Self-driving “robocab” taxis could deliver huge environmental and economic benefits by running more efficiently than privately operated vehicles, a study has shown.

Scientists found that an electric self-driving taxi in 2030 would generate greenhouse gas emissions 90 per cent per mile lower than a privately operated petrol-powered car.

Its contribution to greenhouse gases would also be up to 82 per cent lower than a hybrid vehicle.

Almost half the savings were attributable to “right sizing” – tailoring the size of a taxi to its occupancy needs so that a single passenger travels in a smaller vehicle than a party of four.

Lead scientist Jeff Greenblatt, from the Lawrence Berkeley National Laboratory in California, US, said: “When we first started looking at autonomous vehicles, we found that, of all the variables we could consider, the use of autonomous vehicles as part of a shared transit system seemed to be the biggest lever that pointed to lower energy use per mile.”

Huge savings even without considering all effects

An economic analysis was also carried out to determine how cost-effective autonomous taxis would be. At 12,000 miles per year ,electric vehicles were still expected to be more expensive than owning and operating petrol-driven cars.

But if a vehicle was driven 40,000 to 70,000 a year –­ not unusual for a taxi ­– power delivered by a hydrogen fuel cell or electric battery was the most cost-effective option.

By 2030, autonomous taxis could be far cheaper to operate than driven ones, said the researchers, whose findings appear in the journal Nature Climate Change.

Self-driving cars were able to drive closely behind each other to reduce wind resistance, follow the most efficient routes, and provide smoother acceleration and braking.

“These are all incremental, but they do add up,” Dr Greenblatt said. “However, we didn’t even include these effects in our baseline results, and we still get huge savings without them.”