The diversion around the landslide at the Rest and Be Thankful on the A83 remains in place today while the clear-up operation continues.
And further heavy rain is forecast for early evening and overnight.
The busy Tarbet to Campbeltown trunk road was closed Tuesday morning after thousands of tones of mud and rocks were washed onto the carriageway in the biggest landslide that has occurred in the area.
But trunk road contractors Bear Scotland opened up the Old Military Road (OMR) as a diversion during the afternoon and it has remained in place since.
A decision about when the road will reopen fully to the public will be taken tomorrow and will be dependent on expected weather conditions.
Head of network maintenance at Transport Scotland, Graham Edmond, said: “The Old Military Road operated successfully again overnight with no issues to report.
“It continues to prove its worth as a back-up option, drastically cutting the diversion route and helping to support the message that the area remains open for business.
“I would again like to put on record my thanks for the patience and understanding shown by the local community and motorists affected, most of whom will appreciate that their safety is paramount.
“With heavy rain forecast later today the OMR remains in use, although inspection teams will be out first thing tomorrow to confirm when the main road can reopen safely.”