A 47-mile (76km) diversion route has been set up by a council.
A stretch of Church Street in Highbridge is to shut for road works on weekday evenings for eight days, starting on Monday.
Somerset County Council says lorries cannot be sent down narrow rural roads with weak bridges.
The authority does not believe anyone will actually use the formal diversion, the spokesman added.
The resurfacing work will avoid peak times and weekends.
The diversion would see drivers pass through places including Pawlett, Glastonbury, Wells and Axbridge.
The council spokesman said the authority was legally required to divert on like-for-like roads - an A road for an A road, B road for a B road.
He added that local people would probably find their own solutions, and that it expected lorry drivers and those with sat-navs to use the M5.
"We're putting up signs for local people to use the industrial estate, as well as signs for heavy traffic to use the motorway," the spokesman said.
"We don't believe anyone will use the formal 47-mile round trip but legally we need to have this in place."