DRIVERS face a summer of gridlock as two major city roadwork schemes overlap.

Six months of roadworks will start next month to remodel the Heyford Hill roundabout by Sainsbury’s supermarket.

And a month later, 40 weeks of roadworks on Iffley Road will begin.

Motorists were last night warned to expect a “nightmare” summer on the routes, with a cabbies’ leader saying the work would have a knock-on effect all round Oxford’s ring road.

The Heyford Hill work is to cut two new lanes through the centre of the congested junction, widen the eastbound section of the bypass, and improve slip roads to aid traffic flow.

Temporary 30mph speed limits will be in place for more than 200 metres along all three roads leading to the roundabout, the A423, A3142 and A4074, from Monday, April 11.

The measures could be in force for up to 18 months if the project overruns.

The Iffley Road work will start on May 9, and see temporary traffic lights between The Plain and Henley Street.

The road will be closed completely between The Plain and Circus Street for up to four weeks in August. All work is expected to finish by March 2012.

City of Oxford Licensed Taxi Cab Association secretary Alan Woodward said: “It is going to be a nightmare.

“But because of the length of time the work will take, there is no other time of year you could get it done that would be better.

“It will cause mayhem round the whole of the Oxford ring road for months and months. Only time will tell if it is worth it in the long run.”

Fellow cabbie Ghafoor Khan said: “It is going to cause complete chaos around Oxford if it is carried out at the same time as the Iffley Road work.

“It will obviously slow the traffic right down and hit commuters the hardest. It will double the travelling times to get anywhere.

“There will be a knock-on effect on all the surrounding roads.”

And driving instructor Richard Clapham, a member of the Institute of Advanced Motorists for 49 years, said: “I think it will be very, very difficult, certainly until people get used to what is going on.”

He added: “They do not do roadworks efficiently.”

Hugh Jaeger, from Bus Users UK campaign group, said: “It is going to be less than ideal to have both works carried out at once, but Heyford Hill certainly cannot be delayed.

“It is both worn-out and a cause of congestion.”

Sainsbury’s is paying for the work in a bid to improve traffic flows.

Spokesman William Wood said work was expected to start in mid-April.

He said: “The highway works will be managed to ensure that they are undertaken as efficiently as possible to minimise disruption, and we will ensure the local community is kept in-formed.’’ Oxfordshire County Council spokesman Owen Morton said: “We will look at the work as it unfolds within our capacity as the highways authority and we will work to keep disruption to a minimum.”