Motorways did not have speed limits when they first opened
The 50th anniversary of the opening of the first stretch of motorway in the UK is being marked - by the opening of the latest bit of the M6.
In 1958, the Preston bypass was unveiled with no speed limit.
Fifty years on, the £174m M6 Carlisle to Guards Mill extension in Cumbria will mark the innovation.
This will close "the Cumberland Gap", enabling motorists to use motorways all the way between southern England and Glasgow.
AA president Edmund King said motorways were a great success story.
"Motorways are five times safer than single lane roads but the accident rate increases when motorways are congested. Motorways have transformed the way we travel."
Work on the M6 extension in Cumbria started in 2006 and the 5.8-mile, three-lane stretch of motorway replaces the A74 dual carriageway road.
Transport Minister Lord Adonis, who will open the new road later, said: "In half a century, motorways have become the backbone of the UK's road network.
"They are the lifelines of the country, making an invaluable contribution to our business and economic needs and they help keep friends and family connected."
But government plans to use the hard shoulder on motorways to manage future growth in road traffic have been criticised by the RAC Foundation as inadequate.
In a report, the motoring body said concentrating all road improvements on existing motorways through widening and hard shoulder running was problematic.
Road development should focus on developing the motorway network, it said.
The claim was rejected by a Department for Transport spokesman.
"Motorway trials have already proven that hard shoulder running cuts congestion, smoothes traffic flows and offers more predictable journeys," he said.
The spokesman added that the £6bn investment package announced earlier this year would also fund other measures, such as improvements to junctions and trunk roads, "to provide a safe, reliable and sustainable motorway network for the 21st Century".