Types of Traffic Signal Systems
Computerized traffic control signal systems are used to view and manage current traffic conditions, diagnose signal system problems and implement or modify signal timings remotely.
The City operates the two computerized traffic control signal systems.
TransSuite Traffic Control System (TransSuite TCS)
TransSuite TCS is a hybrid traffic control system that relies on second-by-second communication to monitor signal operations, but relies on field equipment to maintain signal coordination (i.e. the field equipment can maintain signal coordination for about 24 hours if there is a loss of communication). TransSuite TCS does not directly control signal movements, but commands each intersection controller (computer) to follow the timing plan that resides within its local database. TransSuite then verifies that the controller adheres to the commanded timing plan. TransSuite TCS can accommodate up to 256 signal timing plans. In practice, we generally implement five plans – morning peak, afternoon peak, midday off peak, night and weekend.
Split Cycle Offset Optimization Technique/Urban Traffic Control (SCOOT/UTC)
SCOOT is an adaptive traffic control system that determines its traffic timing plans based on real-time information received from vehicle detectors located on the approaches to signalized intersections. SCOOT relies on telephone communication to maintain signal coordination. UTC is a traffic control system that operates in tandem with SCOOT; it also relies on telephone communications. UTC provides pre-determined signal timing plans and is used as a stop gap measure if SCOOT is not available. SCOOT signals are sometimes called “smart” signals.
The existing Split Cycle Offset Optimization Technique (SCOOT) system is close to the end of its useful life – the equipment is aging, it is hard to get replacement parts, the intrusive SCOOT (loop) detectors are susceptible to road work and repairs are not keeping up, and the old communications infrastructure makes it difficult to communicate with the signals in the field. New technologies are now available that will help the City to overcome these problems. The City is evaluating two technologies to determine which works best for Toronto.
At 10 locations on Yonge Street between Yonge Boulevard and Castlefield Avenue, the City is piloting a technology called InSync, which is used in the United States. This technology makes decisions based on video-analysis camera detection that measures vehicle delays and queue lengths on the approaches to the signalized intersection and relays that data to the intersection computer which then determines and implements the best timing plan in real time.
At 12 locations on Sheppard Avenue East between Neilson Road and Meadowvale Road, the City is piloting a technology called Sydney Coordinated Adaptive Traffic System (SCATS), which is used in Australia, Asia and the United States. This technology makes decisions using radar detection to measure traffic flow and downstream of an intersection and then uses an algorithm to determine and implement the best timing plan in real time.
The performance and effectiveness on InSync and SCATS will be measured by comparing before-and-after conditions relating to traffic volumes, travel times, pedestrian delays, stops and side street delays. In addition to newly installed vehicle count stations and Bluetooth detectors, City staff will also use commercial GPS data in the evaluation. The output of the pilot study will allow the City to identify the technological solution that offers the best cost and benefits for the City.
The history of traffic signals and signal systems begins with the busy intersection of Bloor Street and Yonge Street. It was home to Toronto’s first traffic signal in 1925. The following year saw the installation of signals at many more intersections.
The introduction of computers into the realm of traffic control was pioneered in Toronto in 1959. Metro Council has concluded that improvements to traffic signal control were needed to complement the rapid expansion of the arterial road network. Metro Council authorized a small-scale pilot study to examine the practicality of introducing a new traffic signal system which could be centrally controlled through the use of an electronic computer.
At the time, only specialized analog type equipment was available in the industry, and this would result in huge costs to replace signal controller hardware, with limited opportunity to introduce innovative strategies in either the theory or practice of traffic control. A research report suggested that if a general purpose digital computer was operated in real time, it could take in traffic information from a large number of vehicle detectors, select timings and offsets, and optimize these for overall system efficiency. Although this suggestion appeared attractive, some doubts were expressed concerning the ability of a digital computer to perform in the required manner. Therefore, a network of 15 signals was controlled in various ways ranging from pre-timed to fully traffic responsive to test the feasibility. This proved to be so successful that it was decided to proceed with the full scale system.
Metro proceeded with the installation of the world’s first full-scale, real-time, automatic traffic control computer in June 1963. A key to success was that the Metro Roads and Traffic Department had been granted authority over all existing or new signals within the then Metropolitan Toronto. The first phase of the system required the installation of 1,000 vehicle detectors, and the connection of each controller through leased telephone lines to the computer, which was located on the main floor of the Old City Hall. In a comparative sense, it was the second largest on-line control system in the world, exceeded only by the North American Air Defense Command (NORAD) installation.
Initially the system was responsible for 500 signals, but as Metropolitan Toronto grew, so did the number of signalized intersections that were to be controlled. Unfortunately the original traffic computer was capable of controlling only 1,164 intersections, and Toronto soon surpassed that figure as the city experienced rapid growth. In 1978 it was decided that a replacement system was necessary. This new traffic control center was located underground as part of the Sheppard subway station on the Yonge Line. It became operational in the early 1980s.
By the mid-1980s, the capacity of the Gardiner/Lake Shore corridor had reached its limit. A feasibility study confirmed the benefits of installing a corridor traffic management system (CTMS). Construction of the CTMS was approved in 1987 by Metro Council. However, around the same time it was becoming apparent that Toronto could benefit from the development of an Integrated Traffic Control Centre (ITCC) which would combine the operation of the corridor system with the traffic signal control system. The implementation of this ITCC was subsequently approved in 1989.