Traffic Light Displays and Driver Behaviors: A Case Study

Abstract

This research examined driver behavior towards four types of traffic light warning schemes currently in use across Metro Manila, Philippines. The first phase of the study involved surveys with drivers to know what they say they do upon reaching the red, yellow, and green lights at intersections. These were used to establish expected norms for driver behavior. The surveys showed that 99.5% of drivers claimed they stop at red lights, 76.3% slow down at yellow lights, and 98.2% either speed up or maintain speed at green lights. These results were then compared to the second phase of the study which involved observing actual driver behaviors through independently recorded video footages of intersections with different types of traffic lights: blinking lights, lights with countdown timers, and lights without warning schemes. Actual behavior differed from claimed behavior: instances of crossing of red lights were 7.0% higher than expected, slowing down was the least preferred behavior at yellow lights, and the preference at a green light was to maintain speed but that slowing down and speeding up were also exhibited. ANOVA analyses showed that countdown timers significantly decreased ‘startup’ times and increased the proportion of cars that sped up at yellow lights. Additionally, it was determined that countdown timers create a sense of urgency for drivers in the last 5seconds —as do blinking lights during the blinking phase — increasing the tendency to speed up in both types of lights’ warning phases. None of the warning schemes, however, affected red light behavior. Through the third phase, where the researchers observed case subjects who drove a pre-designated route designed to go through lights with countdown timers and without warning schemes, it was determined that yellow light behavior is primarily a function of distance and speed, while green light behavior is more a function of certainty regarding the time left to cross. Hence, countdown timers were determined to be the most efficient, and primarily for this reason, were recommended, especially as they seemed to add little to no additional risk at red and green lights. Finally, it was seen that factors like traffic, road situation, light design, light intensity, blocks, etc., play a key role in traffic light behavior, and should thus be further investigated.