The emergency diversion will be used when the landslide-plagued A83 between Argyll and the Central Belt is closed, cutting more than an hour off journey times.
Transport Minister Keith Brown had estimated it would have been completed three months earlier, but the Scottish Government, local council and local businesses are delighted there is now an alternative to this vital artery road.
A convoy system will work on the 2.36 miles of single track road if the A83 is closed by landslides, as has happened six times in five years, saving motorists a 50-mile detour by Crianlarich or going by the Gourock/Dunoon ferry.
Mr Brown said: "Despite the challenges brought by bouts of severe weather, I'm delighted to see work here on the emergency road nearing completion. Our focus remains to ensure that as far as is practicably possible, Argyll stays open for business.
"To this end, the team on the ground has worked seven days a week to overcome the significant engineering challenges needed to bring the Old Military Road up to the standard needed. Subject to weather or other unforeseen events, we expect the road to be completed and available for use as early as this week."
He said the latest phases of work, costing some £750,000, to provide landslip mitigation measures at key risk points along the hillside, should be completed next month. "In addition, the feasibility study looking at more permanent solutions to landslides in the area has been put to stakeholders for their views and its findings are due to be published shortly.
Lead councillor for environment, development and infrastructure at Argyll and Bute Council, John Semple, said: "Argyll is open for business and no longer should our businesses be involved in lengthy diversions."
Mr Brown also said ministers had opened discussions aimed at helping the concil develop a business case for trunking the A83 in Kintyre between Campbeltown and the ferry terminal for Islay at Kennacraig.