Arterial priority option for the TRANSYT-7F traffic-signal-timing program.

The objective of this research was to modify TRANSYT-7F so that arterial priority can be increased and minor-movement performance degradation can be controlled. The product is known as TRANSYT-7F with arterial priority option (APO). TRANSYT-7F "globally" minimises overall stops and delay to all vehicles. This is satisfactory for a grid network on which good traffic performance is desired equally for every street. However, it is unsatisfactory for arterials on which progression for the through movement typically is considered much more important than minimising stops and delay for left-turning and side-street motorists. In the united states, TRANSYT-7F is widely perceived as unsatisfactory for arterial signal timing. TRANSYT-7F with APO modifies the iterative-search process to give priority to the arterial. APO changes the optimisation process, not the traffic flow model. In general, the user specifies which links are to receive priority and the degree of saturation for the minor movements (nonpriority links). The performance index (PI) equation is formulated to minimise stops and delay for only the priority links. The degree of saturation specified by the user for the minor movements is used to control the performance degradation to acceptable levels. The results of a program run may be used to make changes to the list of priority links and to the required degree of saturation of one or more nonpriority links on the basis of the engineer's judgement. APO is thus user interactive; the engineer retains control over the optimisation and can tailor it to local conditions.