As more automakers and researchers test cars that can drive autonomously, the National Highway Traffic Safety Administration has released a guidance document outlining recommended rules both for the vehicles themselves, and for drivers operating them. The guidelines are not laws, but could be used as the basis for laws in the future.
NHTSA says it recognizes five different levels of vehicle automation, each of which may be subject to different laws in the future. Level 0, or "No Automation," concerns cars in which the driver has full control over steering, braking, and acceleration. These cars can include warning systems, like lane departure or blind-spot monitors, but cannot automatically take action on behalf of the driver. Level 1, called Function Specific Automation, allows some features that can temporarily take control away from the driver. Examples include electronic stability control or brake precharging. However, such systems must not allow "the driver to be disengaged from physically operating the vehicle by having his or her hands off the steering wheel AND feet off the pedals at the same time."
Level 2, Combined Function Automation, concerns features like lane-centering or adaptive cruise control. The driver can take his hands or feet off the controls temporarily, but must be ready to take over from the automated system without any warning. This is the most common level of autonomous driving currently available -- most major automakers offer adaptive cruise control on luxury models. Level 3, Limited Self-Driving Automation, requires the car to drive itself completely, but to give control back to the driver if the car cannot keep driving safely. In that case, the car must warn the driver with enough time that he or she can prepare to begin driving again. NHTSA says that Level 4, Full Self-Driving Automation, is a system that can take over all driving functions without any human interaction. Hypothetically speaking, a car's occupant could safely nap while the car handled all driving tasks.
Suggested Testing Regulations
NHTSA also issued a set of guidelines it recommends for states that want to allow autonomous vehicles to test on public roads. (It's worth noting, however, that several states have already granted such permits without NHTSA's input.) Above all, the regulatory agency wants states to require special driver's license endorsements for anyone operating an autonomous or semi-autonomous car. Getting those endorsements would require the driver take lessons and tests on the capabilities and limits of the autonomous vehicle, as well as how to take over control in an emergency.
Other recommendations include state limitations on where and in what types of conditions autonomous cars can operate on public roads, requirements that the cars operate for a certain number of miles on private roads before use on public roads, and a system to record and report any failures or accidents of autonomous cars.
Above all, NHTSA warns that self-driving technology should only be used for testing because it, "is not yet at the stage of sophistication or demonstrated safety capability that it should be authorized for use by members of the public for general driving purposes."
Nonetheless, NHTSA's guidelines hint that the agency could one day enact laws requiring some sort of semi-autonomous technology. When research showed the safety benefits of electronic stability control, for instance, it was mandated on every new car sold after model year 2011. NHTSA is currently testing automatic braking systems, which can slow or stop a car before a collision, to see whether they should be mandated in new cars.