What are SAE's five self-driving levels?

PC Magazine defines autonomous vehicles as a “computer-controlled car that drives itself.” In other words, human drivers are never required to take control but rather rely upon sensors and software to control, navigate, and drive the vehicle. ABI Research forecasts that by 2025 we’ll see approximately 8 million autonomous or semi-autonomous vehicles on the road. But before they can hit the road, self-driving cars will first have to progress through 6 levels of driver assistance technology advancements.

illustration from inside driver console finger pushing button
Some future vehicles will have no steering wheel at all. (Pxhere)

The word “autonomous” might not be the correct term for self-driving capabilities as it infers that the vehicle has capabilities beyond mechanical, or rather it’s “self-aware” and capable of making choices on its own. Think of it like asking your car to drive you to work, but it decides you’d be better off visiting the beach instead. The Society of Automotive Engineers (SAE) uses the term “automated” instead, meaning the vehicle must follow the orders of the driver/passenger, giving them some level of control, even if it’s simple orders. Regardless of the definition, self-driving vehicles are classed within several levels of autonomy that range from 0 (I’m just a regular car) to 5 (I don’t need you to drive). The breakdown  follows:

SAE Level 0: No automation

Vehicles at this level have no autonomous capabilities, meaning the driver is in complete control of the vehicle at all times, even if it is equipped with warning and intervention systems, including obstacle avoidance and emergency braking systems. There are no bells and whistles here, just your ordinary cruise control to help with long-distance driving and minimize the risk of a speeding ticket from a lead foot. Those enhanced driver safety systems are excluded from the automation categoric system as they do not perform part or all of the DDT (Dynamic Driving Task) on a sustained basis; instead they provide brief intervention during potentially hazardous situations.

SAE Level 1: Driver assistance

Level 1 is the most basic type of autonomy and safety, where one element of the driving process is taken over in isolation, using data from sensors and cameras, but the driver is very much still in charge. Here we can find adaptive cruise control and lane-keep assist technology to help with driving fatigue. Adaptive cruise control will maintain a safe distance between you and the vehicle ahead of you by utilizing radars and/or cameras to automatically apply braking when traffic slows and resume speed when traffic clears. Lane keep assist may also be present and will help nudge you back into the lane should the vehicle start to veer out of it. These technologies were introduced in the late 1990s at Mercedes-Benz, with its pioneering radar-managed cruise control, while Honda introduced lane-keep assist on the 2008 Legend. These were the first steps towards the development of an actual autonomous vehicle.

SAE Level 2: Partial automation

At this level, things get a bit more interesting. Although the driver must have hands on the wheel and be ready to take control at any given moment, level 2 automation can assist in performing rudimentary tasks. The driver still needs to perform tactical maneuvers such as responding to traffic signals, changing lanes and scanning for hazards. Vehicles at this level are typically equipped with advanced driving assistance systems (ADAS) that can take over steering, acceleration, and braking in specific scenarios. These systems are beneficial in stop-and-go traffic scenarios by maintaining the distance between you and the vehicle in front of you while also providing steering assistance by centering the car within the lane. Tesla Autopilot, Volvo Pilot Assist, and Audi Traffic Jam Assist are some examples of Level 2 autonomous capabilities.

SAE Level 3: Conditional automation

The progression from Level 2 to Level 3 is substantial from a technological standpoint but subtle, if not negligible, from a human perspective. The SAE calls Level 3 ‘conditional automation,’ which is a specific mode that handles all aspects of driving but the driver must be ready to respond to a request to intervene. Autonomous vehicles at this level are capable of driving themselves, but only under ideal conditions and with limitations, such as limited-access divided highways at certain speeds. A human driver is still required to take over should road conditions fall below ideal. Some vehicles at this level have “environmental detection” capabilities and can make informed decisions for themselves, such as accelerating past a slow-moving vehicle. Audi’s A8 is a great example and has the capabilities to drive itself under certain circumstances.

SAE Level 4: High automation

At Level 4, the vehicle’s autonomous driving system is fully capable of monitoring the driving environment and handling all driving functions for limited routes and conditions defined within its operational design domain (ODD). A steering wheel and pedals remain at this level but no human input or oversight is required except under certain conditions, such as road type or geographic area, poor weather and other unusual environments. The driver might manage all driving duties on surface streets then become a passenger as the car enters a highway. The vehicle may alert the driver that it is reaching its operational limits if those conditions dictate human intervention, such as heavy snow. If the driver does not respond, it will secure the vehicle automatically within specified safety parameters, including slowing down to a fuill stop.

SAE Level 5: Full automation

Vehicles at Level 5 are fully autonomous, meaning a driver is not required to perform all driving tasks. Autonomous vehicles at this level are not bound by geofencing nor affected by weather and can transport human beings comfortably and efficiently. Only the destination is the sole requirement to get from point A to point B. In fact, vehicles in this category may not come outfitted with steering wheels or gas/brake pedals. Passengers simply enter voice commands for onboard systems, such as entertainment, air-conditioning and video calling.

Although the technology for a fully autonomous car exists today, they are still in the development stage. Couple that with current regulations in the US and legal issues, and full-scale deployment of Level 5 vehicles are still many years away. That said, a report published by IHS Markit in 2016 forecasts that 21 million autonomous vehicles will be in use by 2035, slightly over a decade from today.