To help understand the evolution of technology between traditional cars and fully autonomous vehicles, SAE International (born the Society of Automotive Engineers) has come up with a scale to describe the different levels of automation. The National Highway Traffic Safety Administration—the U.S. auto-safety regulator—has now adopted the same scale, creating a common vocabulary to explain this emerging technology. These levels of automation have become the shorthand that all of the companies in the field use to describe their progress.

Below is a cheat sheet on how we'll get from the advanced cars of today to the self-driving cars that may rule the roads in the future. 

Level 1: Driver Assistance

This describes many of today’s new cars. The human driver is responsible for the safety and operation at all times, but the car can take over at least one vital function: steering or speed control. Adaptive cruise control is the best example of existing technology at this level.

Level 2: Partial Automation

Today’s more advanced cars qualify as Level 2. The driver is still responsible for the safe operation of the vehicle, but it can take over steering, braking, and acceleration under certain conditions. The driver is expected to do everything else and monitor road conditions. Tesla’s Autopilot and similar systems from Mercedes-Benz, BMW, and Volvo are good examples of partial automation.

Level 3: Conditional Automation

The car can drive itself, but the human driver must still pay attention and take over at any time. The car is supposed to notify its driver if intervention is needed. This may be the most difficult level to manage because experiments have shown people tend to put too much trust in the technology and stop paying attention.

Level 4: High Automation

Here, the human driver has handed over control to the computer driver under certain situations, such as highway driving or set routes or areas. The human driver does not need to pay attention until the car asks him to. The car is expected to have backup systems so that if one technology fails, it will still be operational. If the car determines it’s not safe to continue, it will pull over and shut down. Automakers predict this type of car will become available, probably as part of ride-sharing or taxi fleets, in the next few years.

Level 5: Full Automation

The car controls itself under all circumstances, in all the places a human could drive, with no expectation of human intervention. These cars won’t need steering wheels, brake pedals, or accelerators. This level would open up vast opportunities for people who can’t drive today, such as the blind, the disabled, and kids.

Editor's Note: This article also appeared in the April 2017 issue of Consumer Reports magazine.