Adaptive Cruise Control (ACC) Technology

Adaptive Cruise Control

Traditional cruise control—first offered in the United States on 1958 Chrysler models—certainly comes in handy on long drives. But cruise control has one drawback: it relies on the driver to judge the “closing” distance between their vehicle and the one in front. As automotive technology continues to evolve, traditional cruise control is gradually being replaced by adaptive cruise control (ACC).

What is adaptive cruise control?

Adaptive cruise control—a more technologically advanced version of the traditional cruise control system—allows drivers to maintain a pre-set speed while the system automatically monitors the traffic patterns and adjusts the “closing” distance by using the throttle and the brakes to maintain a pre-set distance behind the vehicle ahead. Unlike traditional cruise control systems that are only linked to the throttle for limited acceleration capabilities, adaptive cruise control “reads” traffic conditions and modulates the throttle and the brakes to keep the vehicle a safe distance from the vehicle in front of it. The earliest versions of adaptive cruise control were designed exclusively for driving at higher speeds and did not work at speeds below 20 miles per hour or in stop-and-go situations.

How does ACC work?

When the driver activates the ACC system, a microwave radar unit, a light-based unit (called lidar, which is located on the front of the vehicle), or cameras mounted on the front of the vehicle begin to scan for other vehicles or objects within a distance of nearly 500 feet in front of the vehicle. When the system senses a vehicle or object, it calculates the distance and relative speed and the onboard computer then automatically sends a message to apply the brakes to maintain a pre-programmed distance behind it. When the traffic has cleared or the object has moved, the system will accelerate the vehicle back to the previously set speed. Like traditional cruise control, an adaptive cruise control system is cancelled when the driver applies the brakes.

Unlike human operators, whose vision can be compromised in fog or rain, adaptive cruise control is not affected by weather conditions, which adds value as an active safety feature designed to help drivers avoid accidents during inclement weather.

ACC can help reduce rear-end collisions and traffic congestion

Rear-end collisions are the logical starting point for accident prevention, as they are the most common type of crash. Of the nearly 6.2 million police-reported collisions in 2005, 29.6 percent were rear-end collisions, according to the National Highway Traffic Safety Administration (NHTSA, www.nhtsa.gov). An ACC system can help reduce the likelihood of a collision with the vehicle in front, since the system can apply the brakes more quickly than a driver can react. But even if the adaptive cruise control system applies the brakes, the driver must take over, as most current systems will only slow the vehicle down, not bring it to a stop. However, there are several ACC systems on the market that will bring a vehicle to a complete stop in traffic, and then accelerate back to cruising speed as traffic lanes open.

Some drivers have a tendency to slam on their brakes and use heavy throttle in traffic. Many new vehicles have an advanced version of ACC that operates in stop-and-go traffic and can help alleviate this problem, as ACC systems have been proven to modulate brakes and throttle much smoother than most drivers could, thus nearly eliminating this congestion-forming phenomenon.

Who needs adaptive cruise control?

In simplest terms, ACC is a highly evolved version of cruise control with the added benefit of several safety features not found on standard systems. The technology comes at a cost, typically more than $1,500 on most new vehicles. At the moment, the pricing barrier has limited the system to high-end luxury vehicles, keeping it out of the hands of many drivers. As the cost of the technology drops and the system is standardized, ACC will be available in many more models.

Combining features

The latest development in adaptive cruise control is pre-emptive safety systems, which use the system in conjunction with other sensors to monitor the objects in the vehicle’s path and continuously judge the possibility of a collision. These systems provide visual and/or audible warnings to the driver and can tighten the seat belts and ready the air bags in preparation for a possible collision. Pre-emptive safety systems that bring the vehicle to a near or full stop are just becoming available in the U.S. for the 2007 model year, but only for a handful of luxury brands. Some automakers combine adaptive cruise control with other safety features, such as lane-departure warning systems and blind-spot detection, to reduce the likelihood of a collision.

In development

The next generation of pre-emptive safety systems is already being developed, though they are not likely to go into production in this country until at least the 2008 model year. These systems will add a camera that can differentiate between moving objects and stationary items. By the end of the decade, pre-emptive safety systems will also monitor the driver and, based on his or her alertness, tailor its warning responses—for example, by warning sooner if the system sees the driver doesn’t have his eyes on the road. As a result, vehicles will become "smarter," with the ability to recognize potential dangers before an accident occurs.