Self Driving Cars
The five levels of driverless car autonomy explained
General Motors

The five levels of driverless car autonomy explained

From cruise control to sleeping behind the wheel, these are the stages of driverless technology

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It was long predicted that 2020 would be the year of the driverless car. Instead of merely offering driver assistance systems like Tesla's Autopilot, car manufacturers and technology companies alike believed 2020 would see the commercial debut of self-driving taxis, whisking us from A to B with no human input.

But, as we recently wrote about, this reality is yet to be realized. Elon Musk's bold claims that Tesla cars would act as driverless taxis, earning money while their owners were in the office or on the beach. Instead, the industry is still yet to truly break into the second half of the five levels of autonomous driving.

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Set out by the Society of Automotive Engineers and referred to by almost all car manufacturers and driverless tech firms, each of the five levels defines a set of autonomous capabilities. It was hoped that vehicles capable of level five autonomy would exist in 2020, but so far this is not the case. Instead, the industry is generally hovering somewhere between level two and level three.

This is a slightly awkward place to be. According to the SAE, levels zero through two are "driver support features," while levels three through five are "automated driving features".

The technology can be confusing. Understanding what each autonomous car is capable of — and exactly when the car, not the driver, is responsible its own actions, is still unclear to many.

To help add some clarity, here is how the grading system works:

First, the SAE explains the key differences between levels zero to two, and levels three to five. Regarding the former, the SAE states: "You are driving whenever these driver support features are engaged – even if your feet are off the pedals and you are not steering...You must constantly supervize these support features; you must steer, brake or accelerate as needed to maintain safety."

As for levels three, four and five, the SAE describes these are: "You are not driving when these automated driving features are engaged – even if you are seated in the driver's seat." Then for level three, the SAE stats that, when the car requests, the driver must retake control of the vehicle. As for levels four and five, cars with these capabilities "will not require you to take over driving".

With all that taken care of, here is a quick look at each level individually.

Level Zero: No automation

This includes vehicles with regular cruise control where the car maintains a steady speed set by the driver. Because the car does not slow down to maintain a safe distance from the vehicle in front, the driver remains fully in control — they're just using buttons on the wheel instead of the pedals. Systems which provide warnings are also included in level zero.

Interestingly, automatic emergency braking is considered by the SAE to be a level zero feature, despite it actively taking control and stopping the car if it senses a low-speed collision is about to happen.

Level One: Driver assistance required

Where regular cruise control is Level Zero, radar-guided cruise control gets promoted to Level One. Many new cars have such a system, which adjusts the car's speed based on the vehicle ahead. You just set the maximum speed, then when the car ahead slows down and speeds up (up to your pre-set limit) yours will do the same and maintain a safe gap.

Lane keeping assistance, where the car gently nudges the steering wheel in your grip to stay in-between the road lane markers, is also an example of Level One autonomy. Despite these systems giving some elements of control to the car, the driver is legally in ultimate control of the vehicle at all times. An accident would be the fault of the driver using the systems incorrectly, not the systems themselves.

Importantly, the SAE notes that a level one vehicle may have lane-centering or adaptive cruise control, but not offer both at the same time.

Tesla Model 3All cars sold by Tesla are available with the company's Autopilot driver assistance system Tesla

Level Two: Partial automation

This is where most autonomous systems are today, in mid-2020, however there are some exceptions.

These level two systems work by combining radar cruise control with a lane-keeping assistant to keep your car in its lane and at the correct speed while on the highway.

Level Two systems can look mightily impressive, but in reality the car is doing little more than following the leader or keeping between the white lines. These systems cannot deal with city center road networks, junctions, pedestrian crossings, single-lane roads with no markings, poor weather and many other situations. As before, the driver is fully accountable for the actions of the car and can place no blame on the system in the event of a collision.

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Level Three: Conditional automation

This is the most confusing part of vehicle autonomy, because it covers the gray area of computers handing back control to the driver at a moment's notice. Audi was among the first to offer Level Three autonomy with the Audi AI Traffic Jam Pilot system on its A8 luxury sedan. However, the feature (which was due to arrive via a software update) never materialized, and removing your attention from the road while using any form of driver assistance system still isn't legal.

It could be argued that Tesla's latest version of Autopilot is a level three system, as it technically allows the vehicle to drive itself under certain conditions, such as when on a multi-lane freeway with a central divider. When enabled, Autopilot manages the accelerator, brakes and steering to stay in lane, but also shift lanes to overtake or merge onto new roads.

The SAE states that "traffic jam chauffeur" is a form of level three system. This is offered by Tesla, BMW and others, where the car moves itself in stop-start traffic, following the vehicle in front. The SAE says of level three (and four): "These features can drive the vehicle under limited conditions and will not operate unless all required conditions are met."

Level three is a gray area as the driver is expected to take back control when requestediStock

Because it is such a gray area, auto makers are keen to skip Level Three and jump straight from Level Two to Level Four, but this technological leap is yet to happen.

Level Four: High automation

This is what automakers are currently working towards and describes a system where the car is capable of driving itself almost all of the time. This includes highway driving (at any legal speed), as well as town and city driving where the road layouts are far more complex.

Level Four cars like this Lagonda concept make driving optionalGearBrain

Single-lane country roads are also theoretically included in a Level Four vehicle's skill set, although poor weather and unusual events (complex roadworks and diversions, for example) will require the driver to take back control. Or, in the case of an autonomous taxi like those offered by Waymo in Arizona, the vehicle may need to be controlled remotely by an operator, should it encounter a situation it doesn't understand.

Level Four autonomy featured on several concept cars at the Geneva motor shows in 2018 and 2019. Aston Martin's revived (and since mothballed) Lagonda brand showed off a luxury electric limo concept in 2018, also boasting Level Four driving — again, this is merely a claim for now and unlikely to be reality until the next decade, at the very least.

The SAE says level four vehicles use systems that "will not require you to take over driving," and lists examples as a "local driverless taxi," and vehicles where the pedals and/or steering wheel "may or may not be installed."

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Level Five: Full automation

Completely theoretical for now, Level Five autonomy is where humans have no control over the vehicle at all — other than telling it where to take them. Such cars are hoped to one day navigate all kinds of roads without issue, no matter what the weather conditions are like, and allow passengers to work, eat, read or even sleep while onboard. This is the end goal for Waymo and many others, but is still some way off. Waymo is operating some vehicles with no one sat behind the wheel, but these can be controlled remotely and are followed by another vehicle (driven by a human ready to take over) at all times.

Musk said in the spring of 2017 that one of his cars would drive from a parking lot in California to a parking lot in New York without its driver touching any controls for the entire journey. After promising to conduct this test in late-2017, it is yet to actually happen, as of July 2020. Musk, well-known for delivering late, also said Tesla owners would be able to sleep in their cars by 2019, a claim which also failed to become reality.

What will prove tricky for car manufacturers is the SAE's claim that a level five system should be able to "drive the vehicle under all conditions".

Building a truly autonomous car is difficult – Daimler admitted as much in late-2019 – and while a Tesla seemingly driving itself feels like we are living in the future, for now at least Autopilot and others like it will continue to act as driver assistance rather than driver replacement.

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