Google, File, Associated Press
This undated image provided by Google, shows an early version of Google's prototype self-driving car. Self-driving cars could reduce the number of vehicles a household needs and open up new commuting options for Americans, according to a report released Monday by the University of Michigan Transportation Research Institute.

DETROIT — Self-driving cars could reduce the number of vehicles a household needs and open up new commuting options for Americans, according to a report released Monday by the University of Michigan Transportation Research Institute.

By analyzing data from the government’s National Household Travel Survey, UMTRI researchers Brandon Schoettle and Michael Sivak found that families with three or more vehicles in their driveway rarely use more than one at a time.

After examining driving habits of about 150,000 households, they found that 83.7 percent of households had no trips that overlapped or conflicted on a typical day. Only 14.7 percent of households analyzed had two drivers with overlapping trips creating a need for two vehicles. In only 2 percent of those households were there enough overlapping trips to require three or more vehicles.

“We expected it would go in that direction, but we were surprised how extreme it was,” Schoettle said.

The study assumes that owners of self-driving vehicles will be able to return to the user’s home where another family member could run errands during the work day and send it back to pick up the day’s initial user when he or she left work.

If consumers responded to the flexibility by sharing vehicles to the maximum extent possible the UMTRI study concludes the average vehicle ownership rate could drop from today’s 2.1 to 1.2 per household.

“This is the most extreme possible scenario if everyone who could engage in vehicle sharing did so, but we know that won’t happen most likely,” Schoettle said.

Other recent studies have concluded that self-driving cars could add to traffic loads and sprawl.

Ken Laberteaux, a Toyota scientist, told Bloomberg last year that historically people have tended to live farther from their jobs whenever commuting is made easier. Self-driving cars could reverse the trend of millennials choosing to live in large cities where public transportation, bicycles and ride-sharing services are more accessible.

Depending on regulations and laws, autonomous vehicles could enable disabled people and even children to use a form of transportation not now accessible to them. That could drive up demand.

Even if the opposite occurs, as the UMTRI research suggests, automakers shouldn’t regard autonomous driving as a threat to sales. Schoettle and Sivak wrote that increased vehicle-sharing could lead to more miles driven per self-driving car.

“All things being equal, it’s kind of a wash. There’s a reduction in ownership, but you also have a rather large increase in vehicle usage and a need to replace them more frequently,” Schoettle said.

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