Moments later, a white Lincoln MKS rolled along a straightaway at about 25 miles per hour, swept around a wide left turn and negotiated its way through the downtown. Later, the cars stopped side by side under a green highway sign indicating a nonexistent ramp for I-96 to Lansing. There, the occupants stepped out to examine the rooftop sensors. After a long pause, the two cars repeated the same trek at a deliberate pace — much more slowly than the cars traveling on the public roads surrounding the site.

The testing is being conducted with the utmost care because the number of unanticipated challenges that arise on the road is almost limitless — a fallen limb, black ice, a reckless driver, a toddler in the street.

“There are real and significant questions about the safety of new technologies,” Mark Rosekind, administrator of the National Highway Traffic Safety Administration, said at an April 27 meeting in California. “The old model of counting vehicle miles and counting crashes and injuries is not sufficient.”

This month, the safety agency, which has limited authority to regulate the practice of test-driving autonomous vehicles on public roads, cautiously gave approval to several companies to begin testing on public roadways.

But the industry is not waiting around.

In addition to its Mcity effort, the University of Michigan is a partner in a project to set up a much more complex site about 10 miles away in neighboring Ypsilanti. It will be called the American Center for Mobility and will comprise 335 acres that were once part of G.M.’s Willow Run plant. During World War II, it was the site of a famed bomber factory. Mr. Maddox has been named the center’s chief.

Unlike Mcity, this larger site will have long stretches where autonomous cars can be tested at highway speeds and space for creating a variety of complex intersections. Its existing roadways include overpasses and bridges.