Zoox in March expanded the environmental conditions its AVs can handle on public roads to include "nighttime driving, driving under light rain and damp road conditions, and at speeds up to 45 mph," a spokesperson told CNBC.

The company's vehicles can carry four adults and luggage comfortably, and the small shuttles feature calming lighting, ambient music and interior cameras to monitor what's happening inside the cabin. Some early riders have described the look of the Zoox vehicles as "futuristic hot dog toasters" or "toasters on wheels."