National Highways (NH) has released full details of road closures needed to begin preparation work for the A417 missing link – with the first no-go beginning tonight.

The £500m-budgeted scheme, most recently estimated to come in at £460m, should begin in earnest this autumn. The aim, says NH, is to deliver "a safe and resilient free-flowing road while conserving and enhancing the special character of the Cotswolds Area of Outstanding Natural Beauty."

The improvement will spell the end for the ill-fated single-carriageway pinch point by connecting existing dual-carriageway sections of the A417 at Brockworth and Cowley. Work is scheduled to be completed by early 2027.

An NH spokesman said: "There's lots of work that needs to be done before construction begins in the autumn. If you're in the area, you will start to see some local public rights of ways being diverted and people out on site undertaking archaeological digs and installing environmental mitigation such as animal fencing and bat boxes to protect local wildlife.  Later in the year, you will also start seeing people setting up construction site offices and protecting nearby utilities so they are not impacted by the build."

Project director Michael Goddard told Radio Gloucestershire: "One of the questions we always get is how can it cost so much money, £460 million for a relatively short road. And that's because of the complexity of the area. Climbing the escarpment, the environmental work we need to do, so in terms of national highways it's one of our bigger projects."

The 3.1-mile stretch of single-carriageway road to be improved was opened as a bypass for the village of Birdlip in 1988 and the project cost £2.4m. Based on estimates, the replacement infrastructure will now command a price tag of £148m per mile.

Initial work tonight and for four nights will see full closure of Crickley Hill from the A46 to the Air Balloon Roundabout, sessions finishing at 6am. Full details of this and subsequent diversions can be viewed here . There will also be overnight closure at the Cowley end of the A417 scheme on Thursday.

Last April, construction giant Kier Highways was awarded the £460m contract for the work by NH, and the contract followed a competitive procurement process through National Highways' Regional Delivery Partnership framework.