What You Need to Know About the Types of 'Self-Driving' Cars

— -- This morning’s announcement that Uber has introduced a new fleet of “self-driving” cars to shuttle passengers around Pittsburgh may have consumers wondering exactly what that means.

However, not all "self-driving" cars are the same -- the U.S. National Highway Traffic Safety Administration classifies vehicle autonomy into five categories, ranging from Level 0 to Level 4.

If you've used a car, your vehicle is probably between Levels 0 and 2.

According to the NHTSA, drivers of Level 0 cars have “complete and sole control of the primary vehicle controls -- brake, steering, throttle, and motive power -- at all times.”

Level 0 cars are the most basic on the road, with nothing like cruise control or assisted braking.

The next level up, includes cars with “one or more specific control functions,” according to the NHTSA. This can include things like stability control or pre-charged brakes, which provide some assistance to drivers.

Level 2 cars have “at least two primary control functions,” that are autonomous, which according to the NHTSA, include things like adaptive cruise control -- cruise control systems that, through sensors, maintain a safe distances from other vehicles.

While Level 2 may sound run-of-the-mill, much of the buzzworthy work in self-driving vehicles is still happening at Level 2.

Tesla’s “AutoPilot” systems, which allow certain models to maintain or even switch lanes and control and adjust speed based on the presence of other cars, is Level 2.

Then there is Level 3, which is the level that Uber’s Pittsburgh cars are operating at.

According to the NHTSA, Level 3 vehicles “enable the driver to cede full control of all safety-critical functions under certain traffic or environmental conditions,” while the driver is still “expected to be available for occasional control, but with sufficiently comfortable transition time.”

Level 4, the highest level, is probably what most people think of when it comes to self-driving cars.

While Level 4 autonomous vehicles expect a human to input a destination, humans are not “expected to be available for control at any time during the trip.” Level 4 vehicles could also be operated without drivers, according to the NHTSA.

There are other classifications for self-driving cars. SAE International, a society of engineers, has its own 6-level ranking system. However, both Tesla and Uber user the NHTSA's system in discussing their vehicles.

ABC News’ Jeffrey Cook contributed to this report from Washington.