Network Rail has announced that lanes on the A666 into Bolton will be temporarily closed while engineers undertake works below the carriageway to enlarge the Farnworth tunnel.
The lane closures, taking effect from 3 October, are a precautionary measure to ensure the project progresses without incident.
Since August additional ground condition tests have been carried out underneath the road. Although the results have not shown any cause for concern, Network Rail said it is preparing for all possible outcomes.
Nick Spall, route delivery director for Network Rail, said: “Safety is our top priority. While we expect to be able to move our tunnelling machine without incident underneath the A666, we are leaving nothing to chance.
“That’s why, as a safety precaution, lane closures are prudent while we tunnel underneath.”