CRACKS in the pavement and a mysterious dip in the road at Frideswide Square have stumped Oxfordshire County Council bosses, who say even more work will be required.

Urgent investigations are taking place to figure out why the relatively new scheme is sustaining such high levels of damage.

Despite only being completed last December, the £6.7m project designed to cut traffic congestion has already seen workers out on a number of occasions to fix a variety of problems.

The council's major infrastructure delivery service manager Paul Fermer said cracks in the pavement outside Dominos Pizza, which saw workers digging up the pavement last week to fix the problem, had left experts flummoxed.

He said: "It's unusual and it has got everyone stumped.

"We are investigating what the cause could be. It could be something to do with the sub-soil for example but it's nothing obvious.

"Delivery trucks have been using that section of pavement and we will remind them to use loading bays - but that's not the cause, it should be able to take those sorts of vehicles."

The road has also started to dip near the bus stops and although it is not visible to the naked eye, Mr Fermer said it needed to be fully investigated.

He admitted a dip of this nature would not normally appear until the road had been used for several years and conceded should the problem be severe enough more road works on the key route will be required.

On top of that, the council has finally admitted the roundabout opposite the Royal Oxford Hotel was not big enough for large vehicles.

Mr Fermer said: "It's an innovative scheme which has pushed boundaries and the radii of the roundabouts had to be tight to encourage traffic to move slowly through the square.

"But we just made it a little bit too tight."

Last month, £30,000 was spent repairing damage caused by vehicles struggling to make it around without mounting the kerb.

This has now been fixed but despite similar problems at the roundabout near the train station, which will also need to be repaired, bosses remain adamant there is no design fault.

Mr Fermer insisted the radius of the roundabout was big enough and vehicles were travelling too fast causing them to over-run onto the pavement.

Oxford Bus Company and Stagecoach have both been vocal in expressing their concerns over the limited space its drivers had to manoeuvre in Frideswide Square.

In November 2015, shortly before the new layout was completed, the county council agreed to "tweak" its bus bays after the companies complained they were too small.

Oxford Bus Company, which said the roundabouts design made it "impossible" for its driver not to hit the kerb, said the space was still not ideal.

Managing director Phil Southall said: "We have let our views be known to the County Council on the design of the roundabouts. "We have maintained that the space for our vehicles to manoeuvre is sub-optimal in places but accept that it is their decision as to what arrangements prevail.

"We will work with the County Council to make this arrangement work as best we can."

A timetable for the necessary further repairs has yet to be drawn up as investigations are ongoing but it is understood contractors, Skanska, which is also working on the Cutteslowe and Wolvercote roundabouts, could be required to put up some of the cash should they be at fault for the damage.

Despite the bumps along the way the new layout has dropped the maximum queue length each morning along Hythe Bridge has been significantly reduced.

Board member for transport David Nimmo Smith apologised for the disruption but insisted the project had been a success overall.

He said: "I am sorry that these problems have caused further disruption to local businesses and I understand their frustration.

"We will be in touch shortly to inform them of the next steps we will be taking to put things right.

"The project has twice been shortlisted for national awards and the affected areas still amount to a small part of the overall square and the overall aim of creating a good public space with steadily moving traffic - especially for cyclists and pedestrians has been achieved."