The U.S. Postal Service is testing its first long-haul self-driving delivery truck in a two-week pilot program that will use an autonomous semi-trailer to deliver mail between distribution centres in Phoenix and Dallas.

TuSimple, a self-driving truck company, is providing the vehicle and will have a safety engineer and driver in the cab to monitor its performance and take control if there are any issues, the company said in announcing the test this week.

 The US Postal Service has been exploring the idea for some time, recently soliciting bids to put semi-autonomous mail trucks on the road in a few years that allow a human to sort the mail while being autonomously driven along the route.

“We are conducting research and testing as part of our efforts to operate a future class of vehicles which will incorporate new technology to accommodate a diverse mail mix, enhance safety, improve service, reduce emissions, and produce operational savings,” said US Postal Service spokeswoman Kim Frum.

While nobody expects regulators to approve driverless semis anytime soon, the potential is enormous. It’s the reason manufacturers are working on self-driving semis. 

Tesla, which is developing an all-electric semi, has said all of its trucks will come with autopilot technology.

For the U.S. Postal Service, self-driving semis could provide a huge benefit. In 2018, the USPS had more than 5,500 prime movers and trailers in its fleet.