Roadworks on the A35 due to restart next week could delay commuters up to an hour.
Dorset County Council has warned people to choose a different route if they intend to travel westbound on the A35 on the Upton Bypass.
The work to repair the Policeman Lanes Bridge will start on January 14 - and is due to last for five weeks, with the inside lane closed to traffic.
A spokesperson for Dorset County Council said: "Drivers are advised to change their travel plans, or there is a risk of tail-backs for several miles and delays of up to an hour.
"The lane closure will allow work to strengthen the bridge support columns and carry out surfacing work, barrier repairs, drain cleaning and verge clearance."
Drivers are advised to instead travel on the A349 Gravel Hill up to the Merley Roundabout and onto the A31.
The work will move to the central reservation from February 18 - affecting both west and eastbound traffic with lane closures in both directions.
Cllr Peter Finney, Dorset County cabinet member for highways and transportation said: "Many drivers tend to commute on 'auto-pilot', so we're giving plenty of advance warning of this work to ensure that drivers can take action to avoid these delays from day one.
"We are carrying out this work at a time of year when the daily average number of cars using the road is at its lowest, but we know it will still have a large impact on people's daily journeys.
"Drivers should try to understand that this work is for their benefit - the road needs to be maintained so that it can continue to be used by thousands of vehicles that use it every day."