About Levels of Driving Automation


From cruise control to driverless, Tom takes a tour of the levels of driving automation.

Featuring Tom Merritt.



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I keep hearing about self-driving cars
Some are on Autopilot but others have reached level 5 or something?
Is that a video game? Are self-driving cars rated on video game playing?
Don’t be Let’s help you know a little more about Levels of Driving Automation.

Autonomous cars are cars that can drive themselves. But some can drive themselves more than others. So over the years organizations have tried to define levels of autonomy so you know just how autonomous and reliable a car’s self-driving capabilities are.
There have been different definitions over the years and of course every car manufacturer has its own brand names on top of these.
But the good news is that in the last few years the Society of Automotive Engineers or SAE has published Levels of Driving Automation that have become the standard that all the brand names and shortcuts refer back to.
SAE J3016™ Recommended Practice: Taxonomy and Definitions for Terms Related to Driving Automation Systems for On-Road Motor Vehicles was launched in 2014 but you can call it SAE Level of Driving Automation for short. It occasionally gets refined and clarified but it generally is holding up as the easy way to signal how capable an autonomous driving feature is. The most recent revision is J3016_202104 released in April 2021.
There are 5 levels, well 6 if you count Level 0. Let’s go through them here with a rough (and engineers please bear with me as I oversimplify a little here and there) I say again rough explanation of what each level means.
Level 0 is the easiest. It’s manual. No automation. Though we don’t mean a stick shift from the 1960s. It can still have advanced features. The car may tell you things or even do a few things but it doesn’t do any driving. So blind spot warning, lane departure warning, these are are still cool under level 0. In fact even automatic emergency braking is still level 0 according to SAE’s graphic on this. These are momentary warnings and brief assistance. The level 0 features have no sustained control over the car.
Level 1 can do some more sustained assistance. So lane centering brings a car up to level 1 since its adjusting the steering on an ongoing basis. Cruise control counts here because it can speed up and slow the car for you. You’re still steering or braking the car but the car can jump and help with these– one at a time. It can center you in the lane. It can maintain speed with cruise control. But here’s a key, it doesn’t do both at the same time. Parking assistance is level 1 because it only steers while you control the speed.
These first two levels are defined as Assistance. Level 2 is the first one that uses the word Automation and that’s because it can do more than one thing at a time. If the car can maintain cruising speed AND Center you in the lane that’s level 2. That’s because it can steer accelerate and brake when it needs to. It’s not just monitoring one thing. So SAE kind of considers that doing a little bit of driving for you. This level is confusingly called Hands off or Autopilot sometimes but it’s really neither. One key to level 2 is the driver is always responsible. The system is not considered reliable enough to operate unsupervised.
Level 3 is the first one where you can relax (sometimes) and not have to supervise to maintain safety (sometimes). With Level 3, under limited conditions, the car can drive itself. However one of the things that makes it level 3 is that even if the conditions are met it can’t always drive itself, so you have to be ready to take over. There still needs to be human in the driver seat with a steering wheel and pedals. A common example of this is traffic jam driving. On a controlled access highway the car can speed up and slow down as needed to keep you moving through traffic. It is considered reliable enough that you don’t need to pay full attention. But at certain times, like maybe after you get off the highway, the human driver may have to take over. One important thing about Level 3 is it doesn’t mean you can fully take your eyes off the road. But maybe now you could take your hands off the steering wheel.
Level 4 is real autonomous driving. If certain conditions are met, the car can drive itself and it will not operate if those conditions aren’t met. A good example here is an autonomous taxi service in a predefined and well mapped region. Within that region the taxi doesn’t need a human driving it, and it won’t operate outside the region. This is the first level where you might have a car without a steering wheel and a pedal. It can’t drive everywhere. It’s not a general purpose vehicle. But within it’s parameters it can go without needing a human driving. Outside it’s parameters it can safely pull to the side of the road and stop for instance.
Level 5 is the holy grail that some people say we may never actually achieve. Level 5 means a vehicle can drive reliably and safely everywhere under all conditions in which a human can drive now. I can’t drive in a blinding blizzard so no the Level 5 system won’t either. But it doesn’t need predefined regions or special conditions and it doesn’t need a human or a steering wheel or pedals.
Let’s go back over those last few again. Level 3 means the human doesn’t always have to supervise. The car however may tell you to take back control so you need to be ready to do that. The driver is not relieved of all responsibility. Level 4 means the human does not have any responsibility anymore. The car will just stop itself if it meets conditions it can’t drive in. And Level 5 can drive pretty much anywhere in any condition a human could and doesn’t need a human to do it.
Right now most cars that you can buy have level 2 features or lower. Even those with traffic jam assistance and lane keeping assistance are usually not reliable enough for the human to be relieved of the responsibility of having their hands on the wheel. Level 3 vehicles do exist though. Mercedes-Benz and Honda were the first two manufacturers to get regulatory approval for level 3 services. Honda got it for its Traffic Jam Pilot in Japan in November 2021 and Mercedes got it in Germany for Automated Lane Keeping that it calls Drive Pilot in December 2021.
Level 4 systems are limited to tests with certain buses in limited commercial parks and some small suburban routes by Waymo vehicles. And Level 5 doesn’t exist yet.
A few more things to keep in mind regarding these definitions. They are designed to describe the level of human interaction and capability of the system to drive on roads. They aren’t a measure of value or quality. A really tricked out Level 0 car may be a better car than a really minimal Level 4 bus.
And they’re not measures of safety. Level 2 is a big minefield for this. There are loads of arguments about how safe the implementations of Tesla’s Level 2 features are. SAE levels don’t have anything to say about that.
It’s also worth pointing out that the Levels are meant to apply to features not cars. The driver assistance may be Level 3 but that doesn’t make the car Level 3 overall. It may only have Level 0 for all its other features. That might seem like a distinction without a difference but you might find it useful if you found yourself shopping for a car with Level 3 features. That Mercedes Automated Lane Keeping is Level 3 up to 37 miles per hour on designated highways in Germany. The rest of the time it’s not a level 3 car.
And finally if you see Level 2.5 or Level 2+ those are actually prohibited by the SAE. So they’re just marketing terms, not official designations.
But with all these caveats the levels are useful and used often to delineate just how capable a car’s features and systems are. So hopefully it’s helpful that now, you know a little more about Levels of Driving Automation.