The 5 Levels of Autonomous Driving Explained

The 5 Levels of Autonomous Driving Explained


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If you’ve been keeping up with autonomous vehicle news—or just spending a bit of time in our Cars category—you’ve probably seen people throw around terms like “Level 2 autonomy” or “Level 4 self-driving.” But what do these levels mean, and how do they work in the real world? In this explainer, we break down the five levels of vehicular autonomy. 

What Is Autonomous Driving?

“Autonomous driving” refers to a vehicle’s ability to perform some driving tasks independently. These tasks vary greatly; as a result, some types of autonomous driving are far more helpful than others. To describe how capable each degree of autonomy is, vehicles’ self-driving capabilities are divided into five levels. For this, you can thank SAE International (previously known as the Society of Automotive Engineers), which developed this five-level taxonomy in the late 2010s. The organization’s taxonomy has since been updated to suit the language and audience of the 2020s, but the principle remains the same. 

SAE International infographic displaying the five levels of autonomous driving.

Credit: SAE International

The terms “autonomous driving” and “self-driving” are often used interchangeably, but “self-driving” tends to invoke a higher level of capability, like that found in Levels 3 through 5. What do each of those levels look like? Let’s take a look.

Level 1 Autonomous Driving

Level 1 is the lowest of the autonomy levels—unless you count Level 0, which describes a vehicle without autonomous traits. But there isn’t much else to say about Level 0, so we’ll start with Level 1.

This level is often referred to as “driver assistance.” This is because the tasks automated by Level 1 make the driver’s job slightly easier but aren’t significant enough to be reasonably considered “self-driving.” You might drive a vehicle with Level 1 autonomy already.

Vehicles categorized under Level 1 incorporate features such as adaptive cruise control, which adjusts the vehicle’s speed to that of the car in front of it, or lane assist, which prevents the vehicle from drifting out of its current lane. They might also be capable of automatic emergency braking when a pedestrian, stray shopping cart, or other obstacle suddenly appears. These features require visual input from built-in cameras and infrared sensors, often located toward the front of the car, in the rearview mirrors, or at the back of the vehicle. 

A vehicle driving down the far-right lane along the coast.

Credit: Cristofer Maximilian/Unsplash

Level 1 lane assist features have been shown to prevent up to 11% of traffic accidents that would have occurred due to an erroneous lane departure. Similarly, the National Highway Traffic Safety Administration says more than 24,000 crashes would be prevented annually in the United States alone if all light passenger vehicles possessed automatic emergency braking features.

But even when Level 1 features are engaged, it’s imperative that the driver maintains control over the car and pays close attention to their surroundings. Vehicles with Level 1 autonomy aren’t anywhere near capable of letting the driver off the hook. SAE International lists “human driver” under all driving-related tasks in its five-level chart. 

Level 2 Autonomous Driving

Level 2, sometimes called “partial automation,” takes Level 1 up a notch. A human driver is still required to keep a close eye on the road (no rush hour naps allowed!), but more essential driving tasks are automated. The adaptive cruise control, lane assist, and automatic emergency braking features are still included. But they’re accompanied by hands-free steering, traffic sign recognition, blind spot detection, and automated parking. As with Level 1, these features are made possible through cameras, infrared sensors, and ultrasound. Some Level 2 vehicles even offer night vision, which leverages thermal imaging to see people or things that would otherwise be hidden in the dark. 

The interior of a car stuck in traffic.

Credit: Dan Gold/Unsplash

In many Level 2 vehicles, these features are packaged together in what’s known as an advanced driver assistance system, or ADAS. Some ADAS can only be used under specific circumstances, like Audi’s Traffic Jam Assist, which offers hands-free steering at speeds under 40 miles per hour. Tesla’s Full Self-Driving and Cadillac Super Cruise were two of the first systems to fall under Level 2 autonomy. Many vehicles manufactured within the last year or so boast some form of ADAS, from the 2022 Ford F-150 Lightning to the 2022 Rivian R1T and R1S. 

Level 3 Autonomous Driving

Level 3, or “conditional automation,” is where we begin to see capabilities that match our general colloquial understanding of the term “self-driving.” In vehicles categorized under Level 3, the driver can be hands-off if the proper environmental conditions are met. This caveat means the driver needs to remain ready to intervene should the self-driving software compel them to.

In practice, Level 3 autonomy enables a vehicle to accelerate, brake, steer, park, navigate traffic signs and signals, enter and exit a freeway, and maintain a safe speed and distance from other vehicles—AKA all of the tasks you typically do when you’re driving a car yourself. Through a complex web of sensors, processors, and algorithms, Level 3 vehicles can ” make their own decisions,” allowing them to manage much of the driving experience. Certain circumstances, like complex construction zones, crash sites, or other scenarios, might require a driver to intervene. 

A Mercedes sedan with the "Drive Pilot Inside" graphic on the side.

Credit: Mercedes-Benz

Mercedes-Benz made headlines earlier this summer after becoming the first automaker to secure Level 3 approval in California—an honor Tesla very much wanted for itself. Mercedes began selling Drive Pilot-equipped cars in April 2024. After watching an instructional video, those who drive 2024 S-Class and EQS sedans can sit back and enjoy their vehicles’ infotainment systems without sacrificing their safety or anyone else’s. Naps still won’t be allowed, though, as Mercedes’ Drive Pilot software will need to be able to “see” drivers’ eyes at all times. So, although Level 3 is a jump in technology, practically speaking, it’s more of a waypoint to Level 4.

Level 4 Autonomous Driving

This is where things get more exciting. Also called “high automation,” Level 4 reduces the human driver’s responsibility until they’re almost entirely unneeded. Level 4 vehicles are better equipped to manage the problematic circumstances we mentioned earlier, thus eliminating the need for a driver to intervene—but drivers can take over if they wish. 

“Level 3 enables autonomous driving only in certain conditions and situations,” Cheng Lu, CEO of the autonomous trucking company TuSimple, told ExtremeTech. “With Level 3, the driver must be present and alert at all times during the drive to take over in extreme situations.” But in situations where a Level 4 vehicle has an operational design domain (ODD), a driver might not be required, making what Lu calls “driver-out runs” possible. This includes TuSimple’s own automated truck routes, and Waymo’s relatively small self-driving taxi runs. 

A Waymo minivan parked on the side of the road.

Credit: Waymo

Regarding individual drivers, Level 4 autonomy promises a more relaxed experience. The idea is that a daily commute or long road trip will become more pleasurable when the driver can read a book, watch Netflix on their vehicle’s infotainment screen, or even snooze. But, regarding commercial use, Level 4 offers a way to reduce driver fatigue, improve safety, and reduce costs.

“Autonomous vehicles can operate continuously to help ease supply chain issues, lower the impact currently being felt [from] global driver shortages, and reduce fuel consumption by 10% relative to manually driven trucks,” Lu said. “All of this equates to operators seeing lower costs when running freight with an autonomous vehicle.

Tesla hoped to achieve its version of Level 4—controversially called Full Self-Driving—by the end of 2023, although that date came and went.

Level 5 Autonomous Driving

Level 5 automation, or “full automation,” makes a vehicle capable of driving itself under any circumstances. A human driver is entirely unnecessary, regardless of the weird situations the vehicle encounters.

A woman using her laptop behind the steering wheel.

Credit: ThisIsEngineering/Unsplash

Currently, Level 5 is the stuff of dreams. With only a few companies having mastered Level 4 driving—and those vehicles being unavailable to consumers—it doesn’t make sense to leapfrog to Level 5 just yet. “Theoretically, a Level 5 vehicle can operate anywhere,” Lu said. “That means you should be able to ‘drop’ this vehicle in any country or city, and it should be able to drive flawlessly. We currently aren’t seeing that.”

What’s the ‘Right’ Level of Autonomy?

Autonomous vehicles—and the many forms they take—aren’t a one-size-fits-all solution. We’re a while away from vehicles across the SAE International spectrum being available to consumers. Still, if or when that day comes, your specific needs will tell you which level of autonomy fits best.

“If the purpose is to support the driver and improve safety and comfort, then [an] L2 ADAS would be sufficient,” Lu told ExtremeTech. “If the goal is to remove the driver from the vehicle and unlock additional benefits including improved safety, better fuel efficiency, and lower costs, then Level 4 or Level 5 is required.”

For more, read How Do Electric Cars Work? A Basic Primer.

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