The works at Pulpit Rock will remove a notorious bottleneck at Loch Lomond, getting rid of traffic lights which have been there for 30 years.
The improvements include a new 400m section of two-lane carriageway, a viaduct running parallel to the loch shore for 180m and the widening of the existing carriageway.
Construction is expected to last a year and cost £12m. As the road is wedged between Loch Lomond and steep hillside, the works provide “real engineering challenges”.