A portion of the A602 between Ware and Stevenage will be shut for two days later this month.
Hertfordshire County Council is closing the road both ways between Whempstead Road and the Anchor Lane roundabout from 6.30am on Saturday, April 30 until 5am on Monday, May 2.
The council said a signposted diversion will be in place in the Watton-at-Stone, Tonwell and Sacombe areas.
Roadworks to improve safety and journey times on the A602 began in June 2020.
A Hertfordshire County Council statement reads: "The A602 is a very busy road, but there are problems in places.
"Vehicles turning right are blocking traffic behind, causing delays.
"Tight bends and poor visibility make the road less safe than it could be.
"There are often long queues at junctions.
"We want to improve the major junctions, reduce delays and make the route safer."
The finished road is set to include a larger A119/A602 roundabout at Watton-at-Stone, new cycle tracks and bridleways, and new right-hand turn lanes to reduce queues.
For the most up-to-date information about the county's roads, visit our LIVE Hertfordshire traffic map.
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Do you have a live or breaking news story from across Hertfordshire? Email: hertslivenews@archant.co.uk
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