The Highways Agency says it will soon plant its 52 millionth tree, as it continues a programme begun 50 years ago.
Announcing the planting ahead of the Tree Council's National Tree Week, the agency said it was now one of the biggest planters of trees in England.
Environmental advisor Tony Sangwine said National Tree Week came "at the end of a wonderful display of autumn colour on our busy highway network".
"It reminds us of the vital role that trees have to play in the sustainability of our transport links. They provide a rich habitat for wildlife, filter polluted air, stabilise the soil, reduce the impact of stormwater run-off and help to integrate roads with their surrounding landscape."
But Richard George, roads and climate campaigner for the Campaign for Better Transport, told elephant.co.uk news: "It's hard to find enough pinches of salt to take this announcement with.
"The Highways Agency spends its time planning road schemes through ancient woodland and encouraging people to damage the environment by driving further and faster.
"Planting trees is great - but planting them to make up for destroying the environment is like chucking a fiver to the RSPCA to make up for a lifetime of kicking the cat," he said.
The planting programme was begun in 1958 by the then Ministry of Transport, and taken over by the Highways Agency in 1994.
