Motorists face major delays and disruption as maintenance roadworks get under way on the A31 in Dorset.
The upgrading work, near Corfe Mullen, was due to start on Monday night.
Night-time drivers face a 10mph speed limit plus 10-30 minute delays on the road - running north of Bournemouth, and south of Wimborne Minster.
During the day, there will be a temporary 40mph speed limit. But from 2000 until 0600 BST, work will continue in both directions until 5 November.