More work is being done on the Highway 1 Kicking Horse Canyon project east of Golden.
The fourth and final phase will cost in the neighbourhood of $601 million dollars.
The upgrades will improve safety and traffic flow while helping businesses move their goods.
Work includes realigning and widening the final 4.8 kilometres through the canyon to four lanes and installing median barrier, snow avalanche and rock fall hazard protection.
Construction is expected to start next summer with extended highway closures, at times.