Appropriate driver responses and acceptance of crash avoidance technologies are critical to their success. If drivers don't trust the systems or find them annoying or not useful, they may disable them. Similarly, if drivers experience warnings but don't understand them, are overwhelmed by them, or don't take an appropriate corrective action, then the systems will be ineffective.
Interpreting warnings from multiple systems may be confusing or even distracting for some drivers. Many drivers involved in lane departure crashes are asleep or otherwise incapacitated, which can limit their ability to respond to lane departure warning and lane-keeping support systems (Cicchino & Zuby, 2017; Wiacek et al., 2017).
Partial automation may require additional training. Drivers need to know when automation is available, how to use it and how to take control when automation is no longer available or if it fails. Experimental studies have shown that drivers can lose sight of what automated systems are doing, fail to notice when something goes wrong, and have trouble taking control again (Endsley & Kiris, 1995; Gold et al., 2016; German Insurers Accident Research (UDV), 2016; Haslbeck & Hoermann, 2016; Lee & See, 2004; Merat et al., 2014; Mueller et al., 2020; Ruscio et al., 2015; Wickens et al., 2004; Zeeb et al., 2016).
Systems need to be turned on to be effective. Observations at dealerships of seven automakers in 2016 found that front crash prevention systems were activated in 93 percent of the vehicles observed that arrived for service, and nearly 100 percent of the blind spot detection and rear-cross traffic alert systems were turned on (Reagan at al., 2018). Activation of lane departure warning and lane keeping-support systems were much lower at 52 percent. Lane departure systems that warned by vibration were more likely to be activated than those that beeped, and lane keeping assistance systems were more likely to be turned on than warning-only systems.
Automated systems also can't be effective unless they are used. IIHS research shows that driver acceptance of lane centering and adaptive cruise control systems can vary considerably by vehicle. Drivers report that systems that make smooth, gradual speed or steering adjustments improve the experience (Kidd & Reagan, 2018, Reagan et al., 2020).
One concern is that drivers might rely on crash avoidance systems too much and feel freer to look away from the road or take other risks. However, in IIHS surveys of owners of vehicles with various technologies, many owners reported safer driving habits with the systems — for example, using turn signals more often with lane departure warning (Braitman et al., 2010; Eichelberger & McCartt, 2014; Cicchino & McCartt, 2015; Eichelberger & McCartt, 2016). Fewer owners reported potentially unsafe behavior, such as waiting for an alert before braking or allowing the vehicle to brake for them at least some of the time.
An Institute naturalistic study monitored teens who drove vehicles with and without a suite of prototype collision avoidance systems, including forward collision warning and lane departure warning. When teens drove with the systems, turn signal use increased and lane drifts decreased, but the teens also followed other vehicles at close distances more often (Jermakian et al., 2017).
Partially automated systems, such as Level 2 driving automation, might have unintended consequences, as drivers become disengaged because the vehicle is handling more of the driving. System misuse has already been implicated in fatal crashes (NTSB, 2017; NTSB, 2019).
In addition to driver challenges, the technology itself can have limitations. For example, lane departure warning systems use sensors to register lane markings or the road edge, which may be problematic on roads that aren't well marked or are covered with snow. Sensors may not function well in low light or inclement weather. Some systems only work at certain speeds.
Crash avoidance technologies can also have the unintended consequence of increasing some crash types while reducing others. The Institute's research on the effects of front crash prevention on police-reported crashes found that vehicles with forward collision warning and automatic braking had a 20 percent higher rate of being rear-ended than vehicles without the systems (Cicchino, 2017). However, vehicles with forward collision warning alone or low-speed autobrake had lower rates of being rear-ended than vehicles without.