Major road schemes produce 10,000 more tonnes of carbon per year than predicted, according to the Liberal Democrats.
According to figures released following a Parliamentary Question, predicted and actual quantities of carbon released in 27 major projects vary widely.
The previously predicted carbon emissions started since 2002 generated 10,000 tonnes more carbon then expected.
Liberal Democrat Shadow Transport Secretary, Norman Baker said: “This Government continues to push ahead with massive road building schemes that cost millions of pounds more than predicted, as well as increasing traffic and carbon emissions.
“These huge schemes are responsible for thousands of tonnes of extra carbon emissions every year.
“This environmental disaster shows that the Government’s concern about climate change is little more than greenwash,” he said.