Cooperative Adaptive Cruise Control (CACC): A Path Toward Greater Road Efficiency

In 1945, a blind engineer named Ralph Teetor invented cruise control, the popular automobile feature that most modern citizens can’t live without. Since that time, cruise control systems and their technology have evolved into even “smarter” technologies called adaptive cruise control (ACC).

ACC employs radar sensor technology to automatically adjust a vehicle’s speed based on its surroundings. In support of collision avoidance, a car with ACC automatically slows down if it senses that the car in front of it is too close.

Patented by General Motors in 1991, this technology, which was once reserved for luxury vehicles alone, is far more common, having been embraced by the likes of Honda, Subaru and Kia Motors. Information Handling Service (IHS), an industrial analyst group, predicts that by 2020, at least seven percent of the new cars on any given lot will sport ACC.

Extending adaptive cruise control capabilities

Cooperative adaptive cruise control (CACC) adds another layer of complexity and sophistication to ACC functionality. In lay terms, vehicles equipped with CACC “talk” with each other via wireless V2V technology.

According to California Partners for Advanced Transportation Technology (California PATH), the connected nature of CACC vehicles allows them to “follow more closely, accurately, and safely, with braking and accelerating done cooperatively and synchronously.”

This is possible because cars with CACC don’t just sense the presence of one another; they communicate with one another. In short, CACC vehicles do the following:

  • maintain a consistent speed when unobstructed (like any cruise control)
  • adjust distance from other vehicles based on radar sensor data (like ACC)
  • receive GPS data from surrounding vehicles and share it with others (the CACC innovation)

Selecting the gap

Both ACC and CACC technology allow drivers to manually select the gap of time they prefer to maintain between their own vehicle and others on the road.

With ACC, the minimum time gap is approximately one second, whereas with CACC, that figure dips as low as 0.6 seconds.

Theorists believe that a shorter time gap between cars would lead to a “managed lane” effect, in which traffic flow could be more effective, reducing traffic congestion by encouraging commuters to adhere to more predictable traveling schedules.

ACC & CACC: Weighing the pros and cons

CACC is a relatively new extension of ACC, and as such, is not yet widely available to the public. Researchers are currently weighing the pros and cons to see if this new technology is suitable for public roads. Here are some advantages and disadvantages to consider regarding each of these technologies:

ACC advantages

  • ACC is less of a leap from traditional cruise control than CACC and, therefore, is easier to gain consumer buy-in. AAA reports that current owners “have a very high opinion of it, with 76-93 percent of survey respondents reporting that they would buy the system again.”
  • AAA reports that “[N]early half of respondents said that the system helps relieve stress,” and “[a]bout a third of respondents said that the system made them a safer driver.”

ACC disadvantages

  • Feedback information from the ACC system is relative and based on the behavior of surrounding vehicles. It does not, however take into account potentially unsafe driving habits of those vehicles.
  • ACC allows vehicle-to-vehicle (V2V) adjustments but not vehicle-to-infrastructure (V2I) adjustments.
  • ACC has a negligible effect on lane capacity because of the longer time gaps involved.

CACC advantages

  • CACC technology increases lane capacity by decreasing time gaps between cars.
    • Increased lane capacity results in lower fuel consumption, greater fuel efficiency and other environmental benefits.
  • CACC allows for advancements in the safety of complete traffic systems on the whole, including lights and other components of the infrastructure.

CACC disadvantages

  • Having only some vehicles with CACC capability defeats the purpose, since the feature depends on V2V communication.
  • The connected nature of CACC raises some questions about user privacy, as well as vulnerability to hackers and other scammers.
  • In the event of a collision involving CACC vehicles, liability would be difficult to determine.

Additional considerations pertaining to both technologies are that they are currently cost prohibitive, and neither has a long enough history to have garnered much by way of statistics on safety usage.

 Waiting on legislation

ACC technology employs the same radar technology that will one day be a staple component of self-driving cars, according to auto expert Sridhar Lakshmanan of the University of Michigan-Dearborn. While the prospect of autonomous automobiles is certainly an exciting one, the majority of Americans are still waiting for state legislation to define and legalize the technology. Still, a handful of states have succeeded in making political advances toward the testing and funding of such cars, including Illinois, New York and Texas.

When Teetor invented the first cruise control system more than 70 years ago, we have no way of knowing if he foresaw his invention evolving into a technology where cars and trucks “converse” with one another. As with so many things, what was once only science fiction is now finding a place in reality. For now, full CACC technology remains just out of reach for the general public, as researchers and experts continue to explore both its benefits and drawbacks.