A six-mile section of the A30 will be closed completely at the end of next week for more than two days, while a new bridge is installed.
It is part of the National Highways upgrade between Chiverton and Carland Cross.
The closure will be in place between Boxheater and the Chiverton roundabout, starting at 8pm on Friday next week, February 3.
It will then remain shut until 6am on Monday, February 6.
However, these dates are weather dependant, and in the event of very bad weather the contingency weekends have been set as February 10 to 13 and February 17 to 20 – either end of the half term week in Cornwall.
The bridge operation is weather dependent and in the event of adverse weather on the programmed weekend, contingency weekends are in place for 10-13 and 17-20 February.
Work will be carried out to replace the Tolgroggan access bridge, which has spanned the A30 near Zelah for 32 years.
National Highways said it now needs to be replaced to accommodate the realigned A30 dual carriageway between the Chiverton and Carland roundabouts.
Preparation work for the bridge replacement has been ongoing since the start of construction in 2021, and the replacement bridge - overseen by principal contractors Costain and structures specialists Keltbray - will continue to provide access for landowners either side of the A30.
The complex operation will see the new 137ft (42-metre) structure being lifted into place before the dismantling of the old bridge later in the year.
A 600-tonne crawler crane will lift the new steel twin-beam overbridge onto recently constructed foundations to the east of the old structure.
The new bridge is said to weigh 275 tonnes, which is the equivalent weight of 23 double decker buses - or 887,097 standard Cornish pasties!
Once the new bridge has been lifted into position, work will concentrate on construction of the new road.
During the road closure signed diversions will be in place via the Boxheater Junction and Chiverton Cross roundabout, with eastbound traffic diverted via the A3075 to Goonhavern and the B3285 to rejoin the A30.
The westbound diversion will operate in reverse, with the B3284 remaining open under temporary traffic signals north and south across the Chybucca roundabout.
Ahead of the weekend closure, National Highways is advising drivers to plan ahead and allow extra time for their journeys while the bridge installation is carried out.
Neil Winter, project manager for National Highways’ A30 Chiverton to Carland Cross scheme, said: “We appreciate the closure will have an effect on journey times, and we understand roadworks can be frustrating, but we are carrying out this essential work over one weekend, and when traffic levels are at their lowest, to minimise disruption.
“We’ve communicated the closure in advance to local communities and businesses and we thank drivers in advance for their patience while the work takes place.”
John Lee, project director for Costain, described it as a “key milestone for the project”, adding that as part of the scheme his team would be building 13 new structures in total - both under and over the new A30, with one existing underbridge at Two Burrows, a short distance from Tolgroggan, being refurbished.
As part of the near nine-mile upgrade, the new route will feature:
• a new junction at Carland Cross, with an underbridge linking the existing roundabout and a new roundabout to create the new junction;
• a new junction at Chiverton, formed by two new underbridges under the new A30, creating a new junction linking with the old A30, A390, A3075 and B3277 roads;
• a new junction at Chybucca formed with an overbridge;
• a ‘green bridge’ at Marazanvose, to connect wildlife habitats across the new A30;
• underpasses at Newlyn Downs, Church Lane and Chiverton for walkers, cyclists and horse riders;
• three underbridges at Pennycomequick, Trevalso Lane and Tresawen, to better connect the de-trunked A30;
• refurbishment of the existing underbridge at Two Burrows.
During the weekend closure, drivers can get travel information via the @HighwaysSWEST Twitter feed, by phoning the National Highways Information Line on 0300 123 5000 or by accessing the website: www.trafficengland.com
The cost of developing the scheme is being partly funded by an £8 million contribution from the European Regional Development Fund, with an additional £12 million for the construction phase. The remainder of the cost of developing and delivering the scheme is being funded by central Government.
The upgrade is scheduled to be open to traffic this winter.