TRAFFIC STUDIES ON THE SEVERN BRIDGE

Abstract

The methodology presented is based on a case-study, relating to the most important and heavily-used toll bridge in Britain--the Severn Bridge, which forms part of the motorway system linking London with the south-western part of Britain--but the techniques used are applicable with a little modification over a wide range of different toll systems. The Severn Bridge has had structural and maintenance problems which have caused lane closures to be a regular feature. At peak periods of the year delays of several hours occur, and queues over 17 miles long have been recorded. Planning and building of a new bridge is likely to span about 15 years, and the degree of congestion which may be expected towards the end of the century is considered. In this paper descriptions are given of mathematical and simulation models which may be used to estimate vehicle delays and queue sizes under a variety of flow levels and operating conditions. Estimates are given for the vehicular capacity of the bridge, and a cost analysis is presented comparing delay costs with toll income. (Author/TRRL)