The chapter describes various aspects of the traffic signal control of isolated junctions, outlines elementary traffic signal theory, and considers many illustrative examples of specific junction designs. Traffic signal hardware consists of a set of signal heads and vehicle detectors, linked by cables to a signal controller, which is programmed to control the signal indications. A junction and its signal control are designed so that the junction operates in a safe and efficient way that road users perceive to be fair. Safety depends on user compliance, which in turn depends on perceived fairness, which is generally achieved by a maximum red time and a minimum green time in each traffic lane. Traffic streams approaching the junction are grouped into stages which can receive green simultaneously. Signal timings are generally determined by first fixing a cycle time that offers adequate capacity, then allocating green times to the different stages within the cycle time. Elementary theory assumes that the capacity of the junction is sufficient to allow settings for which no stream has saturated traffic flow; it does not cover the oversaturated case where congestion is too great to make such settings possible. The chapter also discusses performance measures, off-line signal plan generation, and on-line junction microcontrol. For the covering abstract, see IRRD 892228.
Abstract