by The 60mph speed restrictions on the M1 and M6 will be removed after National Highways admitted air pollution would be “ultimately solved at the tailpipe”.
From 2021, drivers have been required to slow down on stretches of motorway such as the M1 between junctions 28 and 35a in order to find out if driving more slowly helps reduce emissions.
The restrictions were supposed to last between 12 and 15 months, with National Highways promising that data showing whether the schemes were working would be available last spring.
On Friday, the body said the sections would return to the national speed limit of 70mph after pollution in the areas fell, but could not say whether this was because of the trials or because there were more cars electric and hybrid on the road.
Angela Halliwell, National Roads’ carbon and air quality group leader, said: “The general trend is that air quality is improving across our network. Removing 60mph speed limits from parts of the M1 and M6 where air quality has improved is a positive step.
“Ultimately, vehicle manufacturers will solve air quality ‘at the tailpipe’ and changes in vehicle use.”
A new report released by National Highways this week shows that levels of nitrogen dioxide in the Rotherham speed limit zone have fallen from 39 micrograms per square meter (µg/m3) to 35 µg/m3.
Similarly, pollution in Manchester has decreased from 38 µg/m3 to 31 µg/m3.
National Highways said it was “very likely” pollution would exceed the legal limit if restrictions were lifted, but could not say how it reached that conclusion. He said he would continue to monitor both sites.
However, the report also shows that pollution levels have increased in some areas with speed restrictions, including the trial site at the M602 at Eccles, and the M4 at Hillingdon. Nitrogen dioxide levels remained unchanged on the M5 at Oldbury.
Driving groups have previously warned that speed restrictions could increase congestion and worsen pollution.
National Highways said many factors affected air quality and that construction work close to the speed restriction areas may have been activated.
When the body was asked what they thought was the reason for the increase or decrease in pollution in the different areas, the body said: “We generally don’t know.”
Earlier this week, National Highways refused an SF request from the Telegraph to see the latest modeling and analysis for the 60mph zones, claiming the experts needed a “safe space” to do their work.
Although the company accepted that the information was in the public interest, it responded: “Although this issue is alive, a safe space is needed to reflect, continue the ongoing analysis, and make decisions about information.
“At this time, the release of some of the analysis could lead to a misunderstanding of the facts and impacts.
“Therefore this would not allow for a reasoned and informed discussion, with internal stakeholders or members of the public as to whether or not speed limits introduced for air quality should be maintained.”
Experts called for the remaining borders to be scrapped too if there was no evidence they were working.
‘arbitrary reductions’
Bob Bull, chairman of the British Drivers’ Alliance, said: “The practice of 50 and 60 mph limits on motorways does not seem worthwhile for air pollution reasons but is such a frustration and an obstacle to the safe flow of vehicles.
“Since no results have been published, despite promises that they would be available a year ago, it can only be assumed that the evidence does not support the arbitrary reductions.”
The lowering of the speed limit was introduced based on modeling which claimed that it would significantly reduce the average annual concentrations of nitrogen dioxide in the zones concerned.
It was suggested that this would help the areas around the trials near Rotherham in South Yorkshire, Witton in Birmingham, Eccles in Greater Manchester and Oldbury in the West Midlands meet pollution limits a year or two earlier than expected.
The Telegraph understands that the modeling did not take into account particulate pollution produced by braking. The policy also penalizes electric vehicles that produce no exhaust emissions and newer, less polluting cars.
Critics, former roads minister Sir John Hayes, have already said National Highways should show the trial was working or reinstate the national speed limit.
The AA argued that the most polluting vehicles, such as large lorries, were already limited to 60mph anyway, and police forces often allowed 10 per cent plus 2mph away from the speed limit, meaning drivers could still driving close to 70mph during the tests.
