When Sen. Gary Peters traveled to South Korea this month, the Michigan Democrat was interested in more than U.S. efforts to stop nuclear weapons testing and development in the North.

The country — home to top auto manufacturers like Hyundai — is one of many investing in the burgeoning autonomous-driving industry. But without a clear regulatory framework in South Korea, the U.S. or elsewhere, the carmakers and technology giants that have invested billions of dollars lack rules for the road to commercialize their creations.