The stated objective of this investigation was to develop, calibrate and, as far as possible, validate a behavioural model of drivers' responses to the changing of traffic signals at the end of the green phase, the model being so formulated that it can be used to estimate the effect on drivers' responses of a range of possible modifications to the way in which the signals change from green for one set of streams to green for other conflicting streams, allowing for the possibility of risk compensation. As reported here, many important behavioural, physical and mathematical elements of such a model have been specified and a good deal of calibration has been undertaken. Validation with data not used in the development and calibration of the elements of the model has not proved practicable within the available resources. The method adopted was a combination of: (a) recording and analysing of the movement of vehicles on one approach to each of three signal-controlled junctions; (b) observation and analysis of responses of subjects placed in a laboratory situation simulating the approach to a signal which changes from green; (c) task analysis of the task of driving through a signal-controlled road junction safely and with minimal delay; and (d) mathematical analysis of the situation faced by a driver approaching a signal which changes from green through amber to red. All parts of the study concentrated on vehicles proceeding straight ahead, the laboratory studies simulated approach speeds of 30, 40 and 50 miles/h and the three junctions chosen for observation had roughly corresponding speeds of approach.

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