A council in Somerset has warned hauliers a temporary weight restriction has been implemented across the A36 Cleveland Bridge and heavy goods vehicles cannot use it.
The restriction is being put in place ahead of essential structural repairs to the Grade II listed structure which are being planned for later in the year.
Surveys show some structural parts of the bridge have come to the end of their life and the weight restriction is being introduced as a precautionary measure.
Signed diversion routes, using designated roads suitable for large vehicles will be in place for through traffic while those vehicles needing to go into Bath city centre will be directed to the city from the west using the A4.
The distance on the diversion from Bath to Warminster is 25 miles; the normal distance using the A36 is 17 miles.
The diversion would add eight miles to journeys for traffic heading to the south.
Councillor Neil Butters, joint cabinet member at Bath & North East Somerset Council said: “The weight restriction is being taken as a prudent measure until we have completed the necessary repairs to the bridge.
“We have a very extensively signed diversion route for heavy vehicles which has been drawn up with our neighbouring authorities and we are asking operators of HGVs to use this route and not follow unsuitable roads.”
The bridge was originally constructed in 1826 for horse drawn vehicles and pedestrians, now carries 17,000 vehicles a day including more than 600 HGVs.