The closure of the M74 near Glasgow next month could be followed by traffic also being diverted off the nearby A8 for several weeks next year.
The roadworks could cause drivers the biggest headache yet during the £500 million upgrade of the M8/M73/M74, which is already causing daily misery for commuters.
The Scottish Government’s Transport Scotland agency (TS), which is in charge of the project, confirmed it is planning to close a three-mile stretch of the M74 from Friday 18 to Monday 21 November.
In the first closure of its kind for decades, the motorway would be shut between junction four with the M73 at Maryville and junction five at the Raith interchange.
The three-mile stretch, used by 70,000 vehicles a day at weekends, will be closed for the demolition of Bothwellpark bridge over the motorway north of Raith, which has been replaced by a new bridge.
TS said options were also being considered for major roadworks on the A8 at Baillieston in late February.
The dual carriageway, used by 100,000 vehicles on weekdays, is being replaced with a new section of the M8.
An industry source said options included diverting A8 traffic via a new A89 link and through a roundabout for up to nine weeks.
TS said the motorways upgrade completion remained on time for the spring. But one source said: “It will get to a stage in the next few months where they will be forced to admit it is behind schedule.”
TS said the impact of the M74 closure was expected to be “significant” because of the number of people heading to Glasgow for Christmas shopping and other events.
A spokesman said: “As part of the M8 M73 M74 Motorway Improvement project (MIP), TS and its contractor, Scottish Roads Partnership, is in discussions with a stakeholder group regarding a proposed weekend closure of the M74.
“Current plans indicate the preferred date for the closure is likely to be Friday 18 November at 8pm to Monday 21 November at 6am.”
South Lanarkshire Council transportation chief Gordon Mackay said the closure would cause “significant congestion and inconvenience”.
Neil Greig, of the IAM RoadSmart motoring group, said: “These improvements are very important but their long-awaited arrival is certainly trying the patience of long suffering M8 and M74 users.
“There are very few alternatives to full closure when safe bridge demolition is required.
“As ever, the key to keeping traffic moving will be good advance information and swift response to incidents and breakdowns.”
On the A8 plans, TS said it was considering, with other affected organisations, “a number of traffic management options” to facilitate the opening of the MIP in spring 2017”.