My feeling is that, in the US, automobile regulations are derived from horse and carriage regulations. When the horse was pulling the cart, it could get spooke

My feeling is that, in the US, automobile regulations are derived from horse and carriage regulations. When the horse was pulling the cart, it could get spooked and run off, killing or injuring pedestrians. Even though the driver nominally has control of the horse, the horse is an independent entity. This limited the liability of the driver. For example, if the horse ran off and killed someone, as long as the driver stuck around to explain, they wouldn't suffer very much in terms of consequences. It seems today that automobiles, although not an independent entity, still get the same kind of protections as a horse does. That's why and automobile driver who kills a pedestrian in the street can basically get off scot-free, even though the driver has full control over the automobile at the time.