The Old Military Road has opened on the A83 at the Rest and Be Thankful.
The temporary measure, which followed a major landslip in heavy rain on Tuesday, allows traffic to use the key route through Argyll.
Starting at 09:15 on Saturday, vehicles have been moving on the old road under a convoy system.
Engineers are continuing to work to stabilise and assess the damage on the A83 and the embankment above and below the carriageway.
Eddie Ross of road contractors Bear Scotland said: “We’re pleased to safely open the Old Military Road under 24-hour operation as a local diversion route for motorists on the A83.
“Safety remains our top priority and we will continue to closely monitor the hillside and the route to check for any issues.
“Stabilisation work continues on the A83 and will continue into next week when a timetable for reopening will be finalised.”
Mr Ross thanked road users for their “patience” while work was carried out.
He added: “Argyll remains open for business and we encourage road users to plan ahead by checking Traffic Scotland for up to date journey information.”
Updates are being issued on the Traffic Scotland website.