the computer simulation (buspas) was designed to assess those bus priority techniques which can be used when buses are selectively detected in a mixed traffic stream. it was developed from an existing trrl simulation; individual vehicle journeys are modelled, and a record is kept of each bus journey. special detectors simulate selective bus detectors and the particular priority technique under investigation is specified by the user. both the benefit to buses and the disbenefit to other traffic are predicted. predictions of delay from buspas were compared with the limited amount of experimental data. the agreement was satisfactory (typically within 3 seconds) but all the effects of the bus priority were small. buspas has not been validated for situations where bus priority causes large changes in journey times. normally buspas uses a binomial distribution of vehicle arrivals but more bunched distributions have been tested. a measure of the degree of bunching of the traffic is output for each approach to the junction. the two variance reduction techniques which were used when testing buspas are recommended for routine use. to simulate 2 hours of real time with total flow through the intersection of 3600 vehicles an hour took about 15 minutes of elapsed time on an icl 4-70 computer.(a)

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