Adaptive cruise: great until you have to go without it

Adaptive cruise is one of the plethora of supplementary safety systems to arrive in cars in recent years. First launched as Distronic in S Class Mercedes-Benzes around the turn of the millennium, it's now the norm in high-spec German models, and it's begun to trickle downmarket.

Such systems are now optional in many mid-level Germans and relatively low down the Lexus range -- it's standard in better equipped IS250 models. Toyota has even gone one better with the new Prius i-Tech, which offers it as standard.

Cruise control comes in several levels of sophistication. The base version, increasingly found standard on commuter models, allows the driver to impose a ceiling speed on the car. It's a fairly simple device, incapable of keeping the car to the set speed on downhill runs.

Better models come with what's often referred to as active cruise control, which harnesses wheel- and engine-braking to maintain the set speed downhill as well as uphill and on the flat.

Then there's adaptive cruise. Here, front-end radar sensors help it maintain not just the set speed but a set distance from the vehicle in front. When it senses that gap narrowing, it slows and overrides the speed setting to maintain that distance. All very reassuring. Maybe too much so.

Much has already been made of the hidden dangers of so-called electronic nanny systems like ABS and stability control, for the false sense of security they can induce in drivers. Back in 2002, New Scientist reported the 'risk compensation' factor of such systems -- surveys have shown how ABS mitigated its own virtues by encouraging drivers to take bigger risks. It showed how such systems are more pertinent to drivers pushing boundaries and stretching envelopes than to those commuting quietly between home, work, school and supermarket. The syndrome is also commonly known as the Peltzman Effect after work done at the University of Chicago by economist Sam Peltzman. His work was recently popularised in an episode of procedural forensics TV drama, CSI.

Adaptive cruise arguably presents a different -- and more immediate -- danger. A danger arising not in the vehicle thus equipped, but when you leave it and climb into one without it.

It takes only a day or two to get so used to such systems. Hit the freeway, flick it on and settle back to enjoy the ride. At least until someone changes lanes suddenly in front of you. In extreme cases brakes go on, beepers go off and belt pretensioners pull you back into your seat. After plenty of such warning, the system switches itself off and hands control back to you. All of which serves only to reassure you more.

Shifting out of said vehicle and into a lesser-equipped one, the normal way to discover the absence of adaptive cruise is via a series of jolting realisations that you're headed up the backside of the car in front. Which means drivers need to take special care in such situations.

There may come a time when automotive, radar and satellite technologies collude to render human operation of motor vehicles an option -- or maybe not even an option.

But that's a while away yet. And while we wait, auto makers keep serving up more and more technologies capable of keeping us from death and injury at our own hands. But as any old naysayer will tell you, every silver lining has a cloud. Adaptive cruise is just another case in point.

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