Levels of Autonomous Driving, Explained

As self-driving vehicles move from science fiction to reality, automakers are poised to make key advancements in this area over the next five to 10 years. But vehicle autonomy can potentially mean many things and have many implications. To set agreed-upon standards early in the transition to autonomous vehicles, the Society of Automotive Engineers (SAE) developed a classification system which defines the degree of autonomy by which a vehicle operates. Ranging from levels zero to five, the driving automation spectrum begins with manually controlled vehicles and ends with completely driverless chariots.

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Level 0 – No Automation

Level 0 refers to a vehicle that has no driving automation. In this case, the driver is fully in charge of operating the movement of the vehicle. That includes steering, accelerating, braking, parking, and any other necessary maneuver to pilot the car. However, the driving experience can include intervening systems such as automatic emergency braking, blind-spot warning, and lane-departure warning. These technologies do not drive the vehicle but offer proper alerts or guidance in specific situations. A majority of vehicles on American roadways are Level 0.

Level 1 Automation – Driver Supervised Steering OR Acceleration and Braking Assistance

At Level 1, the lowest rung of automation, the driver is responsible for most of the required driving tasks of the vehicle, in combination with just one driving assistance feature that impacts the movement of the vehicle in a specific way. Adaptive cruise control is an example, which maintains a safe distance between your vehicle and traffic ahead. A steering assistance feature that helps a vehicle stay in its lane would also qualify as Level 1 autonomy. A vehicle with both of these features qualifies for Level 2 automation.

Level 2 Automation – Driver Supervised Steering AND Acceleration and Braking Assistance

Level 2 autonomy elevates the vehicle from a single driver assistance system to multiple advanced driver assistance systems (ADAS) that can take over steering, acceleration, and braking events in set scenarios. But even though Level 2 automation is initiated on two fronts or more, the driver must actively participate at all times, either by monitoring system performance or keeping her hands on the steering wheel in preparation to take full control at a moment’s notice. Level 2 is commonly known as partial driving automation, and many new vehicles offer it as standard or available equipment.

Level 3 Automation – Conditional Self-Driving with Driver

The leap from Level 2 to Level 3 autonomation is significant, which is why no Level 3 systems are legal to use on American roads…yet. 

Level 3 is known as conditional automation and closely mimics an A.I.-type interface, in which the various driver assistance systems are programmed to make decisions on their own based on the changing driving environment around the vehicle. However, even though Level 3 automation is a predominantly driverless scenario, it requires a human driver to be present and able to take control of the vehicle at any time, specifically in the case of an emergency due to system failure.

Level 4 Automation – Conditional Self Driving Without Driver

Referred to as high-driving automation, Level 4 autonomy does not require any human interaction in the operation of the vehicle because the vehicle is programmed to stop itself in the event of system failure. So, for all practical purposes, there would be no emergency override needed. 

Level 4 is designed to allow the vehicle to travel from points A to B in self-driving mode, but typically within specific geographic boundaries. This mapped set of parameters is called geofencing. Other conditions can also limit the operation of a Level 4 autonomous vehicle, such as severe weather conditions.

Even though Level 4 can be wholly driverless, the vehicle will still include normal driving equipment such as a steering wheel and brake pedal so that a human being can take control whenever they desire. From an application standpoint, Level 4 vehicles are expected to be used mostly for ride-share and public transportation purposes.

Level 5 Automation – Unconditional Self Driving

As the highest classification of autonomy, Level 5 translates to full driving automation. With zero human interaction required, Level 5 vehicles will not have steering wheels, pedals, mirrors, or even a windshield. They will be designed to transport human beings comfortably and efficiently without a driving experience. And they will not be bound by geofencing nor affected by weather. Level 5 vehicles will be completely driverless. The only human involvement will be to set a destination.

The information in this article is from the Society of Automotive Engineers (SAE). It was accurate on September 8, 2020 but may have changed since that date.