Highways England has been trialling a scheme which has seen the speed limit cut on several UK motorways.
Designed to help reduce air pollution on roads with illegal levels of nitrogen dioxide, nine motorways have been affected and will see speed limits dropped to 60mph.
High No2 levels are dangerous to health, with poor air quality, in general, being linked to 40,000 deaths a year.
As part of the scheme, Highways England analysed the pollution levels of 101 roads earlier this year and found the areas surrounding 30 of the roads had air quality that was below acceptable levels.
Chief engineer at Highways England, Mike Wilson, said of the scheme that: “Poor air quality is the largest environmental risk to public health in the UK, known to have severe effects on vulnerable groups such as the elderly, children and those suffering with pre-existing health conditions.”
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“It can also be damaging to the environment, with negative impacts on animal and plant life.”
The roads being monitored as part of the speed-reduction scheme are the A38, M32, M6, M5, A1, M4, M1, M621 and M602.