Ever since the likes of Herbie, KITT and the Batmobile graced our screens we've been enthralled by the idea of a car that can drive by itself. Volkswagen and Google have had a bash themselves with some success, but BMW has been quietly working on an autonomous car since 2005.

In fact, it's built two: a pair of 5 Series decked out with 12 exterior sensors that read the road around the car. They transmit information to a boot full of computer equipment, which processes it and talks to a highly advanced GPS system and next generation versions of BMW's active cruise control and lane marking detection systems.

When the first prototypes were ready, testing began on race circuits and the project became known as TrackTrainer. The engineers programmed the car to follow the best line on a circuit (as previously set by very good human racing drivers) and guarantee a perfect run every time.

The technology allows the car to travel with near pinpoint accuracy and it can now be used on the road. The driver does the work before and after joining a motorway and he or she has to remain in control all the time, so it's not a case of putting your feet up.

Once you've reached a steady motorway cruise, prod what would normally be the steering wheel's volume button a couple of times and the car takes over. The first indication that you're no longer in charge is the steering, which instantly begins to make tiny corrections of its own accord. The GPS system is so advanced that it allows the car to react to changes in the road surface, hence the small inputs from the wheel, so it's very comfortable and smooth.

The first few minutes are incredibly eerie. You loosen your grip on the wheel but, if anything, pay more attention to the mirrors and the road ahead. Eventually, your confidence grows, and you settle down to let the car do its thing.

It hugs the inside lane by default, but it's not afraid to overtake slow moving traffic. It will never gun for a gap, rather traverse lanes gently and only when there's plenty of space. The indicators give you plenty of notice about what it intends to do, but you still check the blind spot with your utmost meticulousness. The whole experience is exhilarating, fascinating and a bit frightening at the same time.

Inside, it's pretty much stock 5 Series, except for a monitor mounted on the centre console, displaying primitive, 1980s-style blue blocks. It's actually very sophisticated - the blocks represent other vehicles on the road and they vary in size depending on how big the obstacle is.

The technology isn't perfect, though. BMW wanted to drive from its headquarters in Munich down to Stuttgart, but road works on the route put pay to that, because the car can't recognise them yet. It's also not suitable for towns or minor roads.

BMW has no intention of producing the car, either. Instead, the autonomous 5 Series is a technological test bed for future driving aids that will appear on production models, and two soon-to-be-announced gadgets have been credited to it.

The first is congestion assist, which allows the car to drive automatically at up to 40km/h in heavy traffic. The second is emergency stop assist, which can detect a driver's sudden illness - like a heart attack or stroke - and independently pull the car to the side of the road and contact the emergency services.

There's no firm date on when we'll see either one, but BMW reckons that congestion assist is the closer of the two. With that in mind, it's probably worth looking out for on the next 7 Series.