Tesla's Autopilot is not a 'self-driving car'

Tesla Model S Autopilot

Tesla's "Autopilot" system can do some impressive things. It can steer a car through traffic, and execute passing maneuvers with no involvement from the driver other than a flick of a turn-signal stalk.

But while it does enable some autonomous driving, Autopilot does not turn a Tesla Model S or Model X into a self-driving car. Autopilot's capabilities are limited, and Tesla was quick to emphasize those limits when it released the system in "public beta" form last October. At the time, Tesla CEO Elon Musk said Autopilot worked most effectively in dense traffic, on roads with very clear lane markings.

Even in a best-case scenario, though, he advised drivers to keep their hands on the wheel and stay alert at all times.

Tesla Autopilot suite of features - with version 7.0 update

He also noted that Autopilot's capabilities were limited by rain or snow.

Aside from its functional limits, Autopilot is also missing a feature crucial to self-driving cars.

Autopilot isn't connected to a car's navigation system, so it can't simply follow a route while the driver takes a nap, notes a recent Forbes review of the tech.

That puts Autopilot very low on the scale of vehicle autonomy defined by the U.S. National Highway Traffic Safety Administration (NHTSA). The scale includes five levels of autonomy, and seeks to clarify the difference between fully-autonomous cars and vehicles with some autonomous capabilities. Level 0 means a car has no autonomous systems to speak of, or advanced driver aids that intervene to provide assistance.

Tesla Autopilot sensor system

Level 1 encompasses cars with those advanced driver aids, including electronic stability control and systems that pre-charge the brakes in anticipation of a collision, that assist the driver but do not take over control of the vehicle. A Level 2 vehicle features automation of at least two control functions that work together, allowing the driver to cede limited control. With its ability to maintain a set distance from a car ahead and keep a car centered in its lane, Autopilot seems to fall into this category.

To move up to Level 3 autonomy, a car would have to be able to follow a route and drive itself without any human involvement, albeit only in certain situations. Cars with Level 3 autonomy still require a human driver onboard ready to take over. Finally, Level 4 defines a car that can drive itself over an entire trip, with a human occupant only selecting a destination.

2016 Tesla Model S

Musk believes Tesla can achieve this eventually, and in the meantime the company is working to improve Autopilot. Engineers currently download data from customer cars to see how the system behaves in the real world. They also use special software to run simulations of new Autopilot features on customers cars as those cars travel down the road.