The speed limit will be cut on parts of four motorways before October in a trial to reduce pollution, Highways England has said.

It will be reduced from 70mph to 60mph in areas that have seen higher than recommended levels of nitrogen dioxide.

The trial will take place on stretches of nearly five miles.

It will be on M6 junctions 6 to 7 by Witton, M1 junctions 33 to 34 by Rotherham, M602 junctions 1 to 3 by Eccles and M5 1 to 2 by Oldbury.

Nitrogen dioxide (NO2) released from car exhausts is a serious air pollutant and indirectly contributes to the warming of the planet.

The impact of the new 60mph limit will be reviewed in a year's time

Ivan Le Fevre, head of environment at Highways England said: "Ultimately the air quality challenge will be solved 'at the tailpipe' by vehicle manufacturers and changes in vehicle use.

"Until this happens we will continue our extensive programme of pioneering research and solutions."

Hybrids

The Department for Transport said the trial was among a number of measures to improve air quality.

As part of a plan to bring down NO2 levels, the government aims to end the sale of all new conventional petrol and diesel cars and vans before 2040.

It has been consulting on bringing this forward to 2035, or earlier if a faster transition appears feasible, as well as looking at including hybrids for the first time.

The consultation's outcome will be announced at a later date.

Source: BBC