A growing number of states are taking up legislation that addresses self-driving vehicles in an effort to make it easier for researchers to explore the technology.

But most of the legislation deals with how states can facilitate testing — as opposed to consumer use of the vehicles — largely because truly automated vehicles aren’t yet available on the market. When that day comes, states will face a host of thorny questions. Historically, states have regulated drivers, and the feds have regulated vehicles. But what happens when the vehicle is the driver?