I have observed with great interest the correspondence about upgrading the A9 to dual carriageway status between Perth and Inverness. I understand the frustrations expressed. As a user of the road, I share those feelings, but there are aspects of the case that, as yet, have not been discussed.

Murdo Fraser, the Conservative MSP, makes repeated demands for the road to be dualled. He is, however, hardly the best person to address this issue since the road, as presently configured, apart from recent changes such as the Ballinluig junction, is largely the creation of his own party which was in government when it was built.

I find myself driving the A9 between Dunkeld and Kincraig. I have studied the road and wondered why certain parts are as they are. Why, at various places, are there broad flat areas parallel to the carriageway which run for miles? Why are there long bends which exhibit what engineers call "continuous radius curves", bends on single carriageway sections that go on for long distances at the same curvature so that drivers cannot see round them?

I have talked to roads engineers and their view is that the road was designed as a dual carriageway but was not built as such. This is based on their belief that no roads engineer would build a single carriageway main road with that type of curve. Such bends present a significant danger because of the lack of forward visibility. If people lose patience, as they do, and decide to overtake despite not being able to see far enough ahead, they often end up in head-on collisions.

As to the mystery of the long flat parallel areas, these are where a second carriageway was intended but was never built. Why? Money, of course. There is understandable pressure on the Scottish Government to dual the road. However, realism is required to address serious problems, one of which is topography. In many places, I simply do not see where a second carriageway could be built adjacent to the exisiting one. You can erect overhead sections, span gullies with bridges and so on, but in some places there is no space to do even that. The only option will be to have the north and southbound carriageways separated over several long stretches.

There may be no technical difficulty about that, if the land can be acquired, but there would be major, very costly, compulsory purchase orders. Other consequences would flow. For example, if you have an accident on one carriageway but the nearest emergency services only have access to the other, from whence does help come? Link roads would have to be built where the carriageways were separated and, probably, where emergency vehicles are currently sited to allow prompt access.

While the Scottish Government is committed to dualling the A9, everyone should understand that this is not merely a case of building a parallel carriageway where required. We are looking at a project which may well run for decades and defy budget projections. If so, that will require commitment from all political parties. I'd like to hear Murdo Fraser and others say their parties are so committed. I wonder if I will.

Councillor Alan Grant, Deputy Leader, Perth and Kinross SNP Group.2 High Street, Perth

William Barlow (Letters, August 1) says that I could not be more wrong in campaigning for an increase in lorries' speed limits on safety grounds. I refer him to the Parliamentary Advisory Council for Transport Safety report of June 4, 2005, that counselled against increasing the general speed limit for cars on motorways to 80mph on the grounds that increasing the speed differential between cars and goods vehicles would be detrimental to road safety.

What the industry wants is a reduction in the speed differential which we believe will contribute to increased safety by, apart from anything else, reducing the "A9 weave" as practised by so many frustrated car drivers and which leads to so many accidents and even more near misses. If nothing else, we need some detailed research into what the effect of increasing goods vehicle limits to a more sensible 50mph would be. Coaches can travel on single carriageway roads at 50mph. What makes a coach loaded with 53 passengers more inherently safe than a goods vehicle?

Gavin Scott, Head of Policy, Scotland, Freight Transport Association, Melville Terrace, Stirling.

Brian Conner suggests I should "drive a mile in a man's truck" before I judge him. How about I drive a mile in his truck on the A9 and show how easy it is to judge the size of the queue of cars behind him. I could then use this as an opportunity to demonstrate pulling in as the simple alternative to overtaking when breaking up a convoy and letting traffic flow freely.

Peter MacDonald, Glasgow.