Drivers wishing to reach the A358 for Taunton or Ilminster are diverted south at Curry Rivel, through the back roads to Hambridge and Puckington, and rejoin the A358 west of Ilton.
People wishing to access Langport from the Taunton side are directed in the opposite direction, adding up to 30 minutes and 16 miles to their journey.
The section road between Wrantage and Fivehead, known locally as Mile Hill, has been susceptible to flooding in recent times with surface water on the carriageway during times of bad weather.
Work started on 31st July 2017, with teams laying around 300 m of new pipes and building new drains and gullies to help the water drain away faster. The road will also be resurfaced at a later date to be confirmed.