Adaptive Cruise Control: Meet Your New Co-Pilot

auto0303cruise_A1_195.gif Radar-based adaptive cruise control systems, on the Mercedes-Benz E500 and Jaguar XK-R, measure the time it takes for the waves to return to an emitter.

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Adaptive cruise control may be the future, but it's not that future. You know the one: The fantasy future of highways that control traffic electronically while drivers kick back like limo passengers. Try that with one of these cars and you'll wrap yourself around a tree.



Instead, think of adaptive cruise as a full-time digital co-pilot, actively monitoring the traffic ahead and adjusting the throttle-or even applying the brakes-to help you maintain a safe distance from the car in front of you. Should your closing speed exceed the system's braking limits (most supply up to 20 percent of maximum braking), an alarm warns you to take evasive action.



Obviously, any system designed to assume some of the driver's responsibility for safe driving is fraught with technical challenges and liability pitfalls. We decided to assess the first four adaptive cruise systems in production, found on the Mercedes-Benz E500, Jaguar XK-R, Infiniti Q45 and Lexus LS430.



There were two types of sensors in our fleet: The Europeans use radar; the Japanese, laser. Radar-based systems bounce microwaves off the target vehicle; lasers read the reflection of the car ahead. Radar has a slight advantage on paper because it's unaffected by dense fog, heavy snow or rain, or thick smoke and the like, but then drivers should not be using cruise control in those conditions anyway.



The trickiest bit of engineering: accurate target acquisition. If the scanned field is too broad, the system will pick up vehicles in other lanes; if the sensor scans too far forward, it will pick up oncoming traffic around curves, causing needless deceleration.



To determine how well the technology works, we conducted three real-world tests. The results are encouraging, especially from the radar-based systems.