A self-driving car, also known as an autonomous car, driverless car, robotic car, or robo-car, is a car that is capable of operating with reduced or no human input. They are sometimes called robotaxis, though this term refers specifically to self-driving cars operated for a ridesharing company. , the term "self-driving" lacks an agreed standard definition and is also subject to commercial advertising and branding considerations.
In 2020, Waymo was the first to offer rides in driverless taxis in the operational design domain (ODD) of limited geographic areas, but , no system has achieved full autonomy in all domains - sometimes referred to as "Level 5" on a scale of 0 to 5 levels of automation defined by the global standards organization SAE International, or simply "no driver" as given by the classification system proposed by Mobileye in the US.
Following a history of experimentation and development of advanced driver assistance systems (ADAS) after World War II, two main technologies are now primarily used: LiDAR (Light Detection and Ranging), and visual sensors (cameras) which capture images and video like human eyes. These are combined with systems such as Global Positioning System (GPS), neural networks, artificial intelligence, and established ADAS engineering to deliver levels of driving autonomy.
The primary obstacle to self-driving is the advanced software and mapping required to make them work safely across the wide variety of conditions that drivers experience. However, the software is not yet advanced enough to handle all circumstances and has caused accidents and deaths. Other issues include security of over-the-air updates, legal and regulatory issues, ethics, and consumer confidence. Methods of testing and monitoring the reliability of cars have evolved in parallel with deployment, with various standards being proposed. Implications for urban infrastructure and the economy have also been discussed.
Public perception and acceptance of autonomous cars has been mixed. A survey in 2022 found only 27% of the world's population would feel safe in one. Public acceptance is also influenced by "self-AV bias", where drivers judge identical autonomous vehicle driving much more harshly than human.
History
Definitions Organizations such as the global standards body SAE International (SAE) have proposed terminology to describe technical capabilities. However, most terms have no standard definition and are employed variously by vendors and others. Proposals to adopt aviation automation terminology for cars has also not prevailed.
The first consideration is the operational design domain (ODD).
Vendors have taken a variety of approaches to the self-driving problem. Tesla's approach is to allow their "full self-driving" (FSD) system to be used in all ODDs as a Level 2 (hands/on, eyes/on) ADAS. Waymo picked specific ODDs (city streets in Phoenix and San Francisco) for their Level 5 robotaxi service. Up until January 2026, Mercedes Benz offered Level 3 service in highway traffic jams at speeds up to . (In January 2026, Mercedes removed the feature from its cars in favor of an upcoming Level 2 capability.) Mobileye's SuperVision system offers hands-off/eyes-on driving on all road types at speeds up to . GM's hands-free Super Cruise operates on specific roads in specific conditions, stopping or returning control to the driver when ODD changes. In 2024 the company announced plans to expand road coverage from 400,000 miles to . Ford's BlueCruise hands-off system operates on of US divided highways.
Names such as AutonoDrive, PilotAssist, "Full-Self Driving" or DrivePilot are used even though the products offer an assortment of features that may not match the names. Despite offering a system dubbed Full Self-Driving, Tesla stated that its system did not autonomously handle all driving tasks. Tesla vehicles remain at Level 2 automation and are therefore not "fully self-driving" and require active driver supervision. In the United Kingdom, a fully self-driving car is defined as a car so registered, rather than one that supports a specific feature set. The Association of British Insurers claimed that the usage of the word autonomous in marketing was dangerous because car ads make motorists think "autonomous" and "autopilot" imply that the driver can rely on the car to control itself, even though they do not.
Concepts The following are useful in understanding the various definitions and criteria in use for self-driving cars.
Driving systems Advanced driver-assistance systems (ADAS) automate specific driving features such as Forward Collision Warning (FCW), Automatic Emergency Braking (AEB), Lane Departure Warning (LDW), Lane Keeping Assistance (LKA) or Blind Spot Warning (BSW). An ADAS requires a human driver to handle tasks that the ADAS does not support.
ADAS contrasts to an automated driving system (ADS), which would be classified by SAE J3016 as Level 3 or higher.
Autonomy versus automation Autonomy implies that an automation system is under the control of the vehicle rather than a driver. Automation is function-specific, handling issues such as speed control, but leaves broader decision-making to the driver.
The European car safety performance assessment programme Euro NCAP defines "autonomous" as "the system acts independently of the driver to avoid or mitigate the accident".
In Europe, the words automated and autonomous can be used together. For instance, under Regulation (EU) 2019/2144:Regulation (EU) 2019/2144
"automated vehicle" means a vehicle that can move without continuous driver supervision, but that driver intervention is still expected or required in the operational design domains (ODD); "fully automated vehicle" means a vehicle that can move entirely without driver supervision;
Cooperative system A remote driver is a driver that operates a vehicle at a distance, using a video and data connection.
According to SAE J3016,
Self-driving The Union of Concerned Scientists defined self-driving as "cars or trucks in which human drivers are never required to take control to safely operate the vehicle. Also known as autonomous or 'driverless' cars, they combine sensors and software to control, navigate, and drive the vehicle."
The British Automated and Electric Vehicles Act 2018 defines a vehicle as "driving itself" if the vehicle is "not being controlled, and does not need to be monitored, by an individual".
Another British government definition stated, "Self-driving vehicles are vehicles that can safely and lawfully drive themselves".
British definitions In British English, the word "automated" has several meanings, such as in the sentence: "Thatcham also found that the automated lane keeping systems could only meet two out of the twelve principles required to guarantee safety, going on to say they cannot, therefore, be classed as 'automated driving', preferring 'assisted driving'". The first occurrence of the "automated" word refers to a UNECE automated system, while the second refers to the British legal definition of an automated vehicle. British law interprets the meaning of "automated vehicle" based on the interpretation section related to a vehicle "driving itself" and an insured vehicle.Automated and Electric Vehicles Act 2018
In November 2023 the British Government introduced the Automated Vehicles Bill. It proposed definitions for related terms:
Self-driving: "A vehicle 'satisfies the self-driving test' if it is designed or adapted with the intention that a feature of the vehicle will allow it to travel autonomously, and it is capable of doing so, by means of that feature, safely and legally." Autonomy: A vehicle travels "autonomously" if it is controlled by the vehicle, and neither the vehicle nor its surroundings are monitored by a person who can intervene. Control: control of vehicle motion. Safe: a vehicle that conforms to an acceptably safe standard. Legal: a vehicle that offers an acceptably low risk of committing a traffic infraction.
SAE classification
In 2014, the association for transport and other industries SAE International published a six-level classification system – ranging from fully manual to fully automated – as J3016, Taxonomy and Definitions for Terms Related to On-Road Motor Vehicle Automated Driving Systems; the details are revised occasionally.
The system was adopted by the United Nations Economic Commission for Europe (UNECE) in the form of UN Regulation No. 157, which came into force in January 2021, and used in over 50 countries. After SAE updated its classification in 2016, (J3016_201609), the US National Highway Traffic Safety Administration (NHTSA) adopted the SAE standard.
The classification is a topic of debate, having been criticized for its technological focus, with various revisions proposed. It has been argued that the structure of the levels suggests that automation increases linearly and that more automation is better, which may not be the case. SAE levels also do not account for changes that may be required to infrastructure and road user behavior.
Automation levels
The SAE classification of levels is based on the role of the driver, rather than the vehicle's capabilities, although these are related in the form of a "driving mode" (also known as a "driving scenario"). The mode is determined by both an operational design domain (ODD) and a "dynamic driving requirement". The ODD is the circumstance in which the car is driving, and the driving requirement is what the system must do while remaining safe within the boundaries of that ODD. These two things define the SAE level.
Cars may therefore switch levels according to the driving mode. A human analogy might be a mode in which you can stand unassisted on one leg (the requirement) if you are on the ground (the ODD), but would need support when standing on a tightrope.
Above Level 1, level differences are related to how responsibility for safe movement is divided/shared between the advanced driver-assistance system (ADAS) and driver, rather than specific driving features (see Concepts). A car might therefore have Level 3 capability for lane management (the driving requirement) up to 100 km/h (the ODD), but Level 2 at speeds faster than that. Or it might have Level 4 for driverless navigation on designated highways, but Level 2 on urban side roads.
ADASs that are considered Level 1 are adaptive cruise control, emergency brake assist, automatic emergency brake assist, lane-keeping, and lane centering. ADASs that are considered Level 2 are highway assist, autonomous obstacle avoidance, and automatic parking. At Level 3 and above, if a car is driving and the ODD changes—for instance, a clear highway becomes a construction zone with hand-signals from a worker—the system must recognize that it is exiting its ODD and fall back accordingly, including asking for driver intervention if necessary.
A fully self-driving car would therefore stay at Level 5 for all dynamic driving requirements in all circumstances (speeds, roads, terrains, visibilities, obstacle types, jurisdictions, etc.), while a car with no ADAS controlling the driving requirements would rely on the human driver for that, and stay at Level 0 regardless of the domain.