Transport became the largest sector for greenhouse gas pollution in 2016 as emissions overall fell 5% in a year, official statistics show.
Carbon dioxide, the main greenhouse gas, was down 6% between 2015 and 2016, with the reductions in pollution mostly down to a decrease in the use of coal for electricity generation, the data from the Business Department shows.
Emissions from energy supply plunged 17% year-on-year, while transport emissions rose 2% in 2016 and emissions from homes were up 4%.
Transport now accounts for 26% of the UK's greenhouse gas emissions, compared to 25% coming from energy supplies.
Since 1990, greenhouse gas emissions have fallen 41% in the UK, while carbon dioxide is down 36%.
But while emissions from energy supplies are down 57% since then, transport emissions are only down 2%, making it the worst performing sector.
The Government has announced ambitions to end sales of new conventional petrol and diesel cars and vans by 2040 as part of efforts to tackle climate change and air pollution.
The Committee on Climate Change, which advises the Government on meeting its long term legally binding climate targets, has said transport emissions must fall by 44% by 2030 to keep the UK on track to meet its goals.
The committee has called for 60% of new cars and vans to be ultra low emissions by 2030, most of which will be electric, as well as more action to make conventional vehicles cleaner and encourage more walking, cycling and public transport.