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6 only two of those were successfully tested and implemented for their more extensive deployments. German systems were in the field: a modified version of OPAC and RHODES (Real- facing a series of local institutional barriers and were seen by Time Hierarchical Optimized Distributed and Effective Sys- the professional community, for a long time, only as scien- tem) (Head et al. 1992; Mirchandani and Head 2001). It is tific research tools (Mueck 2005). It was not until the late interesting to note that one of the first fully operating North 1990s that their benefits were recognized by traffic signal American ATCSs, the Los Angeles Department of Trans- practitioners. Two major characteristics make German ATCSs portation (LA DOT) ATCS, was not part of the RT-TRACS distinctive: they attempt to address optimization of traffic sig- project, but was developed independently in 2003 by the city nals based on network-wide changes in traffic demand by tak- of Los Angeles. ing into consideration the estimated origindestination flows in the network, and their logics are adjusted to work with Although early tests showed significant benefits of deploy- German industry standards for local traffic controllers and ing OPAC and RHODES over fixed-time and actuated-traffic public transit priority. control, these two systems were not widely accepted in the United States. It appears that the major reasons for the lim- To summarize, ATCSs have been used since the early ited deployments of these systems (as well as of all other 1980s. Although there are at least 25 ATCSs deployed in the major ATCSs) are the complexity of their logics, extensive United States, these systems may not be well understood by detection requirements, necessary hardware upgrades, and many traffic signal practitioners in the country. Their opera- the need to acquire new knowledge; in short--increased costs tional benefits have been demonstrated in several cases, but of operations and maintenance. To respond to these issues some professionals argue that the systems are no better than the FHWA launched the development of another ATCS whose good time-of-day (TOD) actuated-coordinated plans. Other major role was to be more simplistic, user-friendly, compat- issues with ATCSs include detector maintenance and com- ible with existing infrastructure (detection and hardware), and, munications problems and overall that these systems are con- overall less expensive to operate and maintain. The system is sidered expensive and complicated (Crenshaw 2000; Hicks called ACS Lite and, although it has been tested in the field and Carter 2000). Previous surveys on ATCS implementa- at four locations throughout the United States, is undergoing tions provided some of the underlying sources of agencies' further enhancement (Shelby et al. 2008). reluctance to widely deploy these systems. One of the major purposes of this study is to provide insight into all these issues During this same period, SCOOT and SCATS were going from the perspective of an ATCS user to explain why ATCSs through their own challenges with installations in the United have not been utilized more, especially in the United States. States. Although their deployments in Europe, Australia, and Asia have steadily increased over the years they have strug- STUDY GOALS AND OBJECTIVES gled to increase their deployments in the United States. It appears that the major problems of early SCOOT and SCATS The goal of this study was to summarize the state of practice deployments in the United States were related to hardware in deploying ATCSs in North America, with an overview of and software, which were not fully customized for the U.S. ATCS deployments around the world. In this study, a broader market. Early problems with National Electrical Manufac- definition of an ATCS was adopted to include all systems that turers Association (NEMA)-incompatible traffic controller adjust their signal timings in real time based on changes in cur- hardware caused problems with some SCATS deployments in rent traffic conditions (excludes actuated and traffic-responsive spite of the evident operational benefits. Some SCOOT deploy- pattern-selection systems). This study adopts an ATCS defini- ments faced similar problems: suboptimal (for SCOOT oper- tion that includes all systems defined as traffic-responsive ations) detection placements and somewhat user-unfriendly and traffic-adaptive control under the third generation of traf- Open Virtual Memory System (VMS) interface negatively fic signal control systems (Gordon and Tighe 2005). impacted SCOOT operations at some deployment sites. The goal was achieved through the following objectives: Across the ocean, continental Europe struggled for a long time to keep up with the development of ATCSs in the United Describing operational characteristics of major ATCS Kingdom, Australia, and America. French systems, such as deployments; CRONOS (Boillot et al. 1992) and PRODYN, which were Identifying and describing widely deployed ATCSs, early ATCS leaders in continental Europe, were not widely including a description of their working principles and deployed in France or elsewhere. UTOPIA/SPOT appeared operational requirements; to work well in the networks of Italian cities for many public Identifying operational advantages and disadvantages of transit operations, but the first SPOT deployment abroad, in deploying ATCSs, along with the problems with imple- an environment with mostly vehicular operations, was not mentation and lessons learned; successful (Pesti et al. 1999). Development and application of Identifying institutional problems at agencies that deploy German ATCSs, where SITRAFFIC MOTION (Kruse 1998) ATCSs, along with documenting their experiences; and and BALANCE (Friedrich et al. 1995) represent the most Investigating implementation costs and benefits per- notable systems, suffered for years before conditions were met ceived by ATCS users.