When traffic signals change from green, drivers have to decide whether they can safely stop or continue and clear the stop line before the start of the red light. The length over which decisions are difficult is termed the dilemma zone. Research by TRL was used as a basis for recommendations for additional detection for speed control at junctions on high-speed roads. The speed of approaching vehicles was measured and used to calculate when the vehicle would reach the outer limit of the dilemma zone. Before the driver reached the dilemma zone it was safe for the signals to change, but once in the zone, they would be given a fixed extension of the green time. Details are given of the speed assessment (SA) and speed discrimination (SD) systems and their associated equipment. The MOVA (microprocessor optimised vehicle actuation) signal control system is described. Signal control at high-speed sites in urban traffic control regions is discussed. Signal head alignment is considered.
Samenvatting