Work to replace the damaged culvert on the A458 at Spring Bank, Golfa, has been delayed and will now start on Monday, January 24.
The work was due to start last week but the Welsh Government’s Highways Agency said the project had been delayed for two weeks.
Diversion signs will be in place taking west and eastbound traffic on a 15-mile route once work to replace the Spring Bank culvert starts.
Powys county councillor for Welshpool's Llanerchyddol ward, Graham Breeze, said it was difficult to understand the delay in work starting, and the length of closure needed for the work.
He said he and fellow councillors would press to ensure the work is completed before the Easter bank holiday.
The diversion route directs westbound drivers onto the A490 for seven miles before turning left at the A495 junction to travel eight miles along the A495 to re-join the A458, with eastbound drivers following the route in reverse.