While the number of cars on our roads has been growing steadily over most of the past decade, expenditure on keeping the roads in decent condition has not always kept pace.

As a series of official reports and surveys have alleged, the cost of fixing potholes, resurfacing roads and ensuring they are smooth, skid-resistant and safe to drive on has grown to the point of crisis.

An Audit Scotland report in November 2004 found that councils, which are responsible for around 32,000 miles of Scotland's non-trunk roads, were spending less on road maintenance than a decade previously - despite an 18% increase in traffic.

The Society of Chief Officers of Transportation in Scotland (Scots), which represents council transport chiefs, has since 2002 carried out an annual survey based on automatic monitoring of around 40% of the road network through a vehicle-mounted scanning machine which picks up cracks, surface erosion, bumps and potholes.

The Scottish Road Maintenance Condition Survey, which covers the 2008/9 financial year, obtained by The Herald, shows some marginal improvement, though a third of council-owned roads are still causing concern.

Working out how much this will cost is more complicated, though senior council transport officials have estimated it at between £1bn and £2bn for fixing carriageways alone. A submission to the Scottish Parliament in 2005 put the cost of addressing the backlog in roads maintenance - including carriageways, pavements, verges and lighting - at £2.5bn.

The figure is believed to now be much higher.

An added pressure is the inflation in construction costs, which have gone up by nearly a fifth since 2005, far ahead of the retail price index measure of inflation. This means that, even if the proportion of roads requiring attention stays the same, the cost for doing so will go up.

Bill Barker, the society's spokesman who is also a transport operations manager at Dumfries and Galloway Council, said Scots was compiling a detailed assessment of council expenditure on road maintenance which was due to be published before the end of the year.

This will assess whether the £249m spent in the 2003/4 financial year on road maintenance by councils has gone up or down.

As well as simply recording the locations of the problem roads, the new system being developed by Scots will for the first time include a financial modelling system that will assess where it is sensible to spend money. This will assess how much budgets will have to increase if the road network is simply maintained at current levels.

This could lead to more money being spent on "amber" category roads which require non-urgent attention.

Mr Barker said. "It's not always the best thing to treat the worst road first. Usually it's much more expensive than catching a road before it deteriorates to that stage."

Using the system at Dumfries and Galloway, which has an estimated £102m backlog in repairs, Mr Barker successfully argued for an increase in funding, calculating that its annual maintenance budget would double over the next decade if the backlog were not addressed.

Scots is hoping its report will lay the basis for a longer-term strategy that will begin to address decades of under-investment in Scotland's roads.

But there is also concern that it will be published amid the tightest spending settlement Scotland's councils have seen since devolution, when competition from other departments is likely to be keenly felt.

Stewart Turner, head of roads and amenities at Argyll & Bute Council, acknowledges this.

"I think we all recognise that there are huge demands being placed on social work and other departments and you can see the case for diverting money from roads maintenance. But the worry is that, the longer you put off improving the roads, the more expensive it will become," he said.

While A&B still has the worst record on road maintenance, Mr Turner has taken cheer that the proportion of roads requiring attention has fallen.

However, other councils displayed more mixed results. East Dunbartonshire, which has the second worst record according to the maintenance survey, has seen the proportion of roads marked "red" and requiring urgent attention increase to nearly 9%.

However, the council also recorded an overall drop in roads requiring less urgent attention - the result, its leader claims, of bringing forward capital investment of £3.5m to spend on upgrading its classified roads.

Stirling Council, which also saw the proportion of roads in the worst condition go up, also claimed to have increased its capital expenditure on road maintenance by nearly £2m over the last two years.

A spokeswoman said it has responded to the deterioration of its road network by increasing its expenditure on road maintenance for the next five years to improve the condition of the road network in line with the Scottish average and resurface 4% of the road network each year during this period."