What is a self-driving car?

Chevrolet Bolt EV self-driving prototype

Chevrolet Bolt EV self-driving prototype

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Self-driving cars are a popular topic in both the auto industry and general media coverage these days, with several makers testing vehicles and promising fully autonomous cars at some future point.

But when it comes to self-driving cars, different automakers may not be talking about the same thing.

Some vehicles on sale today offer driver-assistance systems that take over certain driving functions on a limited basis.

Those are a far cry from systems that can pilot a vehicle from point to point with no human intervention at all.

DON'T MISS: GM releases second Chevy Bolt EV autonomous driving video

They represent a transitional stage between fully manual driving and a time many in the auto industry insist will come: when at least some people will not drive themselves at all.

To help clarify things, this guide is based on the levels of autonomy—Level 0 to Level 5—that was defined by the Society of Automotive Engineers in 2014.

Keep in mind that while automakers may discuss "fully-autonomous" or "Level 5" features, vehicles with that degree of autonomy are not legal on most public roads in the U.S.

Moreover, laws in the areas where they are allowed on public roads explicitly permit only tests, not consumer sales.

SAE levels of autonomy

SAE levels of autonomy

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With that, here is our primer on the levels of autonomy.

Level 0: No self-driving capabilities. Drivers are responsible for controlling steering, throttle, and braking, as well as monitoring their surroundings.

Most cars on the road today fall into this category, even those equipped with some assistance features like blind-spot monitoring and forward-collision warning.

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Level 1: Some driver assistance. Cars can take control of the steering or the throttle/brake in certain situations, but rely on the driver to immediately take over if those systems fail.

Vehicles equipped with adaptive cruise control, autonomous emergency braking, and lane-departure prevention fall into this category.

Level 2: More driver assistance. Like Level 1, cars rely on a human driver to take over if autonomous systems fail or are out of their depth.

However, the extent of autonomous functionality is greater, including being able to control steering and the throttle and brakes simultaneously.

These systems cannot perform specific tasks, such as highway merging or navigating stop-and-go traffic.

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