A new tunnel has been opened on the A3 aimed at reducing traffic jams on the congested route between London and Portsmouth.
The trunk road tunnel at Hindhead, Surrey, is the longest ever built in the UK and has taken four years to complete.
It is part of a £371 million scheme to relieve jams along the busy route.
Transport secretary Philip Hammond said it was thought the new road would improve journey times by 20 minutes or more at peak times.
Some 104 CCTV cameras have been placed throughout the tunnel, the Highways Agency said.
Southbound traffic will be the first through the tunnel, with northbound traffic introduced a few days later.
Mr Hammond said: "This is another one of the 'missing links' in Britain's trunk road network now in place.
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