Degeneration: Hammersmith Bridge Closure
REES J and WILLIAMS T, London Transport Buses
While it has long been accepted that changes to land uses brought about by a new road can generate increased traffic, it was only in 1994 that the view that the road itself could lead to more traffic became widely accepted. The Department of the Environme
While it has long been accepted that changes to land uses brought about by a new road can generate increased traffic, it was only in 1994 that the view that the road itself could lead to more traffic became widely accepted. The Department of the Environment, Transport and the Regions (DETR) advisory group SACTRA (The Standing Advisory Com_m.ittee on Trunk Road Assessment) concluded that 'induced' (that is derived directly from the existence of new infrastructure) traffic really did exist, although they found that the effects could vary.
The inevitable question then is, if extra highway capacity induces extra traffic what happens when capacity is reduced? Now that the Road Traffic Reduction Act has placed the principle of traffic reduetinn (or at least a reduction in the rate of traffic growth) firmly on the political agenda, decision makers need to consider what happens to traffic when highway capacity is reduced; does congestion become unmanageable, does traffic disappear, i.e. degenerate, or what happens?
This question is of particular interest to London Transport Buses in light of the widespread interest expressed by many London Boroughs to re-allocate roadspace in favour of more environmentally fi'iendly modes such as buses, pedestrians, and cyclists. Assessment of bus priority measures generally requires that a minimal impact for non bus traffic occurs, thereby limiting the potential for bus priority schemes to radically improve bus travel.
Using the current evaluation techniques, giving over significant amounts ofroadspace to buses is likely to result in predictions of an overall increase in congestion over a wide area as traffic diverts onto other routes. It is, however, possible that traffic does reduce following the introduction of a radical bus priority scheme, or disappears (degenerates) rather than simply diverting or accepting an increased delay. In this case the method of assessment should take this into. account, making innovative and comprehensive bus priority measures a possibility.
There has been a growing desire amongst policy-makers in recent years to re-allocate roadspace away from general traffic and towards pedestrians, cyclists and public transport users, with the resulting need to assess the potential effects of doing so. The recent closure of Hamrnersmith Bridge to private cars and vans provided an ideal opportunity to study possible degeneration effects. London Transport Buses and the London Borough of Hammersmith appointed Accent Marketing and Research to undertake a survey with drivers who previously used the bridge. Drivers were invited to take part via a postcard distributed to them on the bridge two days prior to its closure and were subsequently interviewed by telephone to see how their travel habits have altered in response to the closure. Section Two of this paper reports the market research fmdings, while Section Three outlines some tentative findings in terms of the effect the closure has had on bus operations.
Association for European Transport