MOUNTAIN VIEW, Calif. — Humans might be the one problem Google can’t solve.

For the past four years, Google has been working on self-driving cars with a mechanism to return control of the steering wheel to the driver in case of emergency. But Google’s brightest minds now say they can’t make that handoff work anytime soon.

Their answer? Take the driver completely out of the driving.

The company has begun building a fleet of 100 experimental electric-powered vehicles that will dispense with all the standard controls found in modern automobiles. The two-seat vehicle looks a bit like the ultracompact Fiat 500 or the Mercedes-Benz Smart car if you take out the steering wheel, gas pedal, brake and gear shift. The only things the driver controls is a red “e-stop” button for panic stops and a separate start button.

The car would be summoned with a smartphone application. It would pick up a passenger and automatically drive to a destination selected on a smartphone app without any human intervention.

Google won’t say if it intends to get into the car manufacturing business or simply supply technology to carmakers, but it says there are plenty of possibilities if it can persuade regulators to allow cars with no drivers. One potential use: driverless taxi cabs.