Pilot models of the Uber self-driving car is displayed at the Uber Advanced Technologies Center on September 13, 2016 in Pittsburgh, Pennsylvania.

Uber's Emil Michael says autonomous driving technology is being perfected at a faster rate than we think, but the challenge the company faces is finding enough test markets to get the cars ready for prime time.

Because driverless cars are brand new, governments haven't put rules in place to determine their legality. So Uber doesn't always know who's going to be welcoming until after it puts cars on the road.

"In most states and cities, there are no rules about driverless cars," Michael, a senior vice president at Uber, said on Wednesday at the Goldman Sachs Technology and Internet Conference in San Francisco. "Relationships with cities are hard sometimes, so you have to invest in a lot of them."

For example, Uber has had success setting up its autonomous driving experiment in Pittsburgh, where the company set up an Advanced Technologies Group in partnership with Carnegie Mellon.

