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Traffic Impact of Highway Capacity Reductions: Assessment of the Evidence

S. Cairns, C. Hass-Klau, P. B. Goodwin

In 1994, a government committee report showed that building roads could generate traffic. Since then, there has been a lot of interest in whether the opposite is true – can reducing road space for cars cut traffic? This could be particularly important when introducing policies like bus lanes, which could provide a cheap and effective way to improve the attractiveness of public transport, but which would be untenable if displaced traffic brought neighboring roads to a standstill.

Therefore, London Transport and the Department of Environment, Transport and the Regions (DETR) commissioned research to investigate the question, and employed a team at University College London (UCL) to look at the evidence, and the consultancy MVA to look at the modeling implications. Consequently, the UCL team examined nearly 60 locations where road space had been taken away from cars and put to other use. In some cases, road space for cars had been reduced because of deliberate policies like bus lanes or pedestrian infrastructure, in others it was because of problems like roadwork. Irrespective of the cause, in such circumstances, there are often predictions of major traffic chaos. Examination of the evidence suggested that these predictions rarely, if ever, prove accurate. Prolonged, long-term gridlock is simply not reported, although there can be short-term disruption, and some increase in problems on particular local roads. In many cases, there were actually significant reductions in the total amount of traffic on the networks studied.

Updated: 6/20/2017
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