Do These Systems Prevent All That Many Car Crashes?

• Recent IIHS study casts doubts on greater safety potential of partial automation systems like adaptive cruise control (ACC), versus automatic emergency braking (AEB), after examining crash and insurance data for a number of recent models.

• The IIHS has noted that some partial automation systems can encourage a false sense of security, "causing drivers to tune out."

• Automatic emergency braking (AEB) is set to become mandatory in all new passenger cars and light trucks by 2029.

Partial automation systems have been on the market long enough not only to be common in high-sticker vehicles, but also to trickle down to very affordable cars.

But do they actually prevent all that many crashes?

The Insurance Institute for Highway Safety (IIHS) isn't so sure.

The IIHS says that insurance data and crash records "offer little evidence" that partial automation systems are actually preventing collisions, citing long-term studies undertaken by the Highway Loss Data Institute (HLDI) and the IIHS.

The study examined certain Nissan and BMW models that have been on the market for some time, and which have been the subject of earlier HLDI research in 2021. The new study, however, now confirms that partial automation systems do not provide additional safety benefits greater than those already offered by features like front automatic emergency braking (AEB), the IIHS claims.

In this instance the IIHS is referring specifically to adaptive cruise control (ACC) systems that use a combination of radar and cameras to keep a vehicle in its lane at a certain speed, slow down in response to traffic up ahead, and to speed back up when the path ahead opens up, in contrast to purely crash avoidance features like automatic emergency braking, lane-departure prevention, or blind-spot warning.

The new study found that in Nissan Rogue models from the 2017 through 2019 model years equipped with forward collision warning and AEB systems saw property damage liability claims that were 8% lower. However, the study saw no such benefit in Nissan Rogues equipped with Nissan’s ProPILOT Assist partial automation system, which includes lane-centering and ACC.

"Changes in claim rates under collision coverage—which is for damage to the insured driver's own vehicle—were small for all the technologies," the IIHS noted.

Likewise, the HLDI's study of BMW and Mini models from the 2013 through 2017 model years equipped with forward collision warning and AEB noted a 13% reduction in property damage liability claim rates and a 7% reduction in collision claim rates. The BMW and Mini models also equipped with ACC on top of forward collision warning and AEB, on the other hand, evidenced a 25% reduction in property damage claims, but no larger difference when it came to collision claims.

"As with the Nissan vehicles, there were no additional statistically significant reductions associated with BMW's Driving Assistant Plus partial automation system," the IIHS noted.

If there is a major caveat to the earlier HLDI study, it's the fact that claims data collected by the HLDI does not show whether in particular accidents the partial automation systems were switched on—the data only shows if they were installed. Additionally, the data does not specify the type of road on which the crashes occurred.

But unlike AEB or front collision warning, ACC has to be actively switched on by a driver.

At first, the IIHS did find larger reductions for vehicles with partial automation, noting front-to-rear crash rates for Rogues with ProPILOT Assist were 62% lower than for cars without crash avoidance systems. Similarly, lane-departure crash rates for Rogues with ProPILOT Assist were found to be 44% lower than for vehicles without such systems.

However, a closer look at that data revealed that the benefits provided by Nissan's ProPilot Assist were essentially the same on low-speed roads, where benefits from partial automation are minimal, as on high-speed roads, where partial automation is most likely to be engaged.

Curiously, the rate differences were the greatest for crashes that occurred in the dark. This suggested to the IIHS that other features, such as higher-rated headlights, could be the difference.

Data uncovered by Jessica Cicchino, senior vice president for research at IIHS, revealed that Rogues with ProPILOT Assist were more likely to feature acceptable-rated headlights than Rogues not equipped with similar systems, which featured headlights rated as "poor" by the IIHS.

According to the IIHS research, acceptable-rated headlights alone reduce single-vehicle nighttime crashes by approximately 15%, in contrast to vehicles whose headlights are rated as "poor." And the rate differences were the greatest in the dark.

Partial automation systems such as adaptive cruise control (ACC) do not make a vehicle self-driving, but they can create an illusion of such a system, the IIHS warns.

"They can't manage many routine roadway features and traffic situations, so drivers have to pay close attention to what's happening on the road and be ready to take over at any time," the IIHS says. "That's a big challenge because the technology can encourage a false sense of security and induce boredom, causing drivers to tune out."

Do you trust systems like adaptive cruise control at highway speeds to use them frequently and without concerns for safety, or do you have some concerns? Let us know in the comments below.