PROPOSED 20mph speed limits across the city could compromise road safety, a driving expert said after a trial.

A test-drive on the longest stretch of Oxford roads set to become 20mph also showed driving at slower speeds reduced fuel economy.

The new limits are set to become law on a swathe of city roads in August after the county council approved the £300,000 scheme last month.

To test its effect, we conducted an experiment with Richard Clapham, a driving instructor in the city for the past 24 years.

I drove Mr Clapham’s 1.5-litre Renault Megane on a 4.9-mile route from Ferry Hinksey Road in West Oxford (just west of a proposed 20mph scheme in the Botley Road) to the end of Old Road in Headington.

Mr Clapham took the wheel for the return journey.

The experiment started at 2.20pm on Thursday. Driving at 20mph compared to 30mph saw our journey times increase, our average speed drop by just over two miles an hour and our fuel economy fall from an average of 30.6mpg (miles per gallon) to 29.3mpg.

The fuel economy suffered most when driving up Morrell Avenue in second gear – due to the engine revving faster.

Mr Clapham, a member of the Institute of Advanced Motorists for 47 years and owner of Access Driving Services in Botley, also felt 20mph limits made driving less safe.

He said: “It was an interesting experiment. I would say safety is compromised because of the increased concentration on your speedo.

“It will be very difficult for anybody to drive at 20mph because I’m looking at a speedometer constantly and I should be looking at the car in front or the cyclist.”

Mr Claphamopposed 20mph limits in St Giles saying the road width made it suitable for a 30mph limit, but said a 10mph limit on sections of Cowley Road would be understandable.

He added: “To put blanket speed limits on roads is totally wrong. All roads are different and deserve to be treated differently with different speed limits where necessary.

“On some occasions you can be driving below the speed limit and still be driving too fast for the conditions.”

Mr Clapham said 20mph limits would be particularly frustrating at night as roads were empty and safe enough for motoring at higher speeds.

He feared more of his students would get overtaken by impatient drivers wanting to break the 20mph speed limit.

Overtaking cyclists at 20mph also proved a problem.

Mr Clapham thought collisions would be more likely to occur as cycles and cars spent longer side by side.

Geoff Barrell, of Oxfordshire County Council’s road safety team, said: “A pedestrian, if struck by a vehicle driving at 20mph, is likely to suffer slight injuries. At 30mph they would be severely hurt and at 40mph or above are likely to be killed.

Internationally accepted statistics prove that cutting speed by even a one mph average will deliver a five per cent reduction in casualties and if this saves one life in Oxfordshire, it will have been worth it.

“We are satisfied that a 20mph limit on those roads selected for the scheme will help reduce the number and severity of accidents, encourage walking and cycling and generally improve the environment for pedestrians Paul Cullen, spokesman for Life Begins at 20, which lobbied for new 20mph limits, said: “It is not true that driving at 20mph is less economical than driving at 30mph on Oxford’s roads, and if you are behind a cyclist then wait until it is safe to overtake.”

Colin Prickett, 57, a driver instructor for AA, in Headington, said: “Twenty isn’t an efficient speed to drive a car. If your fuel economy goes down, your CO2 emissions must go up, so it’s counter- productive to what we need to achieve.

“It should be left to drivers’ good sense to drive according to the road and traffic conditions.

“The traffic moves slowly enough in Oxford anyway.”