© Alamy
■ At first glance vegetable oil is a great idea, because growing the plants used to make it absorbs at least as much carbon dioxide from the atmosphere as the oil emits when it’s burned – it’s carbon neutral, in other words. But there’s nowhere near enough waste vegetable oil to fuel all the cars in the world, so plants would have to be grown specially. This raises a whole new set of problems, such as taking land usage away from food production and forestry. All in all, it’s better to ditch internal combustion altogether in favour of electric vehicles. AM