Good Practice Traffic Signal Timing - ACS-Lite

Adaptive Control Software Lite (ACS-Lite) is a low cost signal timing optimization system the dynamically adjusts signal timing to meet current traffic demands. Traditional traffic signal timing is designed by sampling traffic demand during peak periods and designing signal timing to meet those demands. Most agencies do not commit sufficient resources to evaluate and retime traffic signals on the recommended frequency of 3 to 5 years. As communities grow and traffic demands change due to schools opening and closing, seasonal shifts, special events and a host of other sources, congestion and delays are frequently the result. ACS-Lite is a technology solution that allows signal timing to address changes in demand and adjust signal timing appropriately.

As part of ACS-Lite testing, researchers conducted a before-and-after traffic study on State Route 70 in Manatee County, FL, to assess the benefits of the software. Specifically, the study focused on collecting data on traffic volumes at eight intersections between Caruso Road to the east and U.S. 301 to the west, performing "floating car" travel time and delay studies, and conducting statistical analyses on traffic volume, speed and travel time, and delay data. The floating car methodology involves performing travel time runs using a test vehicle driven at an average speed through the arterial, allowing vehicular speed to be dictated by the platoon speed, not the posted speed limits. Travel time measurements begin when the test vehicle passes the stop line at the first intersection and end when the vehicle passes the stop line at the last intersection in the section or arterial being evaluated.

The result indicated that the total travel time, stopped delay, number of stops, and fuel consumption decreased during the "after" study period when the ACS-Lite software was in effect. In addition to a 9 percent reduction in network traffic volumes between the "before" and "after" study periods, the researchers also reported a 12 percent reduction in travel time, 28 percent reduction in travel time delay, attributing a significant portion of the gains to the ACS-Lite software.

ACS-Lite was developed through a public private partnership between FHWA, Siemens, The University of Arizona, Purdue University, Siemens/Eagle, Econolite, Quixote/Peek and McCain Traffic. Field test of ACS-Lite have resulted in estimated annual user costs savings ranging between $88,000 and $757,000.