Levels of Autonomous Driving

#d Low-Level Autonomous Driving

Since its publication, the SAE International (formerly known as the Society of Automotive Engineers) Levels of Driving Automation have been the most frequently cited source in the industry. This video discusses the levels based on the latest revision of the “J3016 Standard” in 2021. External link to J3016,

Level 0 Autonomous Driving, also known as “No Automation.” At this level, vehicles are completely driven by humans without any autonomous driving features. The driver must control all functions of the vehicle.

Level 1 Autonomous Driving, known as “Driver Assistance.” In this level, the automation system can assist the driver with certain operations, but only one at a time (either longitudinal or lateral control). For example, when assisting with steering, it cannot assist with acceleration, and vice versa. This is also referred to as “feet-free”¹.

Level 2 Autonomous Driving, or “Partial Automation.” Here, the automation system can simultaneously control the vehicle’s acceleration, braking, and steering (both longitudinal and lateral). Notable products include Tesla’s Autopilot and Cadillac’s Super Cruise. However, drivers must remain alert and ready to take control at all times. Also known as “hands-free.”

In the 2021 version of the SAE standards, Level 1 and Level 2 automation systems are named “Driver Support Systems,” while Levels 3 to 5 are called “Automated Driving Systems.” In low-level autonomous driving, the driver is responsible for the entire operation of the vehicle. External link to J3016

#d High-Level Autonomous Driving

The jump from Level 2 to Level 3 is substantial, with Level 3 marking the beginning of true decision-making capabilities for cars.

Level 3 Autonomous Driving, also known as “Conditional Automation.” At this level, the automation system can control the vehicle’s acceleration, braking, and steering and make autonomous decisions in certain situations. When the autonomous driving system is engaged, the driver is allowed to perform non-driving related tasks without monitoring the driving, but must be ready to take over within a limited time when the system issues a “Takeover Request.”

Level 4 Autonomous Driving, also known as “High Automation.” At this level, the automation system can control all operations of the vehicle and does not require human interaction in most scenarios, offering a broader usage range than Level 3. The driver only needs to take control when a takeover request is issued. If the driver fails to take over within the limited time or the takeover is unsuccessful, the vehicle will perform “minimal risk maneuvers” to minimize harm to the driver.

Level 5 Autonomous Driving is the highest level of complete automation. The vehicle operates entirely autonomously without any need for human control interaction. At this stage, humans are purely passengers. However, the current description of Level 5 autonomous driving remains an ideal expectation and its commercial realization is still unpredictable.

Merat, N., Jamson, A. H., Lai, F. C. H., & Carsten, O. (2012). Highly Automated Driving, Secondary Task Performance, and Driver State. Human Factors, 54(5), 762-771. https://doi.org/10.1177/0018720812442087

Zeeb, K., Buchner, A., & Schrauf, M. (2015). What determines the take-over time? An integrated model approach of driver take-over after automated driving. Accident Analysis and Prevention, 78, 212-221. https://doi.org/https://doi.org/10.1016/j.aap.2015.02.023

Petermeijer, S., Bazilinskyy, P., Bengler, K., & de Winter, J. (2017). Take-over again: Investigating multimodal and directional TORs to get the driver back into the loop. Applied Ergonomics, 62, 204-215. https://doi.org/10.1016/j.apergo.2017.02.023

Huang, G., & Pitts, B. J. (2022a). The effects of age and physical exercise on multimodal signal responses: Implications for semi-autonomous vehicle takeover requests. Applied Ergonomics, 98, Article 103595. https://doi.org/10.1016/j.apergo.2021.103595

#d Main Differences

The main difference between Level 4 and Level 3 autonomous driving lies in the control capabilities of the autonomous driving system, usage scenarios, and the distribution of responsibilities.

Level 3 autonomous driving systems can only operate in specific environments, such as highways and certain urban roads. In Level 3 mode, drivers are allowed to perform non-driving tasks but must quickly take over vehicle control following a “Takeover Request” to handle emergency situations. The responsibility for driving post-takeover rests with the driver, while the responsibility before takeover lies with the autonomous vehicle (company).

In contrast, Level 4 autonomous driving systems can operate in a wider range of scenarios, including different urban road environments. Level 4 systems can achieve fully autonomous driving without the need for human drivers to remain alert and ready to take over vehicle control. Although there are still situations where human intervention is required in Level 4, the driving responsibility is entirely borne by the autonomous vehicle (company).

#c Information Limitations

It’s important to note that even Level 4 autonomous driving systems may not be able to handle certain special circumstances, hence a certain level of response capability and responsibility awareness is still needed.

Moreover, the aforementioned definitions of Levels 3 and 4 (especially Level 4) require the joint advancement of corresponding laws, regulations, and road infrastructure. It’s not something that can be achieved by just one vehicle alone.

---