Some jurisdictions have maximum cycle times. The cycle time is the time it takes for a cycle to complete. ![]() A cycle is one complete sequence of stages. For example, a crossroads with four approach arms could operate in two-stage operation, where each road is given green, or three-stage operation, where the major road is given green, then each side road is given green in turn. Stages and periods Ī stage is a group of non-conflicting phases which move at the same time. Normally, conflicting movements are not permitted, except for opposed right or left turns (depening on driving side) or, in some jurisdictions, pedestrians and vehicles moving in parallel directions. A movement is conflicting if these paths cross one another. Ī movement is any path through the junction which vehicles or pedestrians are permitted to take. In the UK, a filter phase allows non-conflicting traffic to make particular turns (normally left or ahead) through a junction. For example, a green phase gives all traffic from a particular approach the right of way through the junction (bar turning traffic). Phases are indications shown to traffic on traffic signal aspects (a single light on a signal head). Moving phases are shown in green and stopped phases are shown in red. ![]() The phases operate together in three stages (1, 2 and 3). Phases This three-arm signal controlled junction has three vehicle phases (A, B and C) and a pedestrian phase (D). PTV VISSIM also uses the signal group terminology. One electrical output from the traffic signal controller is called a "signal group" - similar to the UK and USA concept of "phase". A "phase" is a period of time during which a set of traffic movements receive a green signal - equivalent to the concept of a "stage" in UK and USA. ![]() In Australia and New Zealand, the terminology is different. The first automated system for controlling traffic signals was developed by inventors Leonard Casciato and Josef Kates and was used in Toronto in 1954. A variety of different control systems are used to accomplish this, ranging from simple clockwork mechanisms to sophisticated computerized control and coordination systems that self-adjust to minimize delay to people using the junction. The normal function of traffic lights requires more than sight control and coordination to ensure that traffic and pedestrians move as smoothly, and safely as possible. The various vehicle and pedestrian movements are separated in either time or space for safety and efficiency. A junction for road vehicles and pedestrians controlled by traffic lights in the UK.
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