July 18, 2024
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The 5 levels of autonomous driving explained

If you've been keeping up with the news about autonomous vehicles, or just spent a little time in our Cars Category: You've probably seen people use terms like “Level 2 autonomy” or “Level 4 autonomous driving.” But what do these levels mean and how do they work in the real world? In this explanation, we break down the five levels of vehicle autonomy.

What is autonomous driving?

“Autonomous driving” refers to the ability of a vehicle to perform some driving tasks independently. These tasks vary greatly; As a result, some types of autonomous driving are much more useful than others. To describe the capability of each degree of autonomy, the autonomous driving capabilities of vehicles are divided into five levels. For this, you can thank SAE International (formerly known as the Society of Automotive Engineers), which developed this five-level taxonomy in the late 2010s. Since then, the organization's taxonomy has been updated to accommodate the language and audience of the 2020s, but the principle remains the same.

Infographic from SAE International showing the five levels of autonomous driving.

Credit: SAE International

The terms “autonomous driving” and “autonomous driving” are often used interchangeably, but “autonomous driving” tends to invoke a higher level of capability, such as that found in levels 3 to 5. What is each of them like? those levels? We'll see.

Level 1 autonomous driving

Level 1 is the lowest of the autonomy levels, unless you count level 0, which describes a vehicle without autonomous features. But there's not much more to say about Level 0, so we'll start with Level 1.

This level is often called “driver assistance.” This is because the tasks automated by Level 1 make the driver's job a little easier, but are not important enough to reasonably be considered “autonomous driving.” You may already drive a vehicle with Level 1 autonomy.

Vehicles classified in Level 1 incorporate functions 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 leaving its current lane. They might also be able to perform automatic emergency braking when a pedestrian, a stray shopping cart, or other obstacle suddenly appears. These features require visual information from built-in cameras and infrared sensors, often located at the front of the car, in the rearview mirrors, or at the rear of the vehicle.

A vehicle traveling in the far right lane that borders 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 a wrong lane change. Similarly, the National Highway Traffic Safety Administration says More than 24,000 accidents could be avoided annually in the United States alone if all light passenger vehicles had automatic emergency braking functions.

But even when Level 1 functions are activated, it is imperative that the driver maintain control over the car and pay close attention to their surroundings. Vehicles with Level 1 autonomy are not even remotely capable of letting the driver off the hook. SAE International includes the “human driver” in all driving-related tasks in its five-level chart.

Level 2 autonomous driving

Level 2, sometimes called “partial automation,” takes Level 1 to a higher level. A human driver is still required to keep a close eye on the road (no naps allowed during rush hour!), but the most essential driving tasks are automated. Adaptive cruise control, lane assist, and automatic emergency braking features are still included. But they are accompanied by hands-free steering, traffic sign recognition, blind spot detection and automatic parking. As with Level 1, these functions are made possible by cameras, infrared sensors and ultrasound. Some Level 2 vehicles even offer night vision, which takes advantage of 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 is known as an advanced driver assistance system or ADAS. Some ADAS can only be used in specific circumstances, such as Audi's Traffic Jam Assist, which offers hands-free steering at speeds below 40 miles per hour. Tesla's Full Self-Driving and Cadillac Super Cruise were two of the first systems to enter Level 2 autonomy. Many vehicles manufactured in the last year have some type of ADAS, starting in 2022. Ford F-150 Lightning to the Rivian R1T and R1S 2022.

Level 3 autonomous driving

Level 3, or “conditional automation,” is where we start to see capabilities that match our general colloquial understanding of the term “autonomous driving.” In vehicles classified as Level 3, the driver may not intervene if appropriate environmental conditions are met. This warning means that the driver must remain prepared to intervene if the self-driving software forces them to do so.

In practice, Level 3 autonomy allows a vehicle to accelerate, brake, turn, park, follow signs and traffic signals, enter and exit a highway, and maintain a safe speed and distance from other vehicles – that is, all tasks you normally perform when driving a car yourself. Through a complex network of sensors, processors and algorithms, Level 3 vehicles can “make their own decisions,” allowing them to manage much of the driving experience. Certain circumstances, such as complex construction zones, accident sites, or other scenarios, may require a driver to intervene.

A Mercedes sedan with the "Interior driving light" 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 greatly desired for himself. Mercedes started selling Drive Pilot-equipped cars in April 2024. After watching an instructional video, drivers of 2024 S-Class and EQS sedans can sit back and enjoy their vehicles' infotainment systems without sacrificing their safety or the safety of others. Naps still However, this will not be allowed, as Mercedes' Drive Pilot software will need to be able to “see” the drivers' eyes at all times. So while Level 3 is a leap in technology, in practice, it's more of a benchmark toward Level 4.

Level 4 autonomous driving

This is where things get more exciting. Also called “high automation,” Level 4 reduces the responsibility of the human driver until it is almost completely unnecessary. Level 4 vehicles are better equipped to handle the problematic circumstances we mentioned above, thus eliminating the need for a driver to intervene, but drivers can take charge if they wish.

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

A Waymo minivan parked on the side of the road.

Credit: Waymo

As for individual drivers, Level 4 autonomy promises a more relaxed experience. The idea is that a daily commute or long road trip will be more enjoyable when the driver can read a book, watch Netflix on their vehicle's infotainment screen, or even take a nap. But for commercial use, Level 4 offers a way to reduce driver fatigue, improve safety and reduce costs.

“Autonomous vehicles can operate continuously to help alleviate supply chain issues, reduce the impact currently felt by the global driver shortage, and reduce fuel consumption by 10% relative to manually driven trucks.” Lu said. “This all equates to operators seeing lower costs when transporting goods with an autonomous vehicle.

tesla expected to reach your version of Level 4—controversially called Fully Autonomous Driving, by the end of 2023, although that date has come and gone.

Level 5 autonomous driving

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

A woman using her laptop behind the wheel.

Credit: ThisIsEngineering/Unsplash

Currently, Level 5 is the stuff of dreams. Since only a few companies have mastered Level 4 driving (and those vehicles are not available to consumers), it doesn't make sense to make the jump to Level 5 yet. “In theory, a Level 5 vehicle can operate anywhere,” Lu said. “That means that this vehicle should be able to be 'dropped off' in any country or city, and should be able to be driven without problems. We are not currently seeing that.”

What is the “correct” level of autonomy?

Autonomous vehicles (and the many forms they take) are not a one-size-fits-all solution. We are just a short time away from vehicles across the SAE International spectrum being available to consumers. Still, when that day comes, your specific needs will tell you what level of autonomy best suits you.

“If the purpose is to assist the driver and improve safety and comfort, then (an) ADAS L2 would be sufficient,” Lu told ExtremeTech. “If the goal is to get the driver out of the vehicle and unlock additional benefits including increased safety, increased 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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