Self-driving cars are one of the hottest topics in the world of tech right now, and it’s not hard to see why. For as much as people romanticize driving, it can be a monotonous, tiring activity, and even good drivers can make mistakes that end in gruesome accidents. If cars can drive themselves and use advanced tech to avoid accidents entirely, wouldn’t that be nice?

Automation isn’t a binary concept, however, it’s a spectrum, with varying degrees as humans hand over responsibilities to the machine.

The society of Automotive Engineers created an international standard for measuring the degrees of automation in cars, called J3016.

The scale runs from 0 to 5, with 0 being no automation (so, good old-fashioned cars like the Model T or ‘70s sports cars). From levels 1 to 2, the person in the driver’s seat has to, at the very least, supervise the car, even if they’re using support features to steer or maintain acceleration. For example, cruise control can keep a car going at a constant speed without the driver needing to think about maintaining speed, but the driver is still in control of the car, and

Once you get to levels 3-5, the car can drive itself (for levels 3 and 4, only under certain predetermined conditions).

SAE takes into account whether features added to a car are “driver support” features, that might make it easier to brake, but still leave the act of driving to the driver.

Level 2 cars can use cameras, ultrasonic sensors, RADAR and LIDAR to scan surroundings, then uses artificial intelligence to determine whether something is a distinct object, whether it’s a human or another car, and so on. These “self-driving” cars still are far from perfect, however, and sometimes have trouble recognizing objects.

Automation could improve shipping, making it so cross country trucker no longer need to focus on driving during the long, empty stretches of highway they spend much of their time on. Trucking companies are investing in this tech, eager to reduce the risk of costly accidents.

At level 3, the car is using “conditional automation.” At this level, the car can drive itself in many conditions, and doesn’t need the human driver to monitor, although it will, in certain conditions, request the driver take the wheel.

At level 4, the car can drive in most conditions and won’t even need the human to intervene. Level 5 is much the same, but the car can drive in basically any conditions.