Low-income households need to spend up to 17% of their income to run a car, according to a report by the RAC Foundation.
The poorest fifth of British households spend a higher percentage of their income on driving than any other group, the research revealed.
Nearly half of these low-income households now have a car, but they also suffer disproportionately as the cost of motoring rises - and they will be hit hardest by increases in motoring taxation.
Taxes hit the poor more than the rich
Professor Stephen Glaister, the RAC Foundation's director, said: 'There's a feeling that raising more money from motoring tax is not a bad thing to do because it hits the rich rather than the poor, but that's simply not true.
'People used to think that poor people don't have cars, but now 49% of these low-income households own a car and they are most vulnerable to rising costs.'
Poor could be forced off the road
Britain has also adapted to higher rates of car ownership, with public transport suffering as a result making it increasingly difficult for people who don't have private transport to get to work, or even to use services such as hospitals.
As the cost of motoring rises, and governments consider imposing higher taxes on car use, the RAC Foundation warns that it's the poorest drivers who are going to be forced off the road.
Professor Glaister said: 'Everybody knows that we have to deal with the issue of carbon emissions, but we need to do so in a way that doesn't cause unexpected or ill-considered damage to particular groups in society.
'We don't want the government to impose new policies without being aware that they can cause particular difficulties. If the ladder of private transport is pulled up, then it's these poorer households that are going to be most severely impacted.'