A council report has revealed that many routes are now beyond the "end of their useful life."
Investment has fallen from a resurfacing rate of one in every 60 years in 1990 to a new rate equivalent to only one in 300 years.
In the report, council engineer Angus Plumb states: "The amount of money spent on roads maintenance has been declining.
The conclusion from this is that roads maintenance has been significantly underfunded for at least the last 20 years.
"The recent two winters have shown how much of our road surfaces are at or beyond the end of their useful life. In many parts they are no longer able to stand up to the use, weather, and disturbance from utilities operations."
Councillor Kate Dean, the convener of the enterprise, planning and infrastructure committee, said she accepted that the roads were in need of more investment than the council could provide.