Many components of self-driving are at or near commercial readiness—freeway control, traffic jam handling, and auto-parking among them.

But while engineers speed toward road-ready future cars, it’s unclear that the rules of the road will be ready when the cars are. Politicians have made minimal progress in updating the legislation and regulations needed for the cars, which remain outdated and maddeningly inconsistent.

So what would Congress have to do to facilitate cars that could drive their passengers around?