One method of giving buses priority at traffic signals is known as selective detection (SD): buses are detected in a mixed traffic stream and allowed to extend an existing green signal or to recall a green signal earlier than normal. A computer simulation model has been used to study junctions with three traffic stages or with two traffic stages and a pedestrian stage. A range of bus and other vehicle flows were simulated. Although buses could be given substantial benefits (up to 30 seconds in some circumstances), other vehicle journey times were increased, sometimes very substantially. The most suitable method of applying SD priority in a particular situation depends on the selection criterion adopted (e.g. minimisation of total passenger journey time). such a criterion may well require a limitation to be placed upon the extra journey time of other traffic, which in turn may prevent the full bus benefit from being realised. Detailed results are given and tables are presented suggesting appropriate priority methods for the cases studied and associated bus benefits. It is concluded that SD priority is useful for a wide range of conditions. An analytic method for estimating bus benefits is also described and estimates are tabulated. (Author/publisher)
Abstract