Work to upgrade the 10-mile long steel safety barrier into a concrete one started on Monday, beginning with the installation of narrow lanes.
Central reservation work will begin once each phase is completed.
Concrete barriers are stronger than their metal equivalents, and last twice as long once constructed.
Millat Ahmed who is overseeing the upgrades for National Highways, said: ‘Concrete safety barriers significantly reduce the risk of vehicles crossing over from one carriageway to another, improving safety and reducing the duration of incident-related congestion.
‘This is an important safety upgrade and is a huge benefit to road users.’
Three lanes will remain open during the works, with the hard shoulder acting as a running lane.
A reduced speed limit of 50mph will be in place.