Chicago's Computerized Traffic Control System

The computerized traffic signal control system consists of 73 intersections in an area approx 1 mile square. It replaces a fixed-time interconnected signal system that was installed in 1926. Magnetic loop vehicle detectors send traffic flow information to a central computer via city-owned cable. The computer is an Interdata 7-32 minicomputer with a 224 K byte main memory. The applications software consists of up to 15 pretimed signal timing patterns, as well as seven vehicle-actuated modes of operation. An operator interacts with the computer in deciding the correct mode of traffic operation. The system is presently being evaluated by the City of Chicago. Similar systems in other cities have proven to be beneficial in reducing both fuel consumption and pollution.