Physics + MathPhysics & Math

# To Move Faster, London’s Tube Needs to Slow Down

ByNOVA NextNOVA Next

Receive emails about upcoming NOVA programs and related content, as well as featured reporting about current events through a science lens.

London’s Underground needs to take a breather.

The subway—known affectionately as the Tube—is one of the world’s busiest systems, and it’s current average speed of 21 miles per hour may be too fast to keep people moving as quickly as possible, according to the results of new simulations

published in the Royal Academy Interface . Rather, the average system speed should be cut to 13 miles per hour, or about 20% faster than traveling by car.

The Tube runs into trouble because many passengers transfer to and from cars at stations outside the city, leading to congestion at the periphery of the sprawling system. The other system the study’s authors compared—New York’s subway—is more centralized and so doesn’t suffer as much when people pile up on the edges of the network. The difference—centralized vs. decentralized—means that, unlike the seemingly contradictory solution for London, people could move more quickly in New York if the trains sped up.

Here’s Jonathan Webb, reporting for BBC News:

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

Then, they connected these two layers based on the proximity between streets and subway stations. “We create these connections, and then we make an assumption, which is: When someone wants to go from A to B, they look for the quickest path – whatever the mode.”

Using this relatively simple system, the researchers measured various aspects of the “connectedness” of different points in the two networks.

The congestions occurs when both the road and train networks are examined together. Since people on the edge of the network often take a car or bus to a train station, studying the interplay between these two modal types is key to understanding how people move through both systems, Barthelemy and his colleagues argue.

Their study, however, relies only on maps of the networks and not actual passenger data. Adding that in could change the results, though the overall message of the “unintended consequences” that occur when two networks combine may remain the same.

London’s decentralized subway system may have played a role in the city’s development as a significant hub for commerce, Barthelemy and his colleagues say. The Tube allows residents to work in the city center but live on the periphery, and that may have freed up land in the city for commercial enterprises. While they didn’t study that link directly, “our results seem to go in that direction,” they write.