A 60mph speed limit is being imposed on some sections of motorway in England as part of a wide-reaching emissions reduction programme overseen by Highways England (HE).
In a new report, the infrastructure management body said that it's "committed to improving air quality in and around the Strategic Road Network (SRN)" and supports the government's ambition to reduce levels of nitrogen dioxide (NO2) in the atmosphere.
HE has partnered with the Department for Transport (DfT) and the government's Joint Air Quality Unit (JAQU) to monitor and, if necessary, modify 101 sections of the national road network where levels of NO2 exceed legal limits.
Of the 101 sections of road highlighted by the study, 30 were found to have above-average levels of NO2, of which eight now have a lower speed limit in place, in an effort to reduce the emissions generated by traffic.
The affected sections of road include part of the M1 motorway near Rotherham in Yorkshire, junctions 1-2 of the M5 in the West Midlands and a stretch of the M6 at Witton in Birmingham.
HE is also investigating other means of mitigating emissions around busy roads. On the A3 through Guildford in Surrey, for example, where NOx levels are at double the legal limit, it's working with the local council to determine the feasibility of a 9.3m-tall 'vertical air quality barrier'. It says the urban nature of this stretch of road makes such a device complex to install.
Meanwhile, a scheme in certain areas will have buses fitted with an exhaust filtration device that's claimed to lower their NOx output. Traffic-flow improvement schemes are also being investigated as a means of reducing idling time and congestion.
In some areas, HE has determined that it couldn't feasibly deploy emissions-reducing measures that would reduce NOx in a timeframe quicker than that already forecasted. This includes a section of the A34, which runs from Oxford to Southampton, where the body will "continue to investigate whether there are new or emerging ideas and/or technologies that could be considered".
Diversions of heavy goods vehicles in peak times on certain roads, are also being planned, with the requisite road signs currently being designed and installed for part of the A500 from Nantwich to Stoke-on-Trent.
HE forecasts that emissions levels will come down naturally as electric vehicles become more popular. It's supporting the switch to EVs with a scheme to incentivise electric van adoption in Bristol, Derby and Nottingham and has promised to accelerate EV charging infrastructure development from 2020-2025.
As part of a plan to make Britain's roads carbon-neutral by 2050, HE will install more efficient LED lighting across the network, make its own vehicle fleet fully electric and plant an additional three million trees by 2030.