Hopes are high that the tunnel which will cut traffic congestion at the Raith Interchange could open as early as next week.
Work on the 560-metre underpass — one of the key elements in the M8 M73 M74 Motorways Improvement Project — is believed to be in the final stages.
When complete, it will allow drivers travelling on the A725 between Bellshill and East Kilbride to avoid the bottleneck Raith roundabout at junction 5 of the M74.
Work at Raith began more than two years ago. Construction of the tunnel has required excavation to a depth of 10 metres with a complex drainage system installed to prevent flooding from the River Clyde.
Huge amounts of concrete have been poured in to form a one-metre base. This has been done in instalments, the last of which was at the weekend.
A source involved in the work said: “All that is required now is a waterproof seal and then the road surface can be put down. We’ve been told February 1 is the target date for the tunnel opening.”
Transport Scotland has always insisted the entire motorways project is on schedule for completion this spring, but refused to say if individual sections could be ready earlier.
Central Scotland MSP Margaret Mitchell, who has been critical of the contractors for disruption caused to nearby residents, welcomed the prospect of the tunnel opening soon.
She said: “If this is imminent it is excellent news. Not only will the tunnel help drivers on the A725, it will have a knock-on effect for motorway traffic.
“We’ve all understood the work had to be done, but it’s caused massive inconvenience and this finally is great news for all who have shown such patience.”
Transport Scotland refused to comment on a possible opening date. A spokesman said: “We are working closely with the contractor, Scottish Roads Partnership, to open completed sections of roads as they become available to help alleviate congestion.
“Work at Raith Interchange is progressing well and drivers will be notified in advance of any change to traffic management layouts.
“We thank road users and local communities for their on-going support and patience during these necessary works.”