Adaptive control software for distributed systems

Traffic control systems in the United States evolved from electro-mechanical time-clock based to computer-based in late 1970s. The research and development sponsored by the Federal Highway Administration resulted in mainframe computer based centralized systems called Urban Traffic Control Software (UTCS). The key aspects of these systems were second by second command and control by the central computer of electro-mechanical controllers at each intersection. The communication technologies at the time were twisted pair time division multiplexing with a maximum of 12 intersections per pair of communication cable. A majority of the urbanized cities in the U.S. implemented such systems. In the 1990s, the Federal Highway Administration (FHWA) started research called adaptive control software (ACS). This research generated four adaptive traffic control software prototypes called RHODES, OPAC, RTACL and ATCS. The key aspect of the RHODES, OPAC, and RTACL is that the control software is decentralized with link by link short time prediction of traffic demand. ATCS extended the UTCS approach to include adaptive capabilities. This research constitutes a major advancement in traffic signal control since the deployment of UTCS.