I wasn’t long in the backseat of Google’s self-driving Toyota Prius, cruising smoothly down California Highway 85, before a sober, gray-flannel question pierced my giddy techno-utopian buzz: Is this legal?

On principle, it would seem downright churlish to penalize Google’s upstanding Prius — which kept letter-perfect lane position, following distance and speed-limit compliance — while all around us human drivers committed a panoply of illegal acts: talking on their phones, speeding, changing lanes without signaling, tailgating, you name it.

But what does the law say about autonomous vehicles?