There are several names and acronyms used to describe systems that are designed to assist drivers in avoiding collisions, such as advanced driver assistance systems (ADAS), crash avoidance systems (CAS), and collision warning systems (CWS). The primary goal of any crash avoidance system is to prevent or mitigate crashes by detecting a conflict and alerting the driver, and, in many systems, also automatically applying the brakes.

https://evidencesolutions.com/human-factors-articles/an-emerging-challenge-is-collision-avoidance-technology-better-than-a-human-driver

Legal Cases Involving Crash Avoidance Technology

The National Transportation Safety Board (NTSB) predicts that semi-autonomous crash avoidance technology may prevent or lessen the severity of injuries in 93.7 percent of crashes involving passenger vehicles and 79.0 percent of crashes in which the striking vehicle is a tractor-trailer.[1]  Thus, many cases have been filed in which the Plaintiff sues a vehicle manufacturer for not equipping their vehicle with readily available safety technology or for making it optional (or more expensive) for a buyer.  In those cases, the allegations may hinge on the argument that the collision would not have occurred if a particular CAS technology had been installed in the striking vehicle.  These assertions are based on a presumption that CAS technology would have performed better than the human driver during the collision.  However, there are technological limitations to any CAS technology, and there are some situations where human drivers can and do outperform CAS technology.  Therefore, when evaluating an assertion that a CAS would have prevented a collision from occurring from a human factors perspective, it is important to fully understand the capabilities and limitations of both the specific CAS technology and the human driver.  

Limitations of Collision Avoidance Systems

Importantly, the safety benefit predicted by the NTSB assumes that the installed CAS system is a “perfect system capable of providing sufficiently early warnings or initiation of automatic emergency braking (AEB)”.1  However, a “perfect system” does not exist when considering that humans must interact with and respond to the warning information provided by a CAS technology (e.g., forward collision warning) and/or any actions taken by a CAS technology (e.g., automatic braking, steering correction).  To that end, the effectiveness of any CAS technology in preventing crashes must be balanced against the dangers of incorrect or false activation of warnings and automatic braking, as well as driver annoyance.  For example, a forward collision warning (FCW) system that is required to provide alerts such that all drivers are able to avoid rear-end crashes in all possible situations would necessarily provide alerts to a large number of drivers in situations that drivers did not consider alarming. The resulting high number of nuisance alerts may cause drivers to ignore the FCW alerts and thus reduce system effectiveness substantially [2]

In addition, drivers who are only presented with a warning (because AEB is not available or does not activate) do not simply start braking as soon as the FCW alert is activated.  That is because drivers who receive an FCW alert must look forward, assess the threat, and decide whether to hit the brake pedal or continue driving at the same speed, which takes some time.  In addition, studies have shown that in some circumstances (e.g, drivers who are using adaptive cruise control), many drivers are on the brake in response to a potential collision threat before the CAS even initiates an FCW alert or AEB response.[3]

Human Factors Expert Analysis

Taken together, when evaluating whether a CAS would have prevented a specific collision from occurring, an expert should consider the human driver’s capabilities and limitations when interacting with a CAS.  That is because the human driver’s ability to interact effectively with any semi-automated CAS technology directly affects whether a CAS would have prevented a collision.  In addition, an expert should consider whether the human driver in the incident collision performed better or worse than the CAS technology would have under similar circumstances.  This requires an analysis of the striking driver’s actions to determine if the driver was reasonably attentive, if the driver perceived and responded to the situation in a reasonable amount of time, and, perhaps most importantly, if the driver responded before the CAS would have issued an FCW alert or activated AEB.

While CAS are becoming increasingly common and offer significant potential to reduce the frequency and severity of motor vehicle collisions, they are not inherently superior to human drivers in all situations. Moreover, no CAS is a "perfect system."  Determining whether a CAS would have prevented a specific incident requires a thorough analysis that considers both the system’s capabilities and the human driver’s behavior.