Given technical and regulatory challenges, it may take a decade before fully self-driving cars can be used on U.S. highways. But May Mobility, a start-up based in Ann Arbor, Michigan, has already put its self-driving shuttles to work in downtown Detroit.

Founded in 2017 by auto engineers Edwin Olson, Alisyn Malek and Steve Vozar, the company recently scored $11.5 million in seed funding from the venture arms of BMW and Toyota, and major early-stage firms including Maven Ventures and Y Combinator.

Unlike, Alphabet's Waymo, GM-owned Cruise or Tesla, which are all working on level-5 autonomous vehicles, May Mobility's electric shuttles were designed to move along short routes that have been mapped inside of a 10-square-mile footprint. For now, anyway, the buses operate with a human monitor on board.

When needed, the start-up installs sensors and car-readable "stickers" along the shuttle routes. Adding such markers can help the shuttles better understand their environment and more safely navigate through bad weather or around unpredictable pedestrians, bikers and obstacles.

May Mobility's electric "microbuses" drive at a mellow top-speed of 25 miles per hour, not highway speeds.