Knowledge Resources

In April 2008, the Orange County Transportation Authority (OCTA) began implementation of the inter-jurisdictional, multi-phase Traffic Light Synchronization Program (TLSP) along the county's 10 major corridors, including the Alicia Parkway corridor. The Alicia Parkway corridor spans 11 miles (17.7 kms) and includes 41 signalized intersections; it also travels across five cities (Aliso Viejo, Laguna Hills, Laguna Niguel, Mission Viejo and Rancho Santa Margarita). The project was complicated by the fact that it required coordination among multiple agencies from the five cities spanned by the corridor.

The TLSP aimed to reduce the number of stops on the corridor, thereby improving mobility. Implementation included upgrades to traffic management systems, intersection traffic signal controllers, communication systems, and new optimized signal timing. The synchronization system, which is typically activated during the morning and evening peak traffic hours, uses timers that are set to congestion levels to turn traffic lights green.

METHODOLOGY

To determine the impact of synchronizing traffic lights on the Alicia corridor, before and after studies used data obtained from traffic in the westbound and eastbound directions in the morning, midday, and evening periods. The studies compared travel times (in minutes), the number of stops, average speed, and greenhouse gas production across the different conditions.

FINDINGS

The implementation produced a system that used timers set to current traffic patterns and congestion levels to turn traffic lights green, resulting in a reduction in travel delay and lower vehicle emissions. Specifically, the project produced the following benefits:

• Average commute speed increased by as much as 31 percent.
• An overall reduction of up to 75 percent in the number of stops.
• An 11 percent reduction in travel times.
• A savings of 1.1 million gallons of fuel over three years.
• A reduction of 7 percent reduction in greenhouse gas emissions.

The studies did not find improvements in all locations in the corridor. For example, the Laguna Niguel, Aliso Viejo and Laguna Hills city segments did not have an improvement in travel time nor the number of stops in the morning and evening commuting periods. The authors attribute this finding to the fact that these cities had previously upgraded their traffic light synchronization.

The findings suggest that inter-jurisdictional cooperation in signal synchronization projects will produce greater benefits compared to when jurisdictions act independently from one another.