A view of the dashboard of a Cadillac on the highway: The driver's hands are off of the steering wheel.

GM's new Super Cruise system is an example of a "conditional" automated-driving system. Image source: General Motors.

Often, in articles about self-driving cars or autonomous-vehicle systems, you'll see references to "levels"  -- Level 4, Level 5, and so on. What do those levels refer to? I'm glad you asked.

The six levels of automated driving 

The levels are a shorthand way to describe the amount of automation (versus human control) provided by a particular automotive system. The levels follow definitions set out a few years back by SAE International, the professional association of automotive engineers that sets many technical standards followed by automakers around the world. 

Until fairly recently, there were a few different ways of categorizing vehicle-automation systems. Now, just about everyone -- automakers, technology companies, and even regulators -- have adopted the SAE's broad definitions. 

The SAE defines six levels of vehicle automation, from Level 0 to Level 5:

  • Level 0 is no automation: The human driver is responsible for all aspects of what the SAE refers to as "the dynamic driving task," meaning the actions taken to control the vehicle. There may be systems that help the driver, and even something that intervenes in a very specific situation (like an automated emergency braking system), but they don't count as "automation" because they don't do any part of the "dynamic driving task" on a sustained basis. 
  • Level 1 is a driver-assistance system that provides either steering or acceleration-and-braking control that is sustained but only under limited, specific circumstances. Adaptive cruise control systems are considered Level 1: The system controls acceleration and braking to keep the vehicle at a set distance behind another car on the highway, but the human driver is still responsible for all other aspects of driving. 
  • Level 2 is a driver-assistance system that provides both steering and acceleration-and-braking control, again under limited circumstances. This still isn't quite self-driving, because the expectation is that the human driver will need to intervene regularly. Tesla's (NASDAQ:TSLA) original Autopilot was considered a Level 2 system, albeit an advanced one.
  • Level 3 is where we start to get into actual automation of the driving task. It's "conditional automation," meaning that the system is only able to operate under some conditions -- but when it's operating, it's self-driving. General Motors' (NYSE:GM) new Super Cruise system edges into Level 3 territory, as do the latest versions of Tesla's Autopilot. The difference from Level 2 is one of degree: The human driver typically won't have to intervene when the system is operating, but he or she will still need to maintain some awareness in case the system signals a need for the human to take over.
  • Level 4 is considered "high automation." Generally, we use Level 4 to describe a system that really is fully self-driving, with no human intervention needed -- but only under some circumstances. A self-driving system that relies on special maps to work (as most systems currently under development do) would be considered Level 4: It's fully self-driving with no human intervention needed anywhere it has a map, but it's not self-driving everywhere.
  • Level 5 is full automation: The system can drive the vehicle in any circumstances a human could. It can go anywhere there are passable roads, with no human driver needed at any time. 

How the industry views the automated driving levels

Level 2 and Level 3 systems are considered a bit risky by some experts. The challenges with those systems arise when the system urgently needs the human to take over: If the human is distracted, it may take several seconds for her or him to focus on the situation and take control of the car. That issue has led some automakers, including Ford Motor Company (NYSE:F), to skip over Level 3 and work toward a full Level 4 system instead. 

When we talk about the self-driving systems that are likely to begin coming to market (in some way) over the next few years, we're mostly talking about Level 4 systems. Those systems will be genuine self-driving, but they'll be limited by their maps and possibly in their ability to operate in (for instance) extreme weather conditions like ice and snow. 

Most experts think that full-blown Level 5 systems are still many years away. But as with everything having to do with technology, there's always a possibility that advancements will happen more quickly than the experts predict. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.