SINCE 2000 London has seen around 40 strikes on the Underground. The chaos which accompanies them is a short-term drag on the capital’s economy. The Federation of Small Businesses, an industry body, estimated that the one-day strike in July cost London £300m ($462m). But a new paper, by researchers at the universities of Oxford and Cambridge, points to the long-term benefits of tube strikes. The focus of the paper is Londoners’ commuting patterns, before and after industrial action takes place. It looks at a two-day strike in February 2014, which the National Union of Rail, Maritime and Transport Workers called in response to plans to close ticket offices and make voluntary redundancies. In that strike, some union members continued to work: the effect was that 171 out of 270 tube stations closed for the day. Some commuters were not much affected by the strike, while others were less lucky.

The authors compare the behaviour of those hit by the strike to those that were not. To do so, they gather anonymised data from Oyster cards, the payment gizmos that Londoners use to enter and leave the tube. They end up with data on about 18,000 Londoners over a 20-day period who used the Underground between 7am and 10am, amounting to more than 200m data-points.

The results are surprising. Eight in ten commuters were forced to change their commute during the strike—either because stations were closed or because congestion was unbearable. Of that group, about 5% decided to stick with it once the strike had finished.

Before the strike, it seems, many Londoners had unwittingly been taking a suboptimal route to work. The tube map, designed by Harry Beck in 1931, is unrepresentative of absolute geographical space; in his lifetime Beck was pilloried for showing Wimbledon and South Wimbledon to be miles apart, when in fact it is a short walk from one to the other. Add to that the different average speeds at which trains hurtle along—the Waterloo and City line goes at 47 km/h, compared to 15km/h on the Hammersmith and City—and it is small wonder that many commuters choose the “wrong” route.

Commuters affected by the strike, the authors find, in subsequent days enjoyed a 20-second shorter trip on a one-way commute. Over time, the authors estimate, the benefits of that shorter commute were worth more than the damage caused by the strike. 