intersections in Washington, D.C. Overall 15,532 light cycles were observed. Important criteria for selecting the field sites were exclusive right turn signals and lanes, No-Right-Turn-On-Red (NRTOR) indicated by signing, approaches consitituting each composite site being in close proximity to each other, full utilization of signal cycles over the data collection period, and similar volume characteristics between the pair of approaches constituting each composite site. The data collection involved "before" and "after" observations. Observations at intersections with the red ball represented the "before" situation, while observations at intersections with the red arrow represented the "after" situation. The violation probability was calculated for both the red arrow and the red ball. The violation probability is defined as the ratio of the number of violated cycles to the total number of cycles with opportunities for RTOR violations. The analysis is based primarily on observed volume, cycles and violations. These parameters were used in the assemblage of the contingency tables. The Chi-square test was then used to analyze the contingency tables for testing the hypotheses; the primary hypothesis being whether the red right turn arrow will experience the same level of violation as the red ball used for the same purpose. The study concludes that the ball receives significantly fewer violations than the arrow when used for right turns, regardless of the time of day. This finding appears to support the suspicions of some practitioners that the right turn red arrow is not a safe traffic control device, and that the carryover effect of RTOR may be undermining the true potential of the right turn red arrow.