Self-Driving Levels and Tesla

Last updated 04-Sep-2023

SAE International have defined 6 levels of driving autonomy which is widely becoming the standard way to think of Self driving maturity. While there may be some practical differences in the way laws are written the SAE standards offer a good, high-level insight into the challenges each level brings. We look at them, discuss the cars and systems that fall into each bracket, and assess where Tesla sits, both now and in the near future.

SAE levels

SAE International have broken down the maturity of driver assist and self-driving capabilities into 6 levels, level 0 being effectively no more than passive safety systems, through to level 5 where the car can drive in all conditions and at all times to the same extent as a human driver.

The grading system doesn't focus specifically on feature count, it reflects more on how the share of driving accountability is split between the car and the driver, and importantly how the transition from one to the other occurs. This is an important distinction, and one which is material to law makers and regulators. It introduces a new component which is largely overlooked by Tesla, namely how the transition from the car to the driver and back needs to be managed over time, rather than an instantaneous hand back.

SAE levels


Accountability and Responsibility are words often used interchangeably in this context and can cause some confusion.

We're going to use:

  • Accountable: the entity that is in charge and legally on the hook if things go wrong. This could be either the driver or the car systems, but only one of them can be accountable at any given time.
  • Responsible: the entity that is actually undertaking the driving activity, this can be either the driver, the car systems, or a combination of both

To give an example, when using Traffic aware cruise control, the car is responsible for managing the speed and the distance to the car in front, the driver is responsible for steering. The driver alone is accountable for the driving. It's worth noting that the Tesla system has always had the accountability for the driving with the driver.

Levels 1 and 2

These levels do vary between themselves in feature count, but not in accountability. These are essentially driver assist aids. The driver is still always accountable, constantly monitoring the road and cars driving and be ready to immediately override any system should it deviate unacceptably from how the driver would like.

The difference between the two is down to the number of features. Level 1 is a single feature, typically adaptive cruise (speed) control, and has been available on cars for many years. Level 2 is the next logical step and is more than 1 feature, such as adaptive cruise control and lane keep. This has been available since 2015 when Tesla first enabled the Mobileye based Autopilot system which had both these features. It also had the ability to change lane and a simple forward and reverse summon feature. Parking assist systems have also been around for some time which can arguably also be classed as level 2 systems as they both steer and control the speed of the car into a parking bay, and some of these predate the Tesla autopilot system.

The key thing to appreciate is that the number of features on a level 2 system does not matters, this can be extensive and the car could even be responsible for all the driving duties including taking exits and crossing oncoming traffic, however the driver is still accountable. It is this accountability assignment that means the system is Level 2, and until the accountability starts moving the car, will always be Level 2.

Consequences for the driver

The driver must always be paying attention to the driving and be ready to step in instantly they detect a problem. If the car speeds, has an accident, or any other driving violation occurs, the driver is accountable for the mistake.

Level 3

This is the first level where the accountability for driving shifts to the car in certain, well defined, situations. This is the significant distinction between level 2 and level 3 and sometimes referred to as 'eyes off' driving. The driver still needs to be present, and needs to be able to take over both the accountability and potentially the responsibility for driving at short notice, but there are periods of time when the car will be accountable as well as responsible for the driving. The transition of accountability and responsibility between the car and driver needs to be carefully managed.

It may seem counter intuitive but it is entirely possible to have a car that can be responsible for all of the driving duties but is not accountable in any way, and therefore a level 2 system, and a car which is only responsible for the driving in a very tightly defined scenario where many of the wider driving activities do not occur such as taking junctions, but is also accountable in that scenario, and therefore a level 3 system. This is where many supporters of Tesla FSD fail to understand the real difference between the levels. i.e., the difference is not linked to feature account, but to the shift of accountability.

Legislation is starting to appear to approve Level 3 cars and two broad scenarios are emerging:

Both of these require the approved features to be highly reliable in themselves and not to abort unexpectedly. They are also able to understand when the limits of their accountability are being reached, to remain within them, and when to hand back accountability.

When the handover is time critical it poses the biggest challenge as it is essentially saying you cannot just revert accountability to the driver in an instant, which is the current Tesla way of working.

Traffic Jam assist

The first of the two scenarios above has been seen in systems sometimes called traffic jam assist. This has now been approved for Mercedes and other makes are likely to follow fairly quickly.

The environment where the system is accountable is tightly defined, it is only on motorways and currently at relatively low speed. As soon as the road changes or the speeds increase, the car requests the driver to become accountable. In this scenario the driver has little to assimilate; the road type is well understood and flowing freely and as the accountability transition occurs the car is highly likely to be able to continue as before.

An interesting aspect of this is the car typically continues to be responsible for the driving after the transition of accountability to the driver. In other words, using Tesla terminology, the car would remain on autopilot as the speed increases, the only change is the driver would need to acknowledge they are happy to resume accountability. Some have claimed the Mercedes system is inferior because of the speed restrictions, but this fails to recognise it is only the L3 aspect that is restricted, at L2 these restrictions do not apply.

General purpose level 3

The general-purpose requirements recognise that a driver who is not accountable, is not paying attention. They may have their eyes off the road and will need some time from the point of notification to the point of assuming accountability to regain cognitive and possibly physical control. If the driver needed to be alert and monitoring the situation then the car is not accountable and the situation is level 2.

The parameters for the transition are being discussed by the regulators and are expected to be between 7 and 10 seconds. To be clear, this is saying the car must remain accountable and responsible for driving safely for between 7 and 10 seconds after it has signalled to the driver that they will need to take over accountability. This is a very significant stipulation as the implications are:

The bar to achieve the general-purpose level 3 is difficult. Tesla are pushing forwards with the FSD programme in the USA and it is attempting to perform more and more tasks, including taking junctions and navigating across oncoming traffic. While these are all features the car could perform, i.e., be responsible for doing, we are doubtful that the accountability at level 3 will ever be granted for these system (Tesla may be looking to go straight to Level 4). We don't believe general purpose Level 3 will be possible beyond a fairly simple evolution of traffic jam assist type systems. Tesla are likely to miss out completely on Level 3 while their competitors will increasingly develop these systems.

Consequences for the driver

Under Level 3 the driver has some scope for other activities that can be quickly and easily stopped. This may be reading a text message, or watching television, but still needs to be relatively aware of the driving of the car and the context of where they are, in other words they are limited to eyes off the road.

If the car speeds, or has an accident when on Level 3 is a legal point that has not been resolved. Mercedes have said they will take accountability for accident damage, but the law has not yet developed to handle matters such as speeding. The current restrictions with the Mercedes system make this very unlikely, however it is a matter to be resolved in the fullness of time.

Level 4

Level 4 is a further advancement. Here the conditions that must be met for the car to be accountable are more predictable. This could be the type of road or the time of day, i.e., avoiding night time driving. It may also include certain weather conditions or traffic, but for the system to be activated, it must know where it will be driving and that it is capable of being accountable and responsible for driving that road for the foreseeable time. This is similar to level 3 driving, except instead of a 7 to 10 second notification, the car can predict exactly when its limits will be reached and the hand back of accountability can be performed over a much longer time window.

An example, and one we have previously written about, is driving on motorways/interstate highways/freeways for long periods of times. The environment is relatively well understood and predictable, the complexity of the driving is low with few complex junctions and often the traffic is all flowing in the same direction. The car could assess via the satnav how long they will remain on that road and only alert the driver to start preparing to take over as the end of that defined period is approached. This is similar to the traffic jam assist, except there are no artificial limits such as maximum speed, or traffic conditions that would prevent the operation.

Initially this sounds very similar to level 3, however the driver can be further removed from the driving situation.

Tesla may well be aiming for this level but the bar is pretty high. At present Tesla seem to be trying to have the full breadth of driving capability, but currently only the responsibility of the driving, and consequently Level 2.

It's important here to understand that it is not the ability to attempt to drive that matters, the Tesla system could be capable and responsible for driving coast to coast and handle 99.99% of journeys without incident, it is the management of the accountability that matters. In addition, the car cannot disengage or fail in any of the driving tasks it tries to perform.

Consequences for the driver

Under Level 4 the driver has a fairly wide scope for other activities. This may include working on emails (not just reading them), or reviewing documents, and the driver does not need to be aware of the driving context, safe in the knowledge the car is accountable and will be for some time. In other words, their mind can be switched off from the driving for a period of time.

Like Level 3, there are legal matters to be resolved regarding accountability for accident damage and driving mistakes such as entering a limited occupancy lane or speeding. There may be requirements to easily provide evidence on who was accountable at the time, and possibly the car needs to indicated the accountability state so other motorists and the police understand a driver who looks asleep is actually not accountable at that time.

Level 5

Level 5 is the easiest of all to understand, the car can simply drive itself without a human being present. This is the utopian goal that would enable robotaxi, but it is also the hardest to obtain without transitioning through the other levels.

Without a driver there are scenarios however where driving reaches a stalemate. Two Tesla's approaching each other on a single-track road, both being followed by other cars. When they meet, they both stop and neither are able to resolve the situation. That is not a scenario that can be allowed to happen.

Consequences for the driver

Under Level 5 you simply don't need a driver.

Other accountability considerations

As mentioned above, there are implications when the car is accountable. Insurance, dealing with the police should the car be involved in an accident, even if innocently, liability for speeding tickets or other driving offences such as entering a zone where the car is not allowed.

Even in use it may be a requirement for the car to indicate where the accountability lies. In many countries, using a mobile phone while driving is illegal, one would expect this to be relaxed when the car is accountable, but how is that enforced? If a Police officer currently sees the person behind the wheel to be holding the phone the conviction is clear, but how is this done when there are changes in accountability?

These details, and many more, need to be worked through, either with practical alterations to the car such as a visible status light, or laws changed and reworked. While this is not a Tesla issue as such, it is one for self-driving as a topic and can take many years to work through.

Our belief is the following logical stages will occur to achieve self-driving:

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