A total of £240m will be spent upgrading the M1 between the M25 and Luton, the government has announced.
It will involve adding two lanes and widening the motorway to four lanes with a continuous hard shoulder.
The widening is to improve safety as well as congestion with an estimated 160,000 cars a day using this stretch through Hertfordshire.
Work is expected to start towards the end of the year and take under three years to complete.
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