Active Cruise Control: A Smart, Safe Choice

By Samuel Greengard

Posted April 22, 2008, at 1 p.m.

It's easy to forget how tedious it is to drive long distances — and how much concentration it takes. Spend a few hours on the highway, and you're likely to find your speed drifting upward and downward. You may also discover that as you grow tired and your reactions slow, it's difficult to maintain a safe following distance.

Although traditional cruise control systems help alleviate some of the drudgery of managing the pedals, these systems aren't smart enough to make driving effortless. As a result, many motorists skip cruise control systems altogether, finding them inconvenient and even downright distracting.

Enter Active Cruise Control (ACC), also known as adaptive or intelligent cruise control. These systems use either radar or a light beam, along with software, to maintain a preset speed in relation to traffic and changing conditions. ACC allows the vehicle to change speeds as needed — without driver intervention.

Moreover, ACC systems can help improve traffic flow by managing braking and acceleration more efficiently than people can. Ardalan Vahidi, assistant professor of mechanical engineering at Clemson University in Clemson, S.C., says that ACC helps "improve the capacity of highways" and brings motorists and traffic engineers closer to achieving automated driving. Eventually, engineers hope to create "queues of vehicles that [travel close together] at highway speeds without the risk of crashes," he says.

Into the Fast Lane

Though ACC brings the futuristic concept of automated driving one step closer to reality, it's already a tangible solution to the rigors of driving on today's crowded highways and roadways. These systems are now integrated into a growing array of vehicles, including models from Acura, Audi, BMW, Cadillac, Lexis, Mercedes and Volvo.

Here's how it works: ACC sends out a signal that detects slower-moving vehicles up to 500 feet in front of it. An onboard computer calculates the distance and relative speed. At that point, the system slows the car until the other vehicle moves away, and some systems can even bring a vehicle to a complete stop. Then, when it's safe, the car automatically speeds up again.

Some vehicles also feature a collision warning system that provides an alarm to warn a motorist that it's essential to brake in order to avoid a collision. As with conventional cruise control, you switch the system off by tapping your foot on the brake.

Two types of ACC systems exist: light-based and radar-based devices. Light-based systems, commonly referred as lidar, are less expensive than radar-based devices. However, they're less effective in inclement weather and are not able to track dirty vehicles or animals well because they lack reflectivity. These systems are typically mounted on the outside grille area of the vehicle (using a sizable black box). They cost approximately $400 to $600.

Radar systems, which are now available on most luxury vehicles, are often hidden in the grill and are offered as an option for $1,000 to $3,000. They can detect another vehicle drifting into your lane or an obstacle, such as a large animal, in your path. The vehicle automatically takes action and applies the brakes faster than a person can apply them. It does this by readying the braking system so that brake pads are closer to the wheel rotor and building pressure on the brake faster than a person can apply it.

ACC offers other features. For example, newer systems, such as those on the Acura RL and the Lexis 430/460, offer integrated Collision Braking Systems that alert a driver to an object up to 100 meters ahead by braking slightly and tugging on the seatbelts as an alert. If the driver doesn't react, it brakes hard and locks the seatbelts.

Industry analysts believe that 10 percent of vehicles will use ACC systems by 2010.

Going the Distance

Despite enormous advances, ACC technology isn't perfect. For one thing, not all systems work well in crowded urban environments. Some do not let a motorist get closer than a set distance, typically 100 to 200 feet. Consequently, other drivers are likely to pull around a vehicle and change lanes in front of it. At that point, the system is likely to slow the car even further.

Another issue is that these systems add buttons and controls that can prove confusing to motorists. Finally, ACC is still a relatively expensive option that many consumers cannot afford.

Nevertheless, the technology is making driving safer — and less stressful. And, in the future, ACC will become more sophisticated.

Engineers are currently perfecting on-board cameras that can differentiate between moving and stationary objects. They're also adding cameras and other systems that can detect when a driver is drowsy or inattentive and apply the brakes with a series of quick, short jabs — or offer an audible warning. If the driver doesn't react, the system will typically decelerate the vehicle and prepare for a crash by closing the windows and sunroof, tightening restraint belts, prepping air bags and adjusting seats to minimize the risk to passengers.

Make no mistake, ACC promises to give drivers a break … by braking and accelerating more efficiently. "With ACC, driving in traffic becomes remarkably less tiresome," Vahidi says.

Bio: Samuel Greengard is a veteran technology journalist based in West Linn, Ore. His articles have appeared in numerous publications, including Discover, Wired, American Way, Hemispheres, Acura Style, Ford Times, and the AAA publications Journey and Westways.

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