A Real-Time AI-Assisted Traffic Signal Control System in San Anselmo, California, Reduced Time Spent in Traffic by Approximately 30 Percent at a Cost of 30 Cents Per Hour to the City.
Field Deployment at One Busy Intersection Evaluated Changes in Time Spent in Traffic Following Implementation of the AI-Assisted Signal Controller.
San Anselmo
San Anselmo using AI-controlled traffic lights at busy intersection
Summary Information
Congestion and delay at busy signalized intersections can result in excessive waiting at red lights and reduced overall intersection efficiency. A live traffic signal control system that uses an artificial intelligence (AI)-based controller to manage signal operations in real time was piloted at the busiest intersection in Marin County, California, known as "The Hub," where Sir Francis Drake, Red Hill and Center Boulevards meet in San Anselmo. The controllers continuously detect and track cars, bicycles, buses, and pedestrians moving around the intersection and map them in a three-dimensional space. The AI-based controller was deployed in August 2025.
METHODOLOGY
Based on the positions and velocities of vehicles and road users, the system ran real-time traffic simulations up to 10 times per second and selected the most effective signal timing from allowable signal plans, optimizing for throughput or safety. The changes observed in time spent at this intersection were used to assess the system’s performance.
FINDINGS
- The system reduced time spent in traffic at The Hub by about 30 percent, saving drivers a combined 91 hours, at an estimated cost of 30 cents per hour to the city.
