After two public inquiries and the odd government U-turn, the new stretch of dual carriageway running behind the Hilton hotel is expected to solve one of the worst traffic bottlenecks in the south east.

The 18-month project has caused massive disruption to traffic flows, and many in the daily lorry convoy from Southampton to the midlands, have preferred rat-running on the B4009, A4 to Hungerford, and B4494 to Wantage, rather than sit in jams waiting to get on to the M4.

The junction is used by 90,000 vehicles a day, but car use is predicted to increase 20% in the next 10 years in the Newbury area, and environmentalists fear that the route – which is already running at capacity – will quickly clog up.

However, a repeat of last year’s five-hour logjam on Newbury Show weekend is now unlikely for this year’s event in five weeks’ time, which will draw crowds of over 60,000.

Costain project manager Darren James said in a letter to residents: “We would like to thank you and road users for understanding our necessary traffic management arrangements since we commenced work in spring 2003.”

The northbound stretch of the three mile road will open at 11am, with the southbound switch coming overnight. There will be a temporary 40 mile an hour limit, and transport minister David Jamieson is expected at the opening ceremony.