Speed limits are set to be slashed on part of the A47 which has seen a string of fatal crashes.
Highways officials have confirmed a £3m package of safety measures east of the Hardwick Roundabout, on the outskirts of King's Lynn.
They include extending the 40mph limit at Constitution Hill, where three people died in January.
Paul Carter, his wife Lisa Carter, who were both in their 40s and Mrs Carter's daughter Jade Mace, who was in her 20s lost their lives after their Vauxhall Mokka was involved in a head-on collision with BMW X5.
Aurelijus Cielevicius, 39, from King's Lynn, has been charged with three counts of causing death by dangerous driving, in connection with the collision.
The crash brought the death toll on that stretch of the road to five in as many years.
A man in his 70s died in a crash involving two BMW cars on the Hardwick Roundabout on April 5.
Measures in the pipeline also include reducing the limit from 60mph to 50mph between North Runcton and Middleton, reducing the limit in Middleton from 40mph to 30mph and reducing the limit at West Bilney from 60 to 50mph.
National Highways said the changes have come from "detailed research of the road over a number of years" and are "not a direct consequence of recent collisions".
It added: "Safety is a priority and we regularly review all our roads, including detailed analysis of casualty data. This helps us to prioritise where safety improvements can be made.
"To reduce the number of high severity casualties on the section of the A47 between the Hardwick Roundabout and Pentney a range of safety measures have been designed."
There will also be new road markings to ban overtaking on some stretches, improvements to junctions and speed warning signs.
The date when the new measures will come into force has not yet been announced.
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