early in 1978 west glamorgan county council introduced a scheme for giving buses priority in central swansea. using selective detection (sd) equipment, buses approaching traffic signals are detected separately from other vehicles and the signal operation may then be modified to reduce their delay. part of the network was studied comprising a route passing through 6 intersections and one pelican crossing, all equipped with sd facilities. surveys were carried out with and without the priority in operation. over the length of the route studied, buses equipped for gaining priority saved an average of nearly 40 seconds with some gains in regularity. other vehicles lost an average of nearly 2 seconds each time they passed through a signal. theoretical estimates suggest that pedestrians waited at signal-controlled crossing places for an extra 1 second with priority. overall, priority saved bus occupants about 40 person-hours but lost other vehicle occupants and pedestrians about 90 person-hours over an average 10-hour day. about 60 per cent of the benefits and 80 per cent of the disbenefits occurred at one double-junction where, since the survey, changes have been made to signal settings to limit the disbenefit to other traffic. there are also unquantified factors which tend to redress the balance.(a)

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