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5 CHAPTER ONE INTRODUCTION The findings presented in the study were based on a literature could be addressed through the development of several timing review [conducted to gather as much information as possible plans covering various traffic-demand scenarios and a good about Adaptive Traffic Control Systems (ATCS) operations selection process triggering replacement of these timing plans. and deployments from previous studies] and two electronic However, several experiments around the globe, of which the surveys: a shorter e-mail survey for vendors or developers of most prominent was done by the FHWA in Washington, D.C., 10 major ATCSs and a website-based questionnaire for agen- showed that traffic-responsive pattern-matching systems cies that deploy ATCSs. The survey was originally distributed have serious operational problems (Fehon 2005). The experi- to 42 agencies that run ATCSs in North America (United ments showed that traffic control based on traffic-responsive States and Canada) and several dozen locations around the pattern selection is not efficient. By the time one pattern transi- world. Numerous follow-up requests were made, by e-mail tions to another, traffic demand may change and the newly and telephone, to remind agencies that had not yet responded introduced pattern may no longer reflect current traffic condi- asking them to participate. Responses were obtained from tions. Furthermore, transitions themselves may represent a dis- 34 of the 42 agencies in North America using an ATCS, an ruption to traffic. The increasing frequency of pattern changes 81% response rate. Also, 11 responses were received from may improve matching between signal timings and traffic con- agencies in other countries. Of the North American agencies, ditions, but the system may spend most of the time in transi- 42% were municipal entities, 20% were counties, 13% were tioning, which may cause a continuous disruption to traffic. state agencies, and 25% were other types of entities. This chap- ter will define and introduce ATCSs. A short history of ATCSs To solve this problem, traffic engineers in Australia and the and their classifications will be provided. Major ATCSs in United Kingdom responded by investigating adaptive control use throughout the world will be identified along with the of signal timings, which resulted in the development of the agencies that operate these systems. two most widely used ATCSs: the Sydney Coordinated Adap- tive Traffic System (SCATS) (Lowrie 1982) and the Split Cycle Offset Optimization Technique (SCOOT) (Hunt et al. BACKGROUND 1981). Development of these systems was quickly followed by a series of other new ATCSs. However, some of these new An ATCS adjusts, in real time, signal timing plans based on ATCSs abandoned conventional signal timing structures con- the current traffic conditions, demand, and system capacity. strained by cycle lengths and offsets and, instead, offered new An ATCS is defined broadly, in the previous sentence, so approaches that were mostly based on various techniques of as to include all major ATCSs that may vary significantly in mathematical programming: OPAC (Optimization Policies for their levels of responsiveness, algorithmic framework, and Adaptive Control) (Gartner 1982) and PRODYN (Program- detection. However, ATCSs, as defined in this report, exclude ming Dynamic) (Henry 1983). At that time, OPAC, PRODYN, any traffic-responsive pattern selection and purely actuated and SPOT (System for Priority and Optimisation of Traffic) (free or coordinated) types of traffic control. An ATCS usually (Donati et al. 1984) were largely concerned with the opera- includes algorithms that adjust a signal's split, offset, phase tions of single intersections. Soon thereafter, UTOPIA (Urban length, and phase sequences to minimize delays and reduce Traffic Optimisation by Integrated Automation) was com- the number of stops. The system requires extensive surveil- bined with SPOT to account to changes at the network level lance, historically in the form of pavement loop detectors, (Mauro and DiTaranto 1990). and a communications infrastructure that allows for commu- nication with the central and/or local controllers. Although most of these developments were taking place in Europe, at approximately the same time the FHWA initialized Emergence of ATCSs during the 1970s and early 1980s was development and deployment of ATCSs in the United States. largely attributable to a failure of traffic-responsive pattern- The Adaptive Control Software (ACS) program included a selection systems to efficiently respond to changes in traf- research project called Real-Time Traffic-Adaptive Signal fic demand. In the early 1970s, there were a few attempts to Control Systems (RT-TRACS) that had gone through several develop ATCSs; however, there was no success with these stages to the point where there were several adaptive systems early trials (Holroyd and Hillier 1971). At that time, traffic sig- on trial in U.S. cities (Fehon 2005). Although the program nal practitioners believed that fluctuations in traffic flows initially sponsored development of five prototype strategies,