Over the last few months, Waymo’s robot taxis have become an unmistakable part of the San Francisco experience.

Once a novelty service that opened last year for limited downtown trips, Waymo rides are now open to the general public, ubiquitous on the city’s hilly roads. The company, which is owned by Google’s parent, Alphabet, has also expanded onto California freeways and into Los Angeles.

Waymo is now completing over 100,000 rides each week in San Francisco, Phoenix and Los Angeles — double the number in May. And on a July earnings call, Alphabet executives said the company planned to invest an additional $5 billion in Waymo.

But there is still a big question about whether Waymo’s robot cars can become a profitable business. And some wonder whether Waymo will one day move away from the business of managing car fleets and focus on selling its technology to other companies.

That Waymo has gotten to this almost-mainstream point can be credited to both the billions that Alphabet has spent on its yearslong autonomous vehicle project and its patience with the technology.

While robot taxi services are not profitable right now, Waymo and other autonomous vehicle companies like General Motors’ Cruise and Amazon’s Zoox are vying for a share of a market that could one day be worth as much as $5 trillion, some analysts estimate.