Impact of Countdown ground LED lights on traffic flow efficiency at signalized intersections: a driving simulator study

Abstract

Unnecessary stopping at signalized intersections during yellow interval reduces traffic flow efficiency. The aim of this driving simulator study was to investigate the impact of an advanced countdown system on traffic flow efficiency during yellow interval at signalized intersections. The experiment was conducted using a driving simulator at Qatar Transportation and Traffic Safety Centre, Qatar University. Sixty-seven volunteers with a valid Qatari driving license participated in the study. Three signalized intersections for three scenarios were designed with the north bound of the Corniche road in the city of Doha as the real-life reference context. The control scenario was an untreated typical signalized intersection (default) with the signal order of green-yellow-red. The signal order was changed to green-flashing green-yellow-red in the condition with 3 seconds advanced flashing. In the third scenario, green LED lights were used as an advanced countdown system and was compared with a default traffic signal with order green-yellow-red and a flashing green traffic signal with order green-flashing green-yellow-red. The LED lights were installed over a 100 m stretch of the road surface with spacing of 5m. More specifically, these ground lights were integrated in the pavement marking strips indicating lane division and edge lines. Light units were flashed green, 3 seconds prior to the yellow interval, and then turned off one by one in sequential order towards the intersection at a predetermined speed. The system was aimed at providing advanced information and visualizing the inter-green period by means of a countdown system as a way to improve traffic flow efficiency. Study results showed that compared to the other two scenarios, drivers' utilized the yellow interval in a better way in the scenario with green LED lights. Furthermore, results from binary logistic regression showed that probability of crossing the intersection was 30 and 2.6 times higher in the scenario with green LED lights compared to the flashing green and control scenarios, respectively. Regarding the red light running occurrences, there was no significant differences between the scenarios. Taking into account the results from this study, we recommend jurisdictions to further evaluate G-LED as a potentially effective treatment for increasing traffic flow efficiency during the inter-green period at signalized intersections.