TRAFFIC EVAPORATION/ˈtræfɪk ɪˈvæpəˌreɪʃən/

It’s been known for some years that if you build a new road to meet expected traffic flows, the very existence of the road is a stimulus for traffic growth. This was obvious, for example, following the construction of the M25, the orbital motorway around London. But if building new roads generates traffic, it ought to follow logically that restricting access to roads should decrease it. And this is what has been found: a study from London Transport and the Department of the Environment, Transport and the Regions suggests that road closures do persuade many drivers to transfer to other kinds of transport, not just while congestion from the closure exists, but permanently, a phenomenon that’s been dubbed traffic evaporation by road engineers. It seems it happens when drivers have a choice of methods of travelling, swap to another such as public transport when their normal road route is closed, get used to travelling the new way, and don’t change back when it reopens. The report is predicted to have a big effect on roads policy in urban areas where there are more methods of transport than just the private car and may even encourage the creation of new public transport links in tandem with road restrictions.

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