01172018

Study suggests Tube is ‘too fast’

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Could slowing down the Tube decrease congestion levels?

A mathematical study of transport in London and New York suggests the British capital should be wary of its trains travelling too quickly.

If Tube journeys are too fast, relative to going by road, then the model predicts an increase in the overall level of congestion.

This is because key locations outside the city centre, where people switch transport modes, become bottlenecks.

By contrast, New York’s layout is such that faster trains will always help.

Reporting their findings in the journal Royal Society Interface, the researchers calculate that London’s system would function best with underground trains travelling about 1.2 times faster than the average speed on the roads. This makes the optimum Tube speed approximately 13mph (21km/h); the current average is 21mph (33km/h).

But Dr Marc Barthelemy, the paper’s senior author, said it was a theoretical study and more data would be required to make specific recommendations.

“Giving exact numbers is a tricky thing,” he told the BBC. “But the fact is that these networks are coupled to each other. Optimising something on one network can bring bad things on another network.”

‘Multimodal’ movement

Dr Barthelemy, a statistical physicist at the CEA research centre in Saclay, France, is fascinated by the interplay between coupled networks. And transport networks, such as the roads and train lines in his study, are becoming increasingly interconnected.

In a report on urban mobility published on Tuesday, the LSE Cities group at the London School of Economics describes a trend towards “multimodal” journeys, where travellers switch – for example – from train to bus or car.

This is partly driven by smartphones and apps which search for the fastest route, even if it involves a change or two. But in big, expansive cities like London, multimodal trips are inevitable, Dr Barthelemy said.

“In London there’s a clear increase in the number of modes with distance,” he explained. “It’s a very clear effect.”

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Longer journeys in London tend to involve more than one mode of transport

To test how these different transport networks can affect each other, he and his colleagues built computer models based on the exact structure of the road and underground train networks of both London and New York.

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