SoftBank Fund Puts $2.25 Billion in G.M.’s Driverless Unit

The determination of G.M. and Waymo to offer ride services within months also suggests a conviction that businesses that use driverless cars to ferry ordinary people from place to place will spread rapidly and — absent the cost of a driver — yield hefty profits.

At the same time, Mr. Ramsey noted, “it’s a completely unproven business model,” with costly technology that is bound to have growing pains. The first vehicles will probably be programmed to be so cautious in traffic that crosstown trips may initially take much longer than people are used to, he said.

“I don’t think safety will be the concern for most people,” he said. “The time it takes to get to your destination could be a turnoff, though.”

Whatever bumps lie up the road, G.M. and Waymo appear to be ahead of some key competitors in the self-driving race. Uber, the ride-hailing service, suffered a setback in its efforts to develop autonomous taxis when a test vehicle struck and killed a pedestrian in Tempe, Ariz., in March. That prompted Uber to halt testing of self-driving cars in Arizona.

And Tesla and its driver-assistance system, Autopilot, have come under increasing scrutiny after a Model X sport-utility vehicle crashed into a concrete barrier later in March. The driver, who was killed, had Autopilot engaged; federal safety regulators are investigating. Since then, two other Tesla cars that had Autopilot running have been involved in nonfatal accidents.

Like G.M., Ford is racing to put self-driving cars into ride and delivery fleets, but it has a longer timeline and is hoping to have its car in production by 2021.

G.M.’s chief executive, Mary T. Barra, said the SoftBank investment validated the direction that G.M. and its Cruise division were taking. The investment gives SoftBank a 19.6 percent stake in G.M. Cruise and values the unit at more than $11 billion. That’s well above the $1 billion that G.M. paid two years ago to acquire Cruise as a start-up company.