It came in a Holyrood debate in which Highlands and Islands Conservative MSP Donald Cameron said the £15 million spent on attempts to prevent further landslips from blocking the notorious stretch of the A83 in Argyll had not worked.
He said 100,000 tonnes of debris was sitting above the road at risk of falling.
Mr Cameron said: “This is very threatening for a vast number of people.”
Highlands and Islands Labour MSP Rhoda Grant said: “What’s terrifying is the amount that’s unstable and is in danger of falling.
"I really do fear for this winter.”
Mr Dey said: “It is quite scary when you go there and see what has developed on the site, and the necessity of the work which has been done by the engineers.”
Mr Cameron said the estimated seven to ten years needed to build a replacement for the current A83 along the other side of Glen Croe must be shortened.
He said: “The short-term fixes that have been applied to attempt to make it safer and reliable simply have not worked.”
This has included a series of “catch pits” and heavy-duty fencing constructed beside the road to try to stop landslides reaching the carriageway.
Mr Cameron said: “There is a broad acknowledgement that in the event of some of the worst landslips that we have seen, even these mitigation measures simply won’t prevent the road from closing.”
He also called for faster short-term measures, such as upgrading a forestry track as an alternative route because the current emergency diversion route on the Old Military Road below the A83 had also been closed in some landslides.
The MSP said residents could not wait ten years, with businesses suffering hugely when the road was shut.
He said dairy farms transporting milk were “massively affected” by the lengthy detour involved and Argyll bus operator West Coast Motors had increased its mileage by 175,000 a year.
Highlands and Islands MSP Jenni Minto, who described the A83 as a “strategic lifeline route”, said the two-and-a-half hour journey between Tarbert and Glasgow was increased by two and half times if drivers had to take an alternative route involving ferries.
Mr Dey said the Rest and Be Thankful was “one of the biggest engineering challenges in Scotland” because of its location.
However, he said the correct statutory processes for a new road must be followed to avoid the risk of a legal challenge delaying the project if “someone picks a hole in the process followed”.
The minister said a “resilient route”, which could be based on the Old Military Road or forestry track, would be built ahead of the new road.
However, he said it must be based on sound engineering and there was evidence of landslides on the other side of the glen too.
The precise route of the replacement A83 has yet to be determined and could include viaducts and tunnels, at an estimated cost of between £268m and £860m.