Zoox, Amazon’s self-driving unit, is bringing its autonomous vehicles to more cities. 

The self-driving technology company announced Wednesday plans to begin testing in Austin and Miami this summer. The two cities mark Zoox’s fourth and fifth test cities, following Las Vegas, San Francisco and Seattle. 

The news comes as federal regulators increase their scrutiny of self-driving car companies like Waymo and Zoox, both of which are under investigation over safety issues. Earlier this week, the National Highway Traffic Safety Administration requested more information from Zoox to aid its probe into rear-end crash risks posed by unexpected braking. 

That heightened scrutiny — fueled in part by a Cruise incident last year involving a pedestrian collision — might be part of the reason Zoox has been taking a slow and steady approach to testing and scaling. 

A Zoox spokesperson told TechCrunch that the company began mapping the cities this spring. Over the summer, Zoox will deploy its retrofitted Toyota Highlander test fleet with safety drivers behind the wheel “in small areas near the business and entertainment districts.” The company did not say how many test vehicles it would send to each city.

Zoox also didn’t say when it aims to remove the safety driver or begin commercial operations in Austin or Miami. Rather, the company is focused on using the different urban environments to fine-tune its autonomous system. For example, Austin has horizontal traffic lights, traffic lights hanging on wires, railway crossings and epic thunderstorms. Miami’s traffic lights are suspended diagonally across intersections and, apparently, the city is plagued with impatient drivers afflicted by road rage.

Zoox’s testing protocol is twofold: The company identifies specific pre-planned routes that offer challenging driving features and scenarios, while also randomly testing certain point-to-point routes within a defined geofence.

“We always start with a focused testing area, expanding methodically as our AI gets more familiar with the unique conditions in each city,” reads the blog post.

The plans to test in Austin and Miami come as Zoox gears up for its first commercial launch. Zoox has a permit to test its vehicles without a safety driver in parts of San Francisco and Foster City, and is targeting that market as one of its first launch cities alongside Las Vegas. 

Zoox did not respond to TechCrunch’s request for a timeline for commercial deployment or to provide definitions of the geofenced areas. 

Zoox has become associated with images of its purpose-built robotaxi, that cute, breadbox-shaped vehicle with no steering wheel or pedals and side doors that slide open to admit passengers. The company won’t be testing those vehicles on public roads in Austin or Miami, just yet. Zoox previously said it has begun limited testing of the fully driverless robotaxis on public roads in Las Vegas and San Francisco and plans to start offering rides to passengers this year. In February, the California Public Utilities Commission (CPUC) granted Zoox its driverless AV pilot permit, which allows the company to carry members of the public for free within the bounds of its approved Foster City domain. Zoox has not confirmed if it has begun doing that. 

Zoox’s expansion news comes as the robotaxi space gets a second wind. Or maybe it’s a third wind. GM’s Cruise has also recently announced plans to test its robotaxis in Dallas and Phoenix. Alphabet’s Waymo earlier this year began offering driverless rides to employees in Austin in preparation for a planned commercial launch this year, and the company also recently announced plans to begin robotaxi testing in Atlanta.