This paper provided an overview of commonly deployed adaptive traffic signal control systems. A literature review was conducted to detail functions and features of the five most widely deployed systems in the United States and other countries. The table below provides a brief description of each type of control system.
|System||Year (Place Developed)||
Features and Methodologies
Number of Deployments
(Split Cycle and Offset Optimization Technique)
|1970 (UK)||Optimizes Splits, Cycle and Offsets; real-time optimization of signal timing||More than 200 locations worldwide; around 10 locations in the USA.|
(Sydney Coordinated Adaptive Traffic System)
|1970 (Australia)||Optimizes Splits, Cycle and Offsets; selects from a library of stored signal timing plans||More than 50 locations worldwide; more than 10 locations in the USA.|
(Optimization Policies for Adaptive Control)
|1990 (USA)||The network is divided into independent sub-networks||4 locations in the USA.|
(Real Time Hierarchical Optimized Distributed Effective System)
|1990 (USA)||Mainly for diamond interchange locations||4 locations in the USA.|
|ACS Lite||1990 to 2006 (USA)||Operates with predetermined coordinated timing plans; automatically adjust splits and offsets accordingly||3 locations in the USA.|
SCOOT has the largest world-wide deployment with SCATS the largest in the United States. The number of OPAC and RHODES deployments was limited. Although the number of ACS Lite systems deployed was relatively small due to its short history, the number of these systems is expected to grow as a result of its low cost and compatibility with existing closed-loop systems.
According to the literature review, adaptive systems provide significant benefits over traditional time-of-day coordination plans. The improvements are based on reduced stops, delays, and fuel consumption.
The table below summarize results from field studies.
|Adaptive Signal Control System|
|SCOOT||-29% to -5%||-28% to -2%||-32% to -17%|
|SCATS||-20% to 0%||-19% to 3%||-24% to 5%|
|OPAC||-26% to 10%||-55% to 0%|
|RHODES||-7% to 4%||-19% to -2%|
|ACS Lite||-12% to 7%||-38% to 2%||-35% to -28%|