The estimated benefit-to-cost ratio for optimizing signal timing plans, coordinating traffic signal control, and implementing adaptive signal control in California was 17:1.

7-11 January 2001
Statewide,California,United States

Summary Information

This paper summarizes an evaluation of the benefits of optimizing traffic signal timing plans, coordinating traffic signal control, and implementing adaptive signal control at locations throughout the State of California. The signal timing optimization and coordination projects were carried out during the Fuel Efficient Traffic Signal Management (FETSIM) Program, between 1983 and 1993. This program involved 163 local agencies and 334 projects, improving 12,245 signals at a cost of $16.1 million, or $1,091 per signal. Timing plans were developed using the TRANSYT-7F software package. TRANSYT-7F also produced estimates of delay, number of stops and fuel consumption under the recommended signal timing plans, indicating the benefits of optimization. This created a database of the impacts of coordinated signal timing optimization under a variety of local conditions across the many projects implemented during the FETSIM program. Data from the Los Angeles Advanced Traffic Control and Surveillance System (ATSAC), allows an assessment of the performance of traffic responsive signal control at several intersections. The results presented in this paper are based on analysis of the accumulated statistics from the local agencies carrying out the signal improvement projects.

The TRANSYT-7F model estimates from 163 of the 334 FETSIM projects (49 percent), representing 55 percent of the total number of signals retimed, demonstrated positive results from signal retiming of coordinated signal systems. The study found an average 7.7 percent reduction in travel time, 13.8 percent reduction in delays, 12.5 percent reduction in stops and 7.8 percent decline in fuel use. This study excluded TRANSYT-7F results for oversaturated approaches, as the simulation overestimates the benefits of retiming under these conditions. Results of "before" and "after" floating car studies reported by some of the jurisdictions support the TRANSYT-7F figures. The average reductions reported by the floating car studies were: 7.4 percent in travel time, 16.5 percent in delay, and 17 percent in stops. The differences between these figures and the TRANSYT-7F values are due to the survey routes selected by the projects, which did not cover each link of the retimed signal network.

There was considerable variation in the improvement achieved by the retiming projects, for a variety of reasons:
  • Quality of existing timing plans: When existing timing plans were already performing well, there was often little benefit in signal optimization.
  • Network configuration: The largest savings were obtained on arterials, rather than signalized grid networks.
  • Traffic Patterns: High volume systems with predominant through movements achieved the greatest improvements. Savings were marginal on systems containing several congested intersections in need of capacity improvements.
  • Signal Equipment: Systems with actuated signals and easily modifiable control parameters achieved greater benefits.
"Before" and "after" field studies using floating cars assessed the performance of 76 of the projects that implemented coordinated signal control during the FETSIM program. The report indicted the benefit-to-cost ratio for the cumulative impact of all the FETSIM projects, as determined by the recommended AASHTO method, was 17:1.

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ITS Benefits: The Case of Traffic Signal Control Systems

Author: Skabardonis, Alexander

Published By: Paper presented at the 80th Annual Transportation Research Board Meeting. Washington, District of Clolumbia

Source Date: 7-11 January 2001


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Goal Areas


Typical Deployment Locations

Metropolitan Areas


traffic signals, adaptive signals, coordinated signals, signal coordination, centralized signal control, signal synchronization, advanced signal control, signal timing optimization, coordinated signal control, advanced signal controller, traffic signal retiming, retiming, Coordinated signal timing, pre-timed, pretimed, time-of-day signal timing, fixed-time

Benefit ID: 2001-00176