SCOTLAND is facing a bill of nearly GBP2bn to shore up its crumbling road network, the nation's spending watchdog has warned.

Audit Scotland said councils alone would have to invest GBP1.5bn to bring their roads up to standard after a decade of relentless rises in traffic volume. A further GBP325m was needed to fix trunk roads.

The agency, in a report published today, gave the Scottish Executive a gentle pat on the back for its efforts to boost transport. Overall spending hit GBP1.5bn last year and is expected to rise to GBP2.3bn in 20072008.

Investment rose fastest in public transport, with huge rises in bus and rail travel and a free bus-pass scheme that has proved so popular that nearly a million people have signed up for it - prompting concerns over its future viability.

Spending on roads, however, has risen much more slowly.

Councils, Audit Scotland said, spent less on their 31,700 miles of roads in 2003-04 than they had in 1995-96. However, traffic has leapt nearly one-fifth in the same period.

The report said: "Overall around 40per cent of all local roads and one-third of local authority A roads may require some form of maintenance or further investigation to establish if further treatment is required."

Scotland's 2200 miles of trunk roads were in a better state. The responsibility of the Scottish Executive, they get more than 10 times as much funding per mile as local roads. Still, more than one-fifth of trunk roads have a "residual" lifespan of less than five years.

A spokeswoman for Transport Scotland, the body responsible for trunk roads, said: "We have identified work which is required to be done to the trunk road which amounts to GBP325m.

"This does not include anything that requires urgent attention and the value amounts to just 2.5per cent of the entire trunk road asset value of GBP12bn. We will take forward all work in future repairs programmes."

Councils - and especially their road officials - have long complained of low transport funding.

A spokesman for Cosla, the body that represents local governments, said: "We have consistently recognised this as a priority and will no doubt continue to press the executive for increased funding."

The executive said its payments to councils for transport had risen every year since 1999 - but stressed that it was up to local authorities to spend their money as they saw fit. The overall backlog of repairs for council roads has officially fallen from GBP1.7bn in 2004 after a recent funding boost.

However, one senior Scots roads official said the real figure for the maintenance backlog on council roads would far exceed GBP2bn.

Audit Scotland, meanwhile, also cast doubts on whether the executive would meet its target of at least holding congestion levels at 2001 levels for 20 years.

The latest forecast is for traffic to grow by more than a further quarter by 2021. Congestion on trunk roads is costing the economy GBP71m a year.

Neil Greig of AA Scotland believes Audit Scotland should have been tougher. "There is a crisis in the funding of local government roads, " he said.