Study Found In-Vehicle Signal Countdown Timer Reduced Mean Speed by 15 Percent and Increased Deceleration by Three Times During Yellow or Red Phases, Indicating Improved Driver Awareness and Safety at Intersections.
Providing Real-Time Traffic Signal Phase Information to Drivers in a Virginia Study Helped Moderate Drivers’ Speed and Deceleration.
Merrifield
Investigation of Key Automated Vehicle Human Factors Safety Issues Related to Infrastructure: Comparing Intersection Crossing Behaviors of Human Drivers and Automated Vehicles
Summary Information
Traffic signals at intersections control vehicle movements and guide driver behavior. When approaching a signalized intersection, drivers must determine whether they can proceed (green signal phase) or stop (red signal phase). The decision to proceed or stop during a yellow signal phase has important safety consequences, and additional information, such as an in-vehicle signal countdown timer, has the potential to increase intersection safety. The objectives of this study were to examine the degree to which an in-vehicle signal countdown timer influenced human drivers’ intersection approaching behaviors and decision making.
METHODOLOGY
The study was conducted at the intersection of a 1.5-mile route of Lee Highway and Eskridge Road and Merrilee Drive in Merrifield, VA and analyzed observed human driver data from 57 participants from May and June 2023. Participants drove instrumented vehicles with a display screen showing signal phase countdown information. The in-vehicle display remained blank for the control group. Data collected included vehicle measurements (speed and acceleration of the test vehicle), eye-tracking data recorded by a camera in the test vehicle, and responses to a post-drive questionnaire. The researchers also collected 30 days of data from an automated electric shuttle between August and November 2021. The research team noted limitations such as naturalistic setup, which resulted in the collection of an uneven number of signal phase change sequences.
FINDINGS
The presence of the signal countdown timer information appeared to have regulated drivers’ speed and acceleration within the approach zone.
- When the signal phase was yellow or red in the beginning of the approach, the countdown group had approximately 15 percent lower speeds than the control group (21.5 mph versus 25.5 mph). The countdown group also decelerated by 316 percent more (-0.258 m/s2 versus -0.062 m/s2).
- When the signal phase remained green during the approach, the countdown group decreased speed less than the control group (-0.461 mean of speed difference compared to -4.830 mph).
- When the signal phase changed from red to green while the test vehicle was stopped, the countdown group accelerated more than the control group (1.42 m/s2 versus 0.99 m/s2).
