Easter traffic is expected to peak later today at the start of a four-day holiday period that will see 20 million car journeys.
About 6.6 million Britons are planning a trip involving an overnight stay over the weekend, according to tourism body Visit England. That is up from six million last year.
The worst time to travel on the roads is expected to be between 4pm and 6pm today, when traffic will be about 28% above the average for those hours, according to Inrix, which provides traffic information.
On major motorways, some journeys could take three times longer than usual, the group said.
Highways England has told drivers to consider alternative routes and allow extra time for their journeys.
Motorists driving between junctions 9 and 21 on the M25 should expect delays of up to 90 minutes, while those heading in both directions on the M6 and southbound on the M5 towards the West Country could have delays of an hour.
By contrast, Easter Sunday will be the quietest day of the period, with 25% less traffic compared to an average Sunday.