AREA-WIDE PUBLIC TRANSPORT POLICY - A WARNING

Bus priority lanes with adequate setbacks at signals, carefully phased timings, and the right combination of vehicle flows and turning movements enable bus passengers to receive substantial time saving benefits but with no offsetting disbenefits of private road users. As flow intensities increase and junctions interact leading to queues and blocking back, something has to give. Choices then need to be made by planners over who should be given priority with limited road space. Emphasis is being placed on public transport priorities, including bus lanes, guided bus ways, selected vehicle detection at signals, so that the conditions for other road users progressively deteriorates. This leads to a greater tendency for private road users to switch to public transport and this state of affairs can be reinforced by traffic calming priorities in adjoining residential areas. Such a policy of positive discrimination is a legitimate aim and has been pursued in many European cities and is being considered by far more. However, a plausible but unacceptable consequence of these aims was encountered in recent work undertaken in a European capital. As public transport priority measures increased by the adoption of first priority (no setback at signals) bus lanes on major radial routes into the city centre, congestion increased to such an extent that not only did private vehicles reassign onto other routes but those other routes carrying high bus flows led to a net increase in delays for bus passengers as well as private road users. Subsequent work on network planning overcame this problem and a highway network prioritisation programme was recommended which gave major benefits for public transport passengers, disbenefits to private road users and was forecast to result in an overall 6% shift from private to public transport brought about by bus priority measures only. This work is described by using results from the SATURN model created for Dublin. The paper describes a particular set of circumstances and the way first priority bus lanes were modelled. Whilst the method cannot replace more detailed simulation of public transport priority measures and how they interact with non prioritised traffic, it does highlight the importance of considering the area wide implications of major public transport priority initiatives. (A) For the covering abstract of the seminar see IRRD 859670.