Simulation and Field Data Analyses Used to Assess Integrated Intelligent Intersection Control System Before and After Deployment at a Prince George’s County Intersection.
Maryland, United States
An Integrated Intelligent Intersection Control System (III-CS) for Safety Improvement and Delay Minimization
Summary Information
Building on the intersection dilemma zone protection system (DZPS) previously developed in Maryland, researchers developed and tested a more advanced system known as the Integrated Intelligent Intersection Control System (III-CS). While the DZPS used a long-range sensor to detect approaching vehicles’ speeds and locations, drivers sometimes did not take reactive actions such as reducing speed, especially during the yellow interval. The key features of the III-CS included optimizing the green termination algorithm to minimize the likelihood of rear-end collisions and total traffic delay, and activating an all-red extension when red-light running vehicles are detected. After assessing characteristics of three candidate intersections, III-CS was deployed at one intersection on Maryland State Route 4 in Prince George’s County. Field data was collected on two days in January and March 2021, approximately one and three months after full deployment, and compared with pre-deployment data from a day in April 2019.
Methodology
Using field data to calibrate key parameters, researchers executed simulation analyses to evaluate the pre-deployment conditions and estimate the risk of rear-end and angle crashes. To estimate potential benefits of the III-CS green termination algorithm and all-red extension, a comparison of the intersection’s traffic speeds, volumes, vehicles trapped in dilemma zone, and red-light running vehicles was conducted for the before and after deployment conditions. Mobility impacts were assessed using measurements of speed and volume which can be associated with travel time and traffic congestion.
Findings
- The average hourly number of vehicles in the dilemma zone, which is a direct contributor to an intersection’s collision risk, was lower after III-CS deployment by approximately 18 percent. In the pre-deployment condition, this measure was 48.3 vehicles per hour (vph) while post-deployment measures were 39.7 and 39.4 vph.
- The Type-II dilemma zone, which is based on drivers’ decisions to pass through or stop at the intersection upon seeing the yellow indication, was slightly narrower after the system deployment, likely due to improved transition timing from green to yellow. Before deployment the range of time-to-stop-line was 2.2-6.7 seconds, while post-deployment range observations were 1.7-6.2 seconds and 2.1-6.2 seconds.
- The reduction in the deceleration-related statistics indicated that after deployment of III-CS, drivers behaved less aggressively over time. For example, in the observation three months after deployment, the maximum, 85th percentile, and average deceleration rate of vehicles approaching the intersection during the yellow interval were reduced from 15.4 to 11.0 ft/s2, 7.96 to 5.73 ft/s2, and 3.28 to 2.15 ft/s2, respectively. Speed distribution patterns after deployment were also observed to be slower and smoother.
- The average number of red-light running vehicles per cycle decreased from 0.119 before deployment to 0.063 and 0.116 in the two after-deployment periods. However, researchers noted a need to conduct more field assessments with longer durations.
