The stark warning came after public spending watchdogs highlighted a three-year reduction in repairs funding.
It came in response to former infrastructure secretary Alex Neil asking at the public audit committee whether continued spending cuts risked a “crisis point”.
Hugh Gillies, director of roads for Scottish Government agency Transport Scotland, said: “Can we continue the way we are going as a country? No we cannot.
“Scotland’s roads need investment. Can it carry on as it is without something significant happening down the line? No.”
Audit Scotland reported last August that Transport Scotland had cut spending on motorways and trunk roads by 4 per cent between 2011-12 and 2014-15.
Councils reduced their spending on other roads by 14 per cent over the same period.
Liz Ditchburn, the Scottish Government’s director general for the economy, told the committee that trunk road maintenance had increased by £15 million in 2016-17.
She said the Scottish Government’s draft budget for 2016-17 included spending on trunk road maintenance, operation and management increasing from £305m to £368m.
However, she said more spending would be required on Scotland’s motorways in the future because of their age.
She said: “If you have got a 40-year-old motorway, there is a point at which you have to face where there is no longer just a patching option and you need to go for a more significant investment in renewal.
“Those are the sort of decisions which mean you may be looking at big numbers on maintenance.”
Transport Scotland chief executive Roy Brannen said trunk roads were in a “reasonable” condition.
He said their deterioration was slowing down but there had been “certainly no significant improvement”.