When average speed cameras were installed along the A9 last year, there was a mixed reaction. Danny Alexander, then the MP for Imverness, Nairn, Badenoch, and Strathspey, called it a knee-jerk reaction and said it was more important for plans to dual the road between Perth and Inverness to be brought forward. But Chief Superintendent Iain Murray, head of road policing at Police Scotland, defended the move and said the cameras would undoubtedly make the A9 safer for all road users.

Nine months on from the introduction of the cameras, there is now growing evidence for Mr Murray's prediction, but the figures also suggest that average cameras are at best a stop-gap until the road can be upgraded. Earlier this year, it was revealed the number of drivers speeding on the main road to the Highlands had dropped from one in three to just one in 20 and the number caught doing more than 10mph over the limit had fallen by an extraordinary 97 per cent. Clearly, the cameras were changing behaviour.

But on the question of whether they are making the road safer, the figures are nuanced. They do show that in the first six months of the cameras, the number of injuries on the road more than halved - just three people were seriously injured in the six months after the cameras were installed, compared with a previous average of 10, and 22 were slightly injured, down from an average of about 45. But the figures also show that, in the same period, the average number of deaths showed no improvement on the period before the cameras were installed.

What the figures put beyond doubt is the fact that drivers have slowed down dramatically on the A9 and that fewer people are being injured. But what they also underline is that speeding is not the only factor in collisions and only dualling the road will bring about more profound change to this dangerous road. No road in Scotland claims as many lives as the A9 and anyone who has driven it will find that unsurprising. It is a vital link in the Scottish trunk road network and yet it is a frustrating combination of single-track and dual carriageway. The dual stretches were introduced in an attempt to make the road safer but if they have helped ease the frustration of some drivers, they have merely added to the confusion of others. It all makes for a fatal combination on a long, dangerous road.

The good news is that the new figures show that slowing the road down through the use of average speed cameras has helped, but Danny Alexander was right last year when he said that it is more important to expedite the dualling of the road. Under current projections, the new dual carriageway will not open for more than a decade. But with speed cameras apparently failing to cut the number of deaths, it is more important than ever to start the project as soon as possible and finish it with the utmost speed.