The U.S. Postal Service on Tuesday started a test transporting mail across three Southwestern states using self-driving trucks provied by TuSimple.

San Diego-based TuSimple said its self-driving trucks will begin hauling mail between USPS facilities in Phoenix and Dallas to see how the technology might improve delivery times and costs.

The pilot program involves five round trips, each totaling more than 2,100 miles. The trucks will travel on major interstates and pass through Arizona, New Mexico and Texas. A safety driver will sit behind a truck's wheel to intervene if necessary.

TuSimple has raised $178 million in private financing, including from chipmaker Nvidia and Chinese online media company Sina.

Each truck is loaded up with an elaborate vision system combing radar, laser lidar sensors and multiple digital cameras, including one capable of tracking vehicles and road conditions up to 1,000 meters ahead, and a high-powered computing system developed by Nvidia.

The goal is to eliminate the need for a driver, freeing shippers and freight-haulers from the constraints of a worsening driver shortage. The American Trucking Associations estimates a shortage of as many as 174,500 drivers by 2024, due to an aging workforce and the difficulty of attracting younger drivers.

Last week, Swedish company Einride’s entered into freight delivery using driverless electric trucks on a public road.

On the other hand, companies such as General Motors Co unit Cruise, Uber Technologies Inc and startup Drive.ai have stumbled in building self-driving cars that can anticipate and respond to humans and navigate urban areas.