Motorway speed limits are being cut to 60mph in an attempt to lower dangerous levels of air pollution, Highways England has said.
Sections of the M1 near Rotherham, the M6 near Witton and the M5 to Oldbury have all been given 60mph speed limits in recent months to reduce illegally high levels of nitrogen dioxide emissions.
Highways England will keep the change in place for the "foreseeable future" until pollution comes down to well below legal limits. A further four areas have speed limits in place for other reasons, such as roadworks, and will have 60mph limits imposed when those temporary measures end.
Highways England identified 30 areas of its road networks where levels of NO2 exceed legal limits of 40µg/m3.
That includes a section of the A3 near Guildford where limits are more than double the legal limit. Highways England is now considering the introduction of a 9.3-meter high barrier.
It is also planning to divert HGVs from two sections of the A500 to junction 15 the M6 during off-peak times. A section of the A38 north of Plymouth will also be considered for new lower speed limits once its levels of air pollution have been assessed.
NO2 pollution, produced by vehicles, has been linked to asthma and exacerbates other respiratory conditions.
Highways England said the "long-term" solution to pollution was the introduction of electric vehicles, which it is supporting in cities such as Nottingham and Bristol, including "try before you buy" electric van centres for local businesses.
But it admitted that in 17 of the 30 areas it had "no viable measures available" to reduce air pollution in a shorter time span.
Mike Wilson, the chief highways engineer at Highways England, said: "We are committed to supporting the Government to improve air quality alongside and near England’s motorways and major A roads. Air quality is within legal limits across the vast majority of our road network, and the picture is improving."