Dirty Downside to Driverless Cars Revealed in Study

Google's Driverless Car
A Google Inc. driverless car. Source: Google Inc. via Bloomberg

Driverless cars better be able to refuel themselves. They’ll consume more energy than cars with drivers.

That’s the somewhat counterintuitive conclusion in a new study by researchers at the University of Michigan in Ann Arbor. They say that autonomous autos could reverse a years-long trend of declining fuel consumption.

At least a half-dozen car and technology companies, from General Motors Co. to Google Inc., are developing the futuristic vehicles, which would be guided by sensors and satellite positioning. Baidu Inc., the Beijing-based search-engine company, said Monday it could have a model on the road this year.

Here’s how they’d use more energy than conventional cars: more trips. In most households, each adult commutes, runs errands and shuttles the kids separately, according to the U.S. National Household Travel Survey. A self-driving car would make more trips to finish the same tasks, the University of Michigan researchers said. It might drop off one parent at work, return home to pick up the other, and then take the kids to school, return home, then start the return cycle.

What isn’t known yet is how many people who don’t currently drive, like kids and users of public transportation, will start sharing a self-driving car. Those new trips -- and all the return trips in between -- could mean more total driving.

Regular gasoline at U.S. pumps dropped to $2.447 a gallon on March 10, according to Heathrow, Florida-based AAA, the nation’s biggest motoring group.

Flooring It

Increased sharing could mean Americans would own 43 percent fewer cars (from 2.1 to 1.2 vehicles per household) but use them 75 percent more (from 11,661 to 20,406 annual miles per vehicle), according to calculations by Brandon Schoettle and Michael Sivak of the University of Michigan Transportation Research Institute. Their funding comes from federal and state government agencies and auto manufacturers and suppliers.

“It could be that sharing the vehicle ends up increasing the mileage because of all these connecting trips,” Schoettle said. “The net effect is probably going to be an increase in mileage, and in general the more miles you drive the more fuel you burn.”

There’s a caveat. Automated cars might prove to be better at conserving fuel because they wouldn’t waste fuel flooring the accelerator and slamming on the brakes, like humans do, Schoettle said. They’d be better at avoiding traffic jams and red lights, and would find parking spots without driving around and around and around. Also, ride-hailing apps like those offered by Uber Technologies Inc. and Lyft Inc. could make sharing more efficient. “Shared autonomous vehicles” could use 12 percent less fuel and release 5.6 percent less climate-warming gas than average cars, according to a 2014 study by researchers at the University of Texas at Austin.

Robot Car

The race to bring the first robot car to market intensified with Baidu’s announcement. Google showed off a prototype self-driving car in December. Mercedes-Benz and Volkswagen AG’s Audi unit are testing them, too. Others, such as Toyota Motor Co., Honda Motor Co. and General Motors, are developing technologies to assist, if not replace, human drivers. Tesla Motors Inc.’s Model S has an “autopilot” mode. Apple Inc. revealed last month that it’s also working on an electric car, although it’s unclear what automated features it might have.

Alternative Fuels

What’s also unclear are the regulatory hurdles the invention might have to overcome. Five states have passed laws allowing them, with certain conditions, and six more are considering them, according to researchers at Stanford Law School.

Alternative fuels, such as electricity or hydrogen, will probably be part of future driverless cars, said Schoettle, the Michigan researcher. Even so, the additional energy has to come from somewhere, and coal and natural gas supply most of the country’s power.

“The upside is that vehicles could drive much more efficiently,” said Ethan Elkind, associate director of the Climate Change and Business Program at the University of California at Berkeley. “The downside of course is you may see more people driving. More driving overall is not a great thing for the environment.”

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