The limit has been introduced on the A189 Spine Road in Blyth to slow traffic northbound between Three Horse Shoes and Bebside roundabout.
The restriction, which will remain in place until the end of September, was requested by Northumberland County Council for safety reasons while utility works are carried out in the area.
The 3,000 metre stretch of road has been reduced from a 70mph limit to a 50mph limit, and then 40mph, with the restrictions stated on roadside signs.
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However, Northumbria Police have been made aware of a number of reported collisions and near-misses in the area, with officers identifying speed as an aggravating factor.
Officers have now appealed to the public to heed their warning and slow down – or risk potentially catastrophic consequences.
Sergeant Glen Robson, of Northumbria Police’s Operation Dragoon team, said: “We are committed to making sure our roads are as safe as possible for all road users, and clearly that relies on the public working with us.
“In this particular area, a temporary speed limit has been introduced by the local authority – but we have been made aware of a number of motorists who have simply been driving too fast.
“We are continuing to monitor the road with the council and, should motorists continue to drive too fast, we may be required to assess enforcement options.
“I’m today appealing to everyone to slow down and take extra caution. Any death or injury on our roads is always a tragedy, and we know that speed can be a contributing factor in such incidents.
“By flouting the limit, you are potentially putting lives in danger – so please be vigilant and stick to the limit. By working together, we can ensure our roads remain as safe as they possibly can be for all."
Anybody with dashcam footage showing somebody driving dangerously or carelessly can upload it directly to our website. Visit https://northumbria.police.uk/our-services/report-it/dashcam-submission/ for more information.
Meanwhile, the A193 Links Road in Seaton Sluice will be monitored by Northumberland County Council after a petition was presented to councillors.