Driving automation: The five levels of autonomy

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It would be a cultural revolution if cars could actually drive autonomously. Either optionally, i.e. at the push of a button and on demand, or as so-called robotaxis without a steering wheel and pedals: If this were possible, coexistence in cities and the countryside would change radically. Road traffic would probably be safer than today. The tedious commute could become a sightseeing tour. People with mobility impairments could get to the supermarket or doctor more easily. Staff shortages in the logistics industry would also be a thing of the past. There is much to suggest that this vision will become reality at some point in the 2030s. The current state is comparatively simple: most new cars have a Level 2 driving automation system and are partially automated. In the first part of this series, we clarify some basic terms.

No clear designation, but conventions

A jumble of designations has established itself in the description of the systems, which are not legally regulated and are not even used consistently in the professional world. But there are conventions, i.e. agreements and rules, that have become established internationally. The five levels of driving automation are the best known. Developers first distinguish between longitudinal and lateral control: Longitudinal control means acceleration and deceleration as well as braking. “Lateral control” refers to steering. Some of the almost 50 million passenger cars in German stock support the driver in neither. Driver Only is the jargon for this. The human does everything. It couldn't be clearer: that's Level 0.

Level 1 is already assisted. There are aids such as an anti-lock braking system for steering control during braking, ESP to prevent skidding, and acoustic and visual symbols for parking. A cruise control system that changes the distance to the vehicle in front (abbreviated ACC for Adaptive Cruise Control) also belongs to Level 1, as long as the steering task is performed by the human. The decisive factor for this classification is that the car supports either longitudinal or lateral control.

Standard: Combination of longitudinal and lateral control

If the person at the wheel is assisted in both longitudinal and lateral control, it is a Level 2 system, which is called partially automated in technical jargon. Typical for this application is the combination of adaptive cruise control (ACC) and lane centering: The vehicle brakes and accelerates, perhaps it also recognizes traffic signs and adopts the speed limit into the ACC. In addition, it steers into the center between the lane markings, whereby the steering support should be cooperatively designed: This means that the human can make slight corrections without the system immediately switching off. This can be the case, for example, in construction sites with yellow and white lines.

Level 2 systems can be ordered in new cars, even in most small cars, or are even standard. However, it is fundamentally important to understand that the function of assistance systems for longitudinal and lateral control must be continuously monitored. To ensure that the human is attentive, they are checked by hands-off detection: the hands must be on the steering wheel, which is detected by steering torque in older designs. In modern vehicles, capacitive steering wheels determine whether the hand is on the steering wheel.

To monitor the driver's presence, cameras are also increasingly being used, which work with eyetracking, among other things. These systems can sometimes be quite intrusive, for example, if a sideways glance is sufficient to detect a supposed distraction. In any case, the car driver is continuously responsible with the currently common Level 2 systems and cannot hand over the driving task.

Extended Level 2 systems

This is foreseeable becoming a problem because Level 2 systems are getting better and better. Beyond the current nomenclature used by the US SAE (Society of Automobile Engineers) and the German VDA (German Association of the Automotive Industry), among others, there are further developments of Level 2 called Level 2+ or Level 2++. In Level 2+, the driver's attention is no longer checked via hands-off detection but via a camera: the person sits in the driver's seat and essentially watches the car steer, brake, and accelerate. They don't have to keep their hands on the steering wheel. Level 2++ goes one step further. Here, the car appears to drive autonomously from start to destination. However, it can make mistakes and must therefore be continuously monitored as before. Tesla FSD or Mercedes MB.Drive Assist Pro Drive Assist Pro are examples of this. Such systems are already approved in China and the USA.

For Europe, regulation is not expected before 2027, but it is coming. Among other things, the driver must understand what their role is, i.e. that they must always pay attention if the Level 2++ system makes a mistake. If they don't grasp this, it's called “mode confusion.” This is feared because it can be dangerous. More about the potential and risks of extending Level 2 can be read in the third part of this series on driving automation.

The other quality after Level 2

With Level 3, highly automated driving, a different quality begins for the first time: the person at the wheel is allowed to completely withdraw from the driving task in at least one defined situation – for example, during the day on a dry highway – to play with their smartphone or eat a roll. However, they must be able to retake control within a period of, for example, ten seconds if the car recognizes system limits. Currently, only two car types are approved for Level 3: the Mercedes EQS and the BMW 7 Series; at the recently revised S-Class, it is paused according to Mercedes.

To guarantee safety, sensor technology and control are designed redundantly. Nevertheless, these Level 3 systems have narrow limits and fail at night, in bad weather, or at higher speeds. A manufacturer can freely determine the exact conditions under which such a system functions. Of course, they can also offer this functionality in more than one scenario.

Perhaps the industry will forgo further development of Level 3 and switch directly to Level 4, fully automated driving. Here, the system can handle all driving tasks itself within at least one specific use case. Unlike Level 3, the ability to retake control is not necessary in this scenario. This also explicitly applies here: manufacturers can offer this for various use cases. Level 5 differs only in the ability to drive off paved roads and without a driver.

Reduction of term diversity

The subtle linguistic distinctions between the levels and the confusion, which affects not only laypeople, have led to a reorganization at the Federal Institute for Road and Transport (BASt). The BASt is streamlining and reducing the terms. According to the proposals of the BASt, there should only be three levels:

• Assisted driving, where the human must monitor the functions. It corresponds to the previous Levels 0 to 2.
• Automated driving, where the human may turn away from the driving task in a defined situation but must be able to retake control. This is the previous Level 3.
• Autonomous driving. Here, the BASt combines the previous Levels 4 and 5, which were never particularly sharply or clearly defined anyway.

But what if something goes wrong and an accident occurs? We explain this in the second part of this series.

(vbr)