Self-driving big-rig trucks are making their way to the Phoenix metro area as part of a testing program by Waymo.

Waymo, which has been testing and expanding a self-driving vehicle program in the East Valley for several years using minivans, will resume testing this week of big-rig trucks in the Phoenix area, said Suzanne Philion, a Waymo spokeswoman.

The trucks have been tested previously in Arizona, California and Georgia, Philion said.

"The principles are the same, but things like braking, turning, and blind spots are different with a fully-loaded truck and trailer," according to the Waymo website.

The driving will start on the freeways around metro Phoenix and continue to expand to other routes over time, according to Philion.

"Trucking is a vital part of the American economy, and we believe self-driving technology has the potential to make this sector safer and stronger," according to the Waymo website.

Waymo tested its self-driving trucks carrying freight, bound for Google's centers, according to the Waymo website.

Waymo officials declined to provide further details about the renewed testing, including specific days and locations.

Waymo, formerly known as the Google Self-Driving Car Project, has been operating autonomous vehicles in Chandler and nearby cities in the East Valley since 2016.