Transport Scotland, which oversees the 2115-mile network of motorways and primary A-roads, has told The Herald there is a maintenance backlog of £755m, up 6% on last year, when a national summit was ordered to address the declining state of Scotland's roads.
A separate examination of the condition of carriageway surfaces has found 79% of trunk roads are now in an acceptable condition while the remaining 21% require attention.
The figure has remained stable over the last two years but is significantly higher than in 2006, when only 16% of the trunk road network was deemed to be in an unacceptable condition. More than one-third of local authority-owned roads are deemed to be in an unacceptable condition, according to a similar survey published earlier this year.
The maintenance figures, disclosed under freedom of information rules, shed new light on the condition of Scotland's major arterial routes, which carry 37% of the country's traffic.
However, the Government agency has refused a request to publish its Road Asset Management Plan (Ramp), a document intended to let motorists know what it is doing to maintain trunk roads. The last Ramp, covering a two-year period, was made public in 2007 but publication of updated versions has been repeatedly deferred over the last two years amid uncertainty about how much money would be made avail- able by ministers, Transport Scotland officials said.
A breakdown of the maintenance backlog shows the £42m increase in costs is entirely down to bridge repairs. Donald Morrison, head of asset management at Transport Scotland's roads division, said this was a result of new defects being identified, rather than a decline in the overall state of the network.
Mr Morrison also pointed to separate figures that show the proportion of "life expired" routes in the trunk road network had remained stable since 2007. This is based on surveys of how well the road's foundations responded to the weight of vehicles rather than examining defects in the surface, he said.
Professor Stephen Glaister, director of the RAC Foundation, said: "The good news is that Transport Scotland are transparent about the state of the nation's roads. The bad news is that they still haven't published an asset management plan to look after them."
A spokesman for the Automobile Association added: "A Scottish road maintenance review has been carried out and the Government knows what it has to do to keep pace and arrest any decline."