Federal regulators cleared Amazon's Zoox to start charging fares in cars built with no steering wheel — and proposed letting robotaxis ditch the brake pedal next. The same boxy, controls-free vehicles have been driving San Francisco streets since last year.

The National Highway Traffic Safety Administration is rewriting decades-old rules that assumed a human sits behind the wheel, and San Francisco is a live test bed for the result. Zoox's purpose-built robotaxi — four inward-facing seats, no steering wheel, no manual controls — is one of the vehicles at the center of that shift, and it already operates here. As Washington moves to strip out the last physical safeguards, the question for a city that has spent two years hosting driverless fleets is who is actually watching the road.

Amazon's Zoox won federal approval Thursday to begin charging customers for rides in its specially designed autonomous cars, the Associated Press reported from Las Vegas. The distinctive boxy vehicles — with four inward-facing seats and no steering wheel — have been offering free rides in Las Vegas and San Francisco since last year. Zoox still needs state and local sign-off before it can turn on the meter in any given market.

The bigger regulatory shift is what comes next. NHTSA proposed a rule last month that would let robotaxis operate without brake pedals, according to the AP. That proposal is still pending. Most federal vehicle-safety standards were written in the 1970s, '80s and '90s, always assuming a human driver — and the agency is now deciding which of those requirements still apply to a car that drives itself.

"If you're going to be developing a standard in the 1970s, 1980s, 1990s, nobody at that time had this imagination, nobody had a crystal ball that you might have technologies that would enable the vehicle to drive itself," NHTSA Administrator Jonathan Morrison told the AP. Steering wheels, windshield wipers and side-view mirrors, he argued, aren't really needed in a vehicle with no driver. Morrison said the agency still intends to act as the "cop on the beat to make sure that this is being done right," adding: "Sometimes we have seen unsafe behaviors, and we jump on that really quickly again. That's our job at NHTSA."

The Verge independently reported Thursday that Zoox "can now charge for rides in its steering-wheel-free robotaxis." Zoox's own site lists San Francisco alongside Las Vegas, Austin, Miami, Atlanta and Los Angeles as markets where the vehicles operate.

For riders, the novelty tends to win out. Chloe Huu, visiting from Ann Arbor, Michigan, described her first Zoox ride on the Las Vegas strip to the AP: "It's kind of scary at first, but when I just got used to it, it's really cool and chilling. I really liked the music and how you can adjust the temperature." She added that the shifting wait-time estimate made the trip hard to plan.

San Francisco has less reason to treat the design as a curiosity. NHTSA itself recently warned that robotaxis interfering with first responders are "a danger to the general public," The Verge reported — precisely the kind of edge case where a human might once have grabbed the wheel or stomped the brake. Federal rulemaking that writes those controls out of the vehicle entirely is advancing while cities are still learning how driverless cars behave around emergencies.

There is also a gap between what Washington can decide and what San Francisco can. A NHTSA design rule can declare that a robotaxi doesn't legally need a brake pedal; it does not decide whether Zoox gets to charge fares in the Marina or North Beach. California's own approvals — through the Department of Motor Vehicles and the Public Utilities Commission — remain a separate gate, one that has repeatedly slowed paid, driverless expansion in the state. Both sets of approvals have to line up before the meter runs here.

That gap is where the local fight will play out. The physical controls now being written out of the federal rulebook are the ones a person reaches for when the software doesn't know what to do — and San Francisco, more than most cities, has watched what happens when it doesn't.