Variable speed limits needed on motorways to cut pollution, experts say

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Such a move could reduce harmful emissions from cars, they said.

New draft guidance from the National Institute for Health and Care Excellence (Nice) sets out a series of steps that need to be taken to reduce the harmful effects that air pollution is having on the nation”s health.

Around 25,000 deaths a year in England can cite air pollution as a contributory factor – almost 5 per cent of all deaths, Nice said.

The health watchdog has proposed a series of initiatives to help improve outcomes across the country including; promoting smoother driving, encouraging house builders to place living rooms at the back of houses away from roads, and hedgerows to protect cyclists using cycle paths.

Local planners have been urged to consider that some speed bumps could be causing higher emissions because instead of encouraging a slower speed, drivers tend to accelerate and decelerate towards them.

Meanwhile, “no-idling” zones should be installed around the nation”s schools to prevent parents leaving their cars running during school drop offs.

In its new draft guidance for England, Nice has also called for a review of trees lining streets in urban areas because evidence suggests that “in some cases they restrict street ventilation causing poorer air quality, in others they improve it”.

Provisional figures show that road usage is at record levels, with an estimated 320 billion vehicle miles travelled on Britain”s roads in the year ending September 2016.

Road traffic is estimated to contribute to about a third of air pollution in urban sites.

The new Nice guidance advocates that local planners should “consider using variable speed limits and average speed technology on the roadside to promote a smoother driving style”.

Professor Mark Baker, the director for the Centre of Guidelines at Nice, said: “If the traffic is such that you are stopping and starting, decelerating and accelerating, then that increases emissions, pollution and fuel consumption.

“In those circumstances, slowing everything down to 60mph or 50mph is the best approach – but not all the time.

“That”s why variable speed limits are far more sensible than blanket 50mph or 60mph [limits].

“Variable speed limits are useful where at times the volume of traffic results in unhealthy driving conditions – which is stopping and starting.

“So M25 most of the time, M4 on a Sunday, M1 on a Friday evening.

“Variable speed limits are justified on roads which are busy enough for traffic to have to break for no other reason than that [the road is] blocked.”

Dr Nigel Jenkins, Nice”s guideline committee expert, added: “The ideas behind variable speed limits and average speed control is to try and improve the flow of vehicles.

“Having a more consistent flow of vehicles improves fuel efficiency as well as emissions form the vehicle, in effect reducing them.”

Ralph Bagge, leader of South Bucks District Council and deputy chairman of the guideline committee, added: “Smooth driving reduces emissions and stop-start acceleration and deceleration braking is harmful.

“It is putting out more through the tail pipe but secondly braking is also grinding bits of very fine particulate matter which goes into the atmosphere.”

Figures released earlier this year showed that average speed cameras are monitoring drivers on more than 250 miles of Britain”s roads.

Sections covered a range in length from just a quarter of a mile on London”s Tower Bridge to 99 miles on the A9 between Dunblane and Inverness, according to research from the RAC Foundation

The first section of road to become permanently managed by average speed cameras was on the A6514 ring road in Nottingham in 2000.