Self Driving Cars
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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Much was said at the Geneva Motor Show about self-driving cars and autonomy. From production-ready lane guidance systems, to electric hypercars lapping tracks as quickly as professionals, and commuter vehicles with no steering wheel at all, there was more technology at this year's show than ever before.

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. Thankfully, much of the auto industry follows a guide to autonomy established by the Society of Automotive Engineers (SAE).

This guide grades vehicle autonomy from Level Zero to Level Five, giving manufacturers a quick way to explain what their cars are capable of, and consumers a way to compare one driverless technology with another. Here's how the grading system works:

Level Zero: No automation

This covers a wide range of older vehicles, such as those which have no driver aids whatsoever; no ABS, no traction control and so forth. It also 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.

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 assistant, 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.

Today's Teslas use a version of Level Two autonomyGearBrain

Level Two: Partial automation

This is where the majority of autonomous systems are today, in early 2018. Tesla Autopilot, Mercedes Drive Pilot, Volvo Pilot Assist — these are all examples of Level Two autonomy, despite what the manufacturers might try and have you believe.

These 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. The systems will also take control in stop-start highway traffic, following the vehicle in front, stopping and starting when required. Some Level Two systems like Tesla Autopilot have additional tricks, like the ability to switch lanes when you use the indicator.

Level Two systems can look mightily impressive, but in reality the car is doing little more than following the leader or keeping between the while 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.

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 is the first manufacturer to offer Level Three autonomy with the Audi AI Traffic Jam Pilot system on its A8 luxury sedan.

When enabled, Audi's system actively takes over control of the car and the monitoring of its surroundings. Where Level Two technology requires constant attention from the driver, Level Three does not — but only to an extent. For example, Audi's system can drive the A8 in highway traffic at up to 37mph, but beyond that speed the driver must take back control.

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

The driver must also take control whenever the system issues a request to intervene, such as when it encounters a situation it cannot handle Because this could happen unexpectedly — and in a split-second — the driver must realistically remain alert for the whole journey, just as they do with Level Two. Despite this, when launching the new A8 Audi claimed that — once road laws have changed — drivers will be able to watch TV while the car drives them.

Because it is such a gray area, auto makers are keen to skip Level Three and jump straight from Level Two to Level Four.

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.

Level Four autonomy featured on several concept cars at the Geneva motor show. The Rimac C_Two electric hypercar is claimed to have Level Four — or rather, it is claimed to once it actually goes into production. Meanwhile, Aston Martin's revived Lagonda brand showed off a luxury electric limo concept also boasting Level Four driving — again, this is merely a claim for now and unlikely to be reality until the next decade.

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 will 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 Google and Uber, who want to offer robotic taxi services for customers who aren't able to get around on their own.

Such systems require more hardware than less autonomous vehicles — multiple cameras, plus radar and LIDAR systems. However, Tesla boss Elon Musk has claimed for some time that all Teslas built over the last two years have all of the hardware they need to fully drive themselves. It is just a case of the software (and the laws) catching up, he says.

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. Musk, well-known for delivering late, also said Tesla owners would be able to sleep in their cars by 2019, a claim which now seems unlikely.

A more likely short-term scenario is that Level Five vehicles will be used in controlled environments, such as for shuttle passengers around airports, or in large, open pedestrianised areas.

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