Local councils in Wales have called for more than £20m in extra funding to begin a programme of road improvements.
A report to the Welsh Local Government Association (WLGA) admits road repairs have been neglected in recent years.
The report says that much of the extra money that authorities had received from the Welsh Assembly Government has been spent on other areas.
An assembly government spokesperson said it was waiting to receive the final report.
A report carried out by the Institute of Civil Engineers (ICE) in 2003, said that more than £1bn is needed to clear the backlog of repairs on rural and urban roads across Wales.
Rural and urban roads in Wales are in a worse condition than those in England or Scotland, according to the survey, with the most severe problems are on roads maintained by councils.
And the WLGA said the current situation was "unsustainable" and that the continuing deterioration of roads was making repairs more expensive.
There has been a gradual deterioration in the highways
The association said it would urge the assembly government to find an extra £20m, which it said would only be the beginning of a programme of investment.
According to the WLGA, extra money that Wales' 22 local authorities has received from the assembly government has been used to meet the increasing cost of teachers and growing numbers of people using social services.
In a statement, an assembly government spokesperson said: "We are yet to receive the final report of the expenditure sub group, which will then be considered by the local government minister (Sue Essex)."
Over the last three years, the assembly government has made £247m available in transport grants to local authorities.
Of this, £149m has been drawn down, leaving approximately £100m unspent. This money has remained with the assembly government.
Dennis Morgan from ICE said massive investment is vital for road improvements.
"Over the last 20 years there has been a gradual deterioration of the stock of highways throughout the nation and we are at a point now where a fairly massive investment is required to bring the network back up to the state where annual maintenance expenditure will keep on top of the job," he told BBC Wales.
"I don't think we can blame current policy makers in anyway - we are dealing with a 20 year backlog of successive under-investment in our highway system.
"It's not something that has happened overnight, it is a gradual process that has built up and is now at the point where we require these large sums of money to solve the problem.
"Traffic has dramatically increased over the last 20 years and this is putting greater and greater strain on the road system.
"The life of a road is directly proportional to the use it gets and when maintenance expenditure over this period of time has been under the levels it should have been, we get these cumulative problems that we now need a lot of money to get things back to normal."
He said that additional expenditure for the roads needs to be made every year for the next 10 years in order to bring the roads back to standard.