JUSTIFICATION FOR BUS LANES IN URBAN AREAS

This article summarises two studies in which theoretical models have been used to examine the economic justification of (I) with-flow and (II) contra-flow bus priority lanes. In each case, the benefits to priority traffic, in terms of savings in passengers' time and vehicle operating costs, were compared with the disbenefits to non-priority traffic which suffered some extra delay because of the priority scheme, and warrants were extracted which described the minimum flow of buses and bus passengers required to justify any particular scheme. In general, with-flow lanes only give considerable benefits when they are installed on the approaches of very congested intersections, while contra-flow lanes are more likely to be beneficial in situations where the available intersection capacity is not overloaded. It is important to design with-flow lanes in such a way as to minimise any capacity loss in the road system, and the extension of the priority treatment to other categories of vehicle, can in some cases, increase the net benefit obtained from the scheme. Contra-flow lanes can be justified by very low bus flows if they are installed in situations where the more complicated junction layouts required to cater for them do not delay the general traffic appreciably, but where the junctions are controlled by traffic lights the reserved lanes may require modification of the signal phasing in a way which reduces the junction capacity considerably. Where the junctions are controlled by roundabouts or channelisation, however, additional delay to non-priority traffic is likely to be slight.(a) /TRRL/