A version of SCOOT has been developed which incorporates bus priority. The logic of bus priority is contained within the SCOOT kernel which has been modified by TRL. The bus priority optimiser implements green-time extensions and priority recalls; the decision to make an extension or recall and the limits imposed on them is decided with reference to the degree of saturation or spare capacity of the network, and so makes full use of SCOOT capabilities. Buses are modelled and account is taken of queues which may delay buses. Simulation tests showed savings in bus passenger delay of typically 20% to 30%, with greater levels being possible at lightly trafficked junctions. In one simulated network, extensions were shown to produce savings of about 24% in bus passenger delay with the least disruption to other traffic (no significant increase in car passenger delay); recalls produced further savings of about 8% in bus passenger delay but were more disruptive to the other traffic (about 4% increase in car passenger delay). The simulation produced recommendations for the SCOOT system to be tested during the field trials, covering the target saturation levels and recovery logic to be used. The SCOOT bus priority system has been installed in London and Southampton. In London, buses have been fitted with transponders and special bus detectors are installed in the road at ten junctions in Camden Town. The central computer contains the new SCOOT kernel, and logic to perform local green extensions for bus priority has been included in microprocessor controllers. Southampton uses the same SCOOT kernel, but connected to a GEC Bus-Tracker AVL system to provide bus detection. Nine junctions in Southampton have been configured to allow bus priority within SCOOT. A field trial in Camden Town, London showed bus delay savings averaging 5 seconds per junction (22%). The maximum delay saving to buses was achieved using local extensions and central recalls. Delay to other traffic was small with local extensions at all traffic levels, but recalls at higher traffic levels caused disbenefit to other traffic averaging 5 seconds per vehicle. (A)

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