A landslide caused by Storm Darragh means what was a six-mile trip is now 25 miles.
The A487 has been shut between Corris and Minffordd, Gwynedd, since Wednesday because of worries about unstable ground above the road.
The Welsh government said it hoped to resolve the matter quickly but there are fears it could be closed for months.
Builder Martin Jones, who was driving to Dolgellau just after the landslide, caused by Storm Darragh on Saturday, said: “If I was 10 minutes earlier, I could have been caught up in the landslide and, you know, I’d have been stuck or maybe worse.”
Mr Jones, from Aberllefenni said the closure was an inconvenience as his young daughter goes to a nursery in Brithdir and a journey “that normally takes quarter of an hour” is now 45 minutes each way.
Martin JonesDennis Jones, from Corris, was shocked by the landslide’s scale.
He said: “The volume of land, mud and trees that has come down is unbelievable. Luckily, they were cleared very, very quickly by a local contractor.
“But since then, they’ve done a survey of the actual land that’s left on the slope, and apparently that is very, very dangerous and is still unstable.”
He said there was little information about when the road would reopen, adding: “Some have said a few days, others have said 10 to 15 days. But somebody this morning said it could be up to two or three months.”
The Welsh government said the road was closed for safety reasons and the North and Mid Wales Trunk Road Agent was trying to fix the road “as soon as possible”.
