Low-emission buses are being introduced for journeys along one of Scotland's most polluted streets.

Lothian Buses is to use a fleet of 30 new vehicles on the route through St John's Road in Corstorphine, Edinburgh, which is an air quality management zone.

The Euro 6 Volvo double-deckers will operate on the 26 services, which runs between the west of the capital and East Lothian.

All buses on the route, which also travels through air quality management zones in Princes Street and Musselburgh High Street, will be low emission by the end of 2018.

A report published last year showed 65 microgrammes of nitrogen dioxide per cubic metre were detected in St John's Road in 2015, making it the most polluted in Edinburgh.

The new vehicles are part of a £7m investment and Lothian said the fleet will reduce CO2 emissions by 25%, nitrous oxides by up to 98% and particulates by around 75% compared with the existing fleet.

The buses will also have USB charging points on board.

Richard Hall, managing director of Lothian, said: "St John's Road has always been a main artery within the city that we had earmarked for improvement and investment.

"The introduction of 30 new low-emission buses to this route, combined with our ongoing fleet replacement strategy BUS2020, ensures that we as a business are doing our part to improve air quality across the city.

"Buses are the lifeblood of the city and economy, transporting thousands of customers every day."

The announcement was welcomed by Edinburgh City Council and Friends of the Earth Scotland.

Charity campaigner Emilia Hanna said: "We welcome Lothian's launch of a cleaner 26 route along the St John's Road corridor, which is Edinburgh's most polluted street.

"Air pollution is still a public health crisis in Scotland, responsible for over 2500 early deaths each year.

"Buses are a key part of the solution to air pollution and are essential for the majority of Edinburgh residents who do not travel by car.

"One full double-decker bus can hold the equivalent number of passengers as 75 cars can so buses are a clear winner when it comes to tackling congestion and toxic air pollution, especially when they offer a clean and comfortable experience."