The work is preliminary at the moment, as Waymo referred to it as "a technical exploration into how our technology can integrate into a truck." Others, meanwhile, are into more advanced testing -- Daimler, Volvo and others participated in an advanced autonomous "platooning" convoy challenge, for instance.
However, it may be arch-rival Uber that most motivated Waymo. The two companies are locked in pitched court battle, with Waymo having sued Uber for allegedly stealing some of its self-driving ideas. Uber's tech comes via its purchase of Otto, a self-driving company founded by Anthony Levandowski, one of Google's key self-driving executives. Earlier this week Uber fired Levandowski, shortly after federal prosecutors recommended an investigation into the alleged IP theft.
Despite all the problems, however, Uber has a lead over Waymo in the self-driving truck game, having done a 200-mile beer run in Colorado with no driver intervention. It also arguably has a big head start in logistics, having already developed an extensive ride-sharing network for its Uber passenger service.