Drivers in Preston are being warned to expect delays while major work takes place on Ringway, the dual carriageway through the city centre.
Workmen will be applying a protective waterproof layer to the underpass near the Market Street car park to prevent the bridge being damaged by water.
The work is planned so disruption to traffic will largely be limited to evenings and three weekends - starting this weekennd - to avoid delays to peak time journeys.
On weekdays work will take place overnight from 8pm to 6am with lane restrictions in place.
At the weekends of Friday May 29 to Monday June 1, Friday 5 June to Monday 8 June, and Friday 19 June to Monday 22 June, highways teams will work continuously through the day and night.
During these weekends, traffic will be able to use Ringway, but at times only one side of the carriageway between North Road and Friargate will be in use, with traffic management in place and both directions reduced to one lane.
Ridwan Musa, Lancashire County Council highways manager for Preston, said: “We’re sorry for the disruption this work will cause, but it’s essential that we carry out maintenance to waterproof the underpass to preserve the bridge and prevent more inconvenience and cost in future.
“We’re planning to minimise inconvenience to people’s journeys as far as we possibly can by working overnight and at weekends, when traffic is lighter.
“We’re aware that the weekend work in particular has the potential to cause some disruption, and we’re advising people to use alternative routes if they can.
“We’ll be working 24-hours per day over these weekends as some aspects of the project mean that we need to work continuously and it will cause less disruption to do this work at the weekend than during the week.
“We’ve scheduled the work for these dates but the waterproofing work is weather-dependent. We’ll therefore do our best to let people know if things change through the media, the county council’s website and social media channels.”