London mayor Boris Johnson has abandoned plans to introduce a Euro-4 NOx standard for trucks operating in the London Low Emission Zone (LEZ) in 2015, but buses will still have to comply.

The current phase 4 of the LEZ demands that trucks and buses meet only the particulates requirements of Euro-4, so older vehicles have been able to qualify by fitting filters that cut particulates but do nothing for NOx limits.

However, phase 5, due to start in less than two years’ time, would have meant any operators running pre-Euro-4 vehicles upgrading to meet the standards.

Limiting phase 5 to the TfL bus fleet is anticipated to save £350m in costs for businesses that would have had to upgrade their LGVs.

“Euro-4 arrived in 2006 so we’re talking about pre-56-plate vehicles, but there would have been some operators who would have had a problem,” said Natalie Chapman, FTA head of policy for London.

“If you want to make a difference to air quality in London at a reasonable cost, then buses are the obvious place to target,” said RHA director of policy Jack Semple. “They have big diesel engines, are rarely switched off, and are very thirsty.”

Johnson announced the changes last week as he unveiled his intention to create the world’s first Ultra LEZ.