The government is absolutely right to extend the coverage of speed cameras as they have a proven record of reducing road accidents where they have been installed. The only qualification is why they are only being extended to four new areas - North Wales, Derbyshire, Lancashire and Staffordshire.

If they are as effective as the statistics show - an 18% fall in the number of people killed in the areas where they have been in operation - then they should be available as widely as possible throughout the land.

The revised scheme announced yesterday enables the police to plough back the money raised from speeding fines into the construction of more speed traps (subject to certain conditions). It also enables the police to lower the threshold at which the cameras start to click. In future a 30mph limit might be triggered at 35mph, instead of 40mph at present.

Many motorists will be enraged by further intrusions on their "freedom" to drive. Already critics are saying that the benefits of the scheme could be offset by drivers speeding until they come within range of the cameras (which will now be more clearly painted) only to put their brakes on, thereby causing cars behind to stop suddenly. Maybe, but the benefits, in terms of saving lives, are so huge compared with the side effects that such objections should be ignored.

People have a curious attitude to road accidents. The death of four people as a result of the Hatfield rail disaster - horrific and avoidable though it was - has resulted in hundreds of millions more being spent on railways to make them safer. That is good.

But it is also true that, if saving lives were the criterion, money is far more effectively spent on preventing accidents on the roads because modest amounts spent on reducing speed limits in association with other traffic calming measures can have a dramatic effect on casualty statistics. The government should expand this scheme across the whole country as quickly as possible.