Drivers have been warned that work on the Norwich Northern Distributor Road will mean Fakenham Road will have to be shut for four nights next week.

The overnight closures are necessary because of work to tie in existing road to new roundabouts on the 12.5 mile route, which will stretch from the A47 at Postwick in the east of the city to the A1067 Fakenham Road.

Fir Covert Road had been due to close last night, but the wet weather forced that to be delayed until Monday.

It is due to shut at 8pm that night and reopen by 6am on Tuesday. It is then due to close again on Friday, September 30, with traffic diverted via Drayton High Road, Boundary Road and Reepham Road.

And to connect the A1067 Fakenham Road to the new roundabout, that road will shut overnight between 8pm and 6am for four nights – from Tuesday until Friday.

Light vehicles will be diverted (north to south) via the B1145 through Reepham, Reepham Road and Fir Covert Road.

And HGVs will be diverted (north to south) via the B1535 Weston Hall Road to the Wood Lane junction with the A47, then into Norwich, using Sweet Briar Road (Norwich ring road) to return to Drayton High Road (A1067).

Once complete, A1067 traffic will be moved on to the realigned section and the old road will be broken up, with the material re-used on the NDR. John Birchall, Norfolk County Council's NDR community liaison officer, said: 'If carried out under the NDR project's normal 7am to 7pm working hours without road closures, the work on these two roundabout tie-ins would take several weeks and have an extended impact upon traffic.

'Working alongside traffic under lane closures would also lead to multiple joints in the road surface, reducing durability, and would have safety implications for construction workers and road users.'

Overnight working is already under way at Rackheath, where pilings for a new bridge are being put in place. The work is having to be done at night because Network Rail would not allow work in hours when trains were running on nearby tracks.

The county council's environment, transport and development committee yesterday heard that the estimated cost of the road, budgeted at just under £180m could rise by £6.8m.

The need for night working at Rackheath, potential extra costs connected to acquiring land and 'unseasonal rainfall' during June have been blamed for the possible increase, which has led to the project being rated as an amber risk under the council's risk rating system.