It’s still too early to give a definite thumbs up or thumbs down to promises of future driverless cars reducing private car ownership by acting as robot chauffeurs. But evidence from today’s ride-hailing services suggests that Uber, Lyft and Waymo may only worsen traffic congestion by crowding roads with robot taxis in the near future.

The latest study from the Metropolitan Area Planning Council Research in Boston found that about 42 percent of ride-hailing passengers in the survey said t