Road deaths fell below 3,000 last year for the first time since records began in 1926. The road network is now eight times safer per mile travelled than it was in 1966, when deaths reached a post-war peak of 7,985. This is a startling success, and good statistics are worth at least as much attention as that usually lavished upon bad ones.

Talk of success may sound odd when the topic is accidental death, since every death is a tragedy. Yet the figures matter. To use a phrase beloved of Boris Johnson, “it is all going horribly right”. Finding out why might help to continue or improve this trend. The answers may also have wider significance, shedding light in a debate where there is usually simply heat - helping to establish what actually works to improve safety.

What are the main areas for investigation? Naturally, the first is whether there has really been a great deal of improvement in road safety at all. It may be that better medical care, more effective at turning fatalities into mere serious injuries, is responsible for much of the drop in casualties: the fall in the number of collisions is only half that in the number of deaths.

An alternative explanation for this discrepancy is that vehicles have become a great deal safer, leading to fewer deaths upon impact. Driver and passenger airbags, ABS brakes and frontal protection systems have all made the roads less hazardous for drivers and pedestrians.

The fall in both deaths and collisions might be explained by a change in the speed at which drivers travel. Ten years ago a study found three quarters of drivers routinely broke the 30 miles per hour speed limit. Now only half do. Why has this happened?

Part of the answer, despite the controversy that attends them, is surely the introduction of road humps and safety cameras. A series of memorable road safety advertisements may have made their mark. Even those who argue that safety regulation makes little or no difference at all (an extreme position but with some adherents) are willing to agree that a change in attitude to speed helps. The campaign against drink driving has largely succeeded in turning a habit regarded, until relatively recently, as acceptable if unwise, into one that is socially taboo.

One further hint that social norms may play a role is that while the road is becoming safer for most, the casualty rate for young drivers has not fallen. Unlike older drivers, this group may be immune to the influences of campaigns and punishments and remain addicted to speed. The figures on young drivers also suggest that the inquiry need not spend too much time studying the new driving tests. They do not appear to be part of the success story.

A further area for examination is the change in the number of child deaths. The figures here are striking. Child deaths on the road fell by 28 per cent in 2007 compared with 2006. While it is to be hoped that these result entirely from parents strapping their children in more safely and then driving with greater care, there is another possible contributor. Children may simply be ferried by car to places they used to walk to, avoiding the risk of being run over - but contributing to a trend about which anti-obesity campaigners may not be particularly enthusiastic. This point is underlined by the cycling statistics: the number of adult cycling deaths increased last year while that of children halved, suggesting fewer are being allowed on their bikes.

Acting successfully to improve safety is notoriously difficult. Regulation may encourage evasion, and campaigns may normalise dangerous activity. The road initiatives appear to have navigated their way through these dangers. And that is worthy of celebration.