Shuttle working is used at bridges which must carry two-way traffic but are so narrow that only one lane is available. Vehicle entry to the shuttle lane is either uncontrolled, controlled by the use of priority signs or by traffic signals. This report presents a public road study of the way in which drivers share the shuttle lane and the resulting delays at narrow bridges which are unsignalised (uncontrolled or controlled by priority signs). A computer simulation model (calibrated from public road data) has been used to compare traffic delays using these unsignalised methods of operation with each other, with control by signals and with the same unsignalised methods of operation when used at roadworks under similar site and traffic conditions. The comparisons at narrow bridges indicate that delays are lower when entry to the shuttle lane is unsignalized than when simple signal systems are used. The comparisons of unsignalised systems at narrow bridges and roadworks show that the greater the degree of priority adopted by one stream of the traffic over the other, the greater the overall delay and the lower the capacity. The priority adopted by drivers in the two opposing streams is equal at narrow bridges with uncontrolled entry to the shuttle lane, and somewhat unequal when priority signs are used, though by no means as unequal as at roadworks. Enforcement of the signed priority at bridges (or roadworks) is likely to produce greater delays and much lower capacity than 'natural' operation provides. (A)

Want to know more about this project?