Friday morning I was in traffic, waiting for the light to change. Next to me, five cars in a row made a right turn. Four of them had either an Uber or a Lyft sticker on their windows. The fifth had both.

It’s no surprise to hear that ride-service cars are all over San Francisco. If anything, there are more than you might think. As The Chronicle’s Carolyn Said has reported, in April the San Francisco treasurer’s office sent notices to 37,000 people it had identified as San Francisco ride-service drivers, giving them 30 days to obtain a business license. (That deadline has since been extended to the end of this month.)

There’s been lots of discussion about whether the drivers are actually a business of their own. But I’d concentrate on the number: 37,000. That’s an immense change in options for personal transportation.

Consider how few taxicabs have traditionally been on the streets. For years the number of taxi “medallions,” which are basically licenses to operate a cab, has been held down. At present, the city has about 1,900 medallions — up from 1,500 a few years ago — and is gradually raising the number to 2,100.

Now, more than one driver can use a car with a taxi medallion. Theoretically, the cabs could be running 24 hours a day. But there’s still the limit to the number of taxis on the streets.

That created a well-documented problem. With a limited number of taxis, some drivers concentrated on downtown hotels, hoping to get a “golden ticket” ride to an airport. In addition, residents on the west side of town found drivers were reluctant to come all the way out to the outer avenues to pick up riders.

Lyft and Uber have turned that on its head. Even if the treasurer’s numbers include people who drive for Uber or Lyft only part time, 37,000 cars is a huge increase in available options.

And it’s only increasing. San Francisco’s chief economist, Ted Egan, presented a report in July on the so-called “gig economy,” meaning people who work on their own, a job at a time.

“There are indications that the use of online platforms in San Francisco is growing rapidly,” Egan said. “For example, the ride-sharing company Lyft reports a 450 percent growth in the number of San Francisco residents applying to drive for the company, between the end of 2013 and June 2016.”

With no cap on the number of those drivers in the city, we’re looking at a sea change in personal transportation.

At a panel discussion on corporate transportation at the urban think tank SPUR on Thursday, Rob King of Airbnb said his company’s 1,700-person workforce uses ride-hailing companies extensively.

King, who is Airbnb’s facilities coordinator, says he worked out a deal with Lyft where employees can travel to one of Airbnb’s two workplaces without paying.

“The (Lyft) app knows those two places and knows not to charge them,” he said. “Then we get billed at the end of the month.”

The idea has been a success. King said that while the largest number of Airbnb employees, 27.4 percent, get to work on public transit, the second-largest group uses ride-hailing services, 19.1 percent.

Surely options will only increase. Both King and Lauren Bennett, a transportation manager who was at the panel to represent the 22,000 employees at Salesforce, said the relatively new service Chariot, which uses vans, gets high marks from employees who have used it.

Chariot asks riders to create their own commuter routes online. When enough riders sign up for a route — currently the site says it is 112 riders away from starting a route from the Sunset to downtown and Caltrain — Chariot puts it into operation, charging just $3 a ride. Compare that to the often gritty Muni at $2.25.

That’s great. Bennett and King both say they offer employees limited parking options to discourage people from driving. The good thing, Bennett says, is their workers already buy into the idea.

“In San Francisco, getting people out of cars is not my challenge,” she said.

But once out, they need transportation. Bennett and King talk about solving the problem of the “last mile,” meaning the trip from a BART station, for example, to headquarters. Ride-hailing services are becoming a big part of that.

But you also have to wonder what the effect is on traffic congestion. An Uber driver isn’t going from point A to point B and parking. He is staying out on the street, looking for passengers. Add those 37,000 cars to the traffic grid and it has to have an effect.

So, the next time one of those clueless drivers stops in the middle of the street, holding up traffic to let a rider out, it’s not just annoying.

It may be the future.

C.W. Nevius is a San Francisco Chronicle columnist. His columns appear Tuesday, Thursday and Saturday. Email: cwnevius@sfchronicle.com Twitter: @cwnevius