Fuel-price protesters are driving slowly along the M5 and A38 as part of demonstrations during the busy summer getaway period.
More disruption is expected later, including along the M4, from slow-moving convoys by drivers calling for action to cut the soaring cost of petrol.
In a similar protest earlier this month, around a dozen people were arrested for driving too slowly.
Demonstrations are believed to be planned nationwide, including in Birmingham, Cardiff, Liverpool, London and Manchester, according to information on the Facebook group for Fuel Price Stand Against Tax.
Avon and Somerset Police warned motorists of “slow-moving roadblocks” on parts of the M4, M5, M32 and A38 on Friday morning.
The force said the M5 and A38 action began at around 9.30am.
The demonstrations are expected to cause disruption on an extra-busy day for roads when schools have been breaking up for summer holidays.
