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7 STUDY METHODOLOGY outlook of such systems. Analyzing these documents provided insight into ATCSs, created sound knowledge of existing The study methodology consisted of three tasks. The first implementation issues, and established a platform for evalu- focused on the selection of ATCSs, which are typically ation of the survey data. The study itself does not refer to all deployed in the United States (and worldwide) and iden- of the documents gathered through the literature review. For tification of ATCS agencies that need to be interviewed. the purposes of future research on ATCS, they are categorized The second task was to conduct a literature review and and cited in Appendix C. gather as much information as possible about ATCS oper- ations and deployments from previous studies. Finally, two electronic surveys were conducted: a shorter e-mail survey Surveys for ATCS vendors and a longer website-based survey for ATCS users. The survey conducted under this study had two components. The first was a request sent by e-mail to all major ATCS devel- opers or vendors to provide accurate and up-to-date descrip- Selection of Adaptive Traffic Control Systems tions of their systems. The ATCS vendors were requested to and Adaptive Traffic Control Systems' provide descriptions of the adaptive logic, hardware and soft- Deployment Agencies ware requirements, system architecture, detection require- More than 20 different ATCSs have been developed during the ments, and other special features of their systems. Most of the last 30 years. However, only about a dozen of them have been ATCS developers and vendors responded by identifying key applied in the real world and have more than one field imple- studies that best describe their systems. Some ATCS vendors mentation. In this study, it was decided to focus effort only on and users provided specific descriptions that they wanted to be those systems that are implemented in the field. There were a part of this study. These descriptions followed the requested few international systems that were not possible to describe in format but were sometimes broader than the scope of this detail because their developers/vendors did not express inter- study and therefore were edited. est in participating in the study. As a result, five U.S. and five international systems were investigated. Seven of those 10 sys- The second component of the survey was a questionnaire tems are deployed in the United States, whereas the other three that included quantitative and qualitative questions and was systems are currently deployed in Europe. The ATCSs con- delivered through a web-based survey tool. A link for the ques- sidered in this study are ACS Lite, BALANCE, InSync, LA tionnaire was sent to all ATCS users identified in the previ- ATCS, MOTION, OPAC, RHODES, SCATS, SCOOT, and ous task and responses were collected over 3 to 4 months. The UTOPIA. questionnaire was designed to gather as much information as possible on major North American ATCS deployments. It Selection of the agencies that deploy ATCSs was straight- had several sections (e.g., system requirements, operations, forward because the intention was to interview representa- training, and costs), each of which contained multiple ques- tives from all public agencies in the United States that operate tions. The questionnaire was designed to include both multiple- ATCSs. However, identification of these agencies was a choice questions and open-ended questions. Multiple-choice somewhat difficult process because there is no single source questions were used when there was some certainty that the containing such information. Therefore, identification of the suggested answers adequately represented the range of likely ATCS agencies was based on the literature review and com- answers. The option to add an answer was provided frequently. munications with traffic signal professionals, among which Open-ended questions were used when there was uncertainty the study's panel members provided important assistance. as to the anticipated answer. The final version of the question- naire (slightly different than the one offered on the web, owing to technical modifications that the web version requested) is Literature Review provided in Appendix A. A comprehensive literature review on ATCSs included the use of print and online resources such as Transporta- AGENCY PARTICIPATION tion Research Information Services (TRIS), Transportation Research Records, and ASCE and Elsevier websites. Among The survey was originally distributed to 42 agencies that run the documents reviewed, some provided general descriptions ATCSs in North America (United States and Canada) and of ATCS deployments and potential operational challenges. several dozen locations around the world. Numerous follow- Others were about evaluations of specific ATCS implemen- up requests were made, by e-mail and telephone, to encourage tations. In addition, few publications contained information those agencies that had not responded to participate in the sur- about the classification of ATCSs and conventional traffic vey. Table 1 is a list of those agencies that responded and the signal systems. There were many academic studies in which type of ATCS that these agencies operate. In a few cases, ATCS logics were evaluated in a microsimulation environ- respondents who were interviewed do not currently work for ment. Several documents from engineering conferences sum- agencies with an ATCS. However, they were recognized as marized the current status of ATCS deployments, with a future the best experts to answer questions about the ATCSs even