Speed Limits

Speed limits

Fast and furious

Drivers are slowing down to save money

Jun 9th 2012 | from the print edition

WHEN the motor car was introduced to Britain in the 19th century, a top speed of 4mph was imposed so a man waving a red flag could run ahead as it entered a town. The laws of the road have changed as cars have become zippier. But, though vehicles are now faster, safer and more efficient, they are travelling more slowly, particularly on motorways. Why?

Compared with other European countries, Britain's top legal limit of 70mph on motorways and some dual carriageways is comparatively low. That may be one reason why 49% of drivers broke it in 2010, a higher proportion than almost anywhere else. Yet that figure is falling—in 2003 it was 57%. And in that time the share of drivers exceeding the limit by more than 10mph dropped from 20% to 14%.

Since motorway traffic has fallen, congestion does not explain increasing compliance. Nor does greater policing: stringent enforcement campaigns in France and Spain have successfully cut speeds, but Britain has seen a 20% drop in the number of traffic cops in the past decade, reckons Edmund King of the AA, a motoring lobby. Speed cameras have helped to maintain limits and cut accidents at roadwork sites, but are still rare on motorways.

Drivers seem to be slowing of their own accord. The main explanation is fuel prices, which have risen by 34% in real terms since 2003. This may affect behaviour because as cars go faster they use more fuel to travel the same distance—25% more at 70mph than at 50mph, according to the Department for Transport. In-car technology has also helped make drivers aware of such costs: new cars often have dashboard dials showing how many miles to a gallon the vehicle is achieving at its current speed. People are more likely to respond to such nudges when money is tight and jobs are scarce.

Just as drivers are choosing to slow down, though, the government is considering letting them...