A before-and-after study on green signal countdown device installation

This paper reports a before-and-after study which evaluated the difference in driver response along an approach of a signalized intersection installed with a green signal countdown device (GSCD). The main purpose of a GSCD is to provide drivers with a countdown timing that would help them make informed stopping/crossing decisions during the critical phase-change period. Using a special-purpose data logger, four continuous days of before-and a series of four continuous days at various months’ after-GSCD data were collected. The findings indicated that red-running violations were significantly reduced by about 65% at 1.5-month after-GSCD but its effectiveness tended to dissipate over time as the violation numbers had bounced back to almost the before-GSCD level. The dwindling effect of GSCD in curbing red-running violations in the longer term generally occurred under high traffic flows. On the other hand, the numbers of vehicles choosing to stop during the onset of amber had increased significantly by about 6.2 times at 1.5-month after-GSCD installation. The increase in red-stopping was however sustainable over the longer term, albeit a relatively small reduction was noted. The findings indicated that GSCD was practically effective in encouraging red-stopping actions under heavy traffic flows. In effect, one may conclude that the longer term performance of GSCD would only help to encourage stopping but not curbing red-violations.