As a legal dispute ensnares Uber Technologies Inc.’s robot-trucking division, several startups are showing off their own efforts toward self-driving delivery vehicles that would reinvent the freight business.

While much of the autonomous-vehicle attention has centered on the race to embed the technology in everyday cars—involving auto makers such as General Motors Co. and BMW AG and tech giants such as Uber and Alphabet Inc.’s Waymo—another school of thought is that trucking—whether it’s long-haul or across town—is ripe for...