Lowood Bridge, near Tweedbank, is to be closed for five months for repairs starting at the end of the month.
The grade B-listed bridge will be closed to all traffic and pedestrians from Wednesday, January 31, for around 20 weeks to allow the £640,000 works to be carried out.
Those repairs are scheduled for completion in June and, once finished, the 26-tonne weight limit currently in place on the 250-year-old crossing, between Galashiels and Melrose on the B6374 road, will be lifted.
Improvements to the Galafoot Bridge on the A6091 road by trunk road operator Amey will be carried out later in the year to avoid the disruption to motorists that a clash with the Lowood Bridge works would cause.
Diversions signs will be put up, the alternative route being via the A6091, A7 through Galashiels and the B6374 road.
Pedestrians can use the Chain Bridge at Gattonside to get over the River Tweed.
Scottish Borders Council’s executive member for roads and infrastructure, Selkirkshire councillor Gordon Edgar, said: “We appreciate that the closure of Lowood Bridge will have a significant impact, but once these essential works are completed, weight restrictions will be removed and the bridge can once again be used by all vehicles and pedestrians.
“We would ask local people and commuters to give themselves a bit extra time for their journeys during the repair and strengthening works to the bridge, which will ensure this vital transport link can be used for many years to come.”
The works are part of a programme of bridge repairs also including improvements to Clackmae Bridge, near Earlston; Bowanhill Bridge, near Teviothead; and Bowden Church Bridge, between Midlem and Newtown.
Several bus services will run along different bus routes during the closure, and a temporary bus stop will be added at Winston Road in Galashiels.
The No 60 service from Galashiels at 5.15am, 6.15am, 7.37am and 8am on weekdays and 6.30am on Saturdays will operate via Langlee, Winston Road, Tweed Road and Kingsknowes Roundabout heading to the A6091 and the Borders General Hospital at Melrose, and its 8am run from Galashiels will leave five minutes earlier on schooldays, at 7.55am.
The No 67’s 7am service will also leave Galashiels five minutes earlier, at 6.55am.
All other 60 and 67 departures from Galashiels will operate direct from the transport interchange via Abbotsford Road, Kingsknowes Roundabout and Tweedbank Industrial Estate.
Services 60, 67 and 68 from Melrose to Galashiels will operate direct from the hospital to Kingsknowes Roundabout, Abbotsford Road and Currie Road to the transport interchange. Buses will call at Tweedbank Industrial Estate on request.
Service 61 will go via Tweedbank and Langlee en route for Galashiels on request.
Service 71 will run from Melrose Gait via Winston Road, Tweed Road and Kingsknowes Roundabout in both directions all day.
Service 313 will operate from the hospital to Kingsknowes Roundabout, Tweed Road and Winston Road heading to Galashiels.
Earlston High School’s E01 bus will serve Darnick before calling at Gattonside both morning and afternoon.