A lot of companies are working on self-driving cars but the day when we all hurry around in pods without steering wheels is a long way off.

In the meantime, self-driving technology will slowly filter across to cars in piecemeal form, with the Society of Automotive Engineers in 2014 presenting a roadmap of five key levels of capability that we'll pass on the road to fully self-driving cars. It can be confusing, so BMW released a video that explains the differences between the levels with the aid of visuals.

In terms of production cars, we've already passed the first two levels: Level 1 is basic cruise control with automated acceleration and braking, while Level 2 introduces some automated steering into the mix. Importantly, both these levels require full driver attention at all times as their functionality is still very limited.

The next milestone will be Level 3, which BMW expects to introduce on its iNext electric car arriving in 2021. Level 3 means the driver in a set range of situations can let go of the steering wheel and even look away for extended periods, though they have to be ready to take over within seconds which could prove dangerous. Because of this major onus on the driver, many firms are choosing to skip Level 3 and go straight to Level 4.

BMW self-driving technology

BMW self-driving technology

Level 4 capability is essentially the same as Level 3, with the key difference being the timespan required for the driver to take back control being far longer, think minutes versus seconds. Another important distinguisher of Level 4 capability is that the vehicle is able to bring itself safely to a stop should the driver fail to take back control. For this reason, BMW says a driver in a Level 4 self-driving car could safely fall asleep behind the wheel. BMW is developing Level 4 self-driving technology alongside Level 3 technology but doesn't expect regulations and necessary infrastructure (think detailed maps and communications infrastructure) to be ready until the middle of the next decade.

There are already some Level 4 cars on the road, though. Waymo's self-driving cars are currently at Level 4 capability but limited to where they can drive. Waymo plans to use the technology for the first commercial self-driving taxi service later this year in Phoenix, Arizona. An engineer will still be onboard for monitoring, though.

The final goal is Level 5 capability, where a car can operate without the need of a driver. BMW says this likely won't be ready until the end of the next decade.