We're doing 130kph on the inside lane of a wide motorway near Munich, Germany, and I can see the rear of a large lorry looming in the middle distance. Normally, I'd check the mirrors, signal and move out to overtake in plenty of time before slipping back in front of the slower traffic. Today, however, both my hands are behind my head and my feet are lying flat on the floor in front of me. Is disaster imminent? No, the car calmly does the indicating, blind spot checking and lane changing for me so I can relax. This could be the future if BMW has its way; this is a driverless car and we're on a public road.
Driverless cars have been the stuff of science fiction for years. Herbie, KITT, the Batmobile - they've all captivated audiences with their ability to hit the road by themselves. Ironically, it was the Bond film Tomorrow Never Dies that spawned a not totally driverless but at least remote-controlled BMW 750i, and now the same car manufacturer has developed a pair of driverless 5 Series saloons.
The German firm isn't the only manufacturer to take on a self-driving car. Volkswagen has a Passat estate with a "temporary autopilot" function, and perhaps better known is Google's driverless car project, which was doing rather well until it crashed in California - supposedly due to human error, rather than a mechanical hiccup.
BMW arguably has the most complete and usable version of the technology yet. Save for the big ConnectedDrive decals along the sides, you wouldn't know the difference between this car and a standard 5 Series. Look closer, though, and the minute differences become apparent.
The exterior is adorned with small sensors, cameras and a few more aerials than usual. There are a couple of square sections missing in the front bumper, and one at the rear housing a similarly innocuous black rectangle.
In total, there are 12 sensors, each of which sends messages to a colossal amount of computer equipment in the boot - so golf club space is out of the question. They, in turn, talk to a highly advanced GPS system and next-generation versions of BMW's active cruise control and lane marking detection systems. All that technology allows it to travel with pinpoint accuracy and avoid other traffic, though the driver can override the system at any time by braking, accelerating or steering, similar to conventional cruise control.
"We began looking into this six years ago," says BMW's project director, Professor Raymond Freymann. "We made the first cars drive around race tracks, but travelling around a circuit at 50kph is not very sexy." At this stage the project was known as TrackTrainer and engineers programmed the car to follow the best line on a circuit (as previously set by human racing drivers) to guarantee a perfect run every time. This progressed to high-speed runs, much to Prof Freymann's delight: "Three months ago we went around the Laguna Seca with the technology in a 335i. We were driving [automatically] on the limits all the time and no one could keep up with us."
Consistently brilliant laps do not make for entertaining racing, though, so the project was taken to the open road. BMW chose the 5 Series for the road variant because, when the project started, it had more existing sensors for the likes of assisted parking and active cruise control so it required less retro-fitting of electric gadgetry than any other model in the range.
Save for the lack of a boot, it's a pretty conventional 5 Series interior. The one obvious change inside is the addition of a large monitor on the dash. It sits on the passenger side corner of the centre console, angled slightly towards the driver, and displays what looks like an archaic computer game from the 1980s. But looks can be deceiving - along with images from the front and rear cameras, a series of blue blocks of varying sizes regularly pop up and move longitudinally down the screen. These represent the vehicles around the car on the road - longer ones for lorries, shorter ones for cars, giving you an idea of just how clever the technology is.
At the moment this prototype is only capable of travelling independently on motorways, so we tested it on a stretch of autobahn outside Munich. Until you reach a main road, it's every bit as conventional to drive as a normal car. Bring it up to a steady cruise and settle into a motorway lane and you're ready to let the car do the work. Pushing what would normally be the volume button on the steering wheel a couple of times operates the automatic drive system, and it's a very gentle takeover. You loosen your grip on the wheel, though not completely at first, and become aware that the steering is making regular, minute corrections by itself.
The first few minutes are eerie. If anything, you're inclined to pay more attention to the road ahead and check the mirrors a little more regularly than usual, especially during a lane change. In the interests of good road manners, the car defaults to the inside lane, but it's happy enough to overtake slow-moving traffic. It won't gun for a gap like you would on a busy road though; instead it gently traverses the white lines when there's space, giving you plenty of warning with the indicators.
Eventually, your trust in the technology grows and you settle down to let the car do its thing. Rarely have the sensations of relaxation, fascination and fear ever gone hand-in-hand quite so well. It's very mindful of other traffic, erring on the side of caution and space, but it's also smooth and unhurried. The technology is so accurate that the GPS system knows almost to the centimetre where the car is on the road. That allows it to react to changes in surfaces and other documented road furniture, so, if anything, it's more comfortable a ride than you'd get from most human drivers.
This is still a prototype, so BMW's engineers were quick to reinforce the fact it's not a case of feet up and relax. The driver has to be able to intervene at any time, so keeping a loose hold of the wheel is advisable. If, for some reason, anything stops working, the speakers emit a loud, high-pitched buzz to prompt the driver to take control. The same noise can be heard if you make the slightest input of your own accord, as the system automatically returns control to the driver. That's what happens when you want to turn off the motorway - nudge the wheel, listen out for the buzz and it's over to you again.
Impressive though it is, the technology isn't perfect. BMW wanted to cover a lengthy motorway journey from its Munich headquarters to Stuttgart, but wasn't able to because of road works, which the car is, as yet, unable to recognise or deal with. It isn't suitable for town or country roads yet, either.
So when will we be able to put our feet up and let the car do all the work? "There is no intention whatsoever to put an autonomous car into production," says Prof Freymann. "This project is to help develop driving aids and localise sensors on the exterior of the car."
In short, it's actually a technological guinea pig for gadgets that will appear on future production models.
Two forthcoming systems that have benefited from the use of the automated car are emergency stop assistance and congestion assist. The former can monitor the driver's health and pull onto the side of the road in the event of, say, a heart attack or a stroke. It sounds a warning first and, if the driver fails to react, it automatically pulls over and contacts the emergency services. Congestion assist allows the car to drive independently up to 40kph in heavy traffic, so it's effectively a high-tech version of the company's existing active cruise control.
BMW wouldn't say when either one would become available on a production car but it hinted that congestion assist is the closer of the two. With that in mind, it's probably worth keeping an eye out for the next 7 Series. Until then, keep your hands on the wheel.