Waymo, Google's self-driving car company, is moving beyond driverless taxis. The company announced on Friday that its self-driving trucks have begun hauling real cargo in the Atlanta area. A safety driver in the truck will take over if anything goes wrong.

"Over the past year, we’ve been conducting road tests of Waymo’s self-driving trucks in California and Arizona," Waymo wrote in a blog post. Now the trucks are going to haul loads to Google's data centers in the state of Georgia.

Waymo already announced in January that it was expanding testing of its self-driving taxi service to the Atlanta area.

Waymo's trucks will have plenty of competition. Earlier this week, Uber announced that its driverless trucks would begin hauling freight in Arizona—also with a safety driver in the truck.

Meanwhile, a startup called Starsky Robotics announced an initial test this week of its technology for remotely driven trucks. Another startup called Embark has been hauling real cargo with autonomous trucks (and a safety driver behind the wheel) since last fall.

Waymo hasn't provided much detail about its driverless truck tech, but there's reason to believe it may be more advanced than what its competitors have developed so far. The other three companies we've mentioned—Uber, Starsky, and Embark—have all focused on freeway driving, which is generally considered the easiest type of driving to automate.

Uber uses a "transfer hub" model, where a human driver takes a trailer through busy city streets at the beginning and end of a trip, while a self-driving truck drives a long-haul, freeway-only route in between. Starsky envisions trucks driving autonomously on the freeway, but having a human driver driving the truck remotely at the beginning and end of the trip.

"Embark is also focusing on handling freeway driving, with a human driver on board who navigates city streets," TechCrunch wrote last summer.

Initially, Waymo will have a safety driver behind the wheel just like these other companies. But Waymo's ambition has long been to develop "level 4" vehicles that can handle complex traffic conditions on city streets. Last November the company was confident enough in its driverless minivans to take the safety driver out of the driver's seat.

Waymo says it uses the same technology for its trucks, so it's a good guess that the company is aiming to achieve the same level of autonomy for its trucking fleet. That would mean a truck that can drive itself all the way from one loading dock to another—no safety driver, transfer hub, or remote operator needed.

"Things like braking, turning, and blind spots are different with a fully-loaded truck and trailer," Waymo writes. The company still has work to do, but starting with the industry-leading software in its minivans gives Waymo a significant head start.