IIHS study finds drivers can
be nudged toward safer habits

(November 26, 2024) Drivers who are used to partial automation that switches off when they try to share control over the steering are less willing to steer or put their hands on the wheel in sticky situations, a new study from the Insurance Institute for Highway Safety shows. In contrast, drivers of vehicles with systems that allow some manual steering are more inclined to take an active role.

“These results suggest that small differences in system design can nudge drivers toward safer habits,” said IIHS President David Harkey.

Partial automation systems use cameras and other sensors to keep your car moving down the road in the center of the lane at a speed you select, braking to avoid other vehicles and accelerating again when the way is clear. They are unable to handle many common on-road scenarios, however, so drivers are supposed to pay close attention and be ready to take over at any time. Two recent IIHS studies showed they don’t always do so, despite driver monitoring and attention reminder features.



One way to help keep drivers engaged is by designing systems to allow what’s known as cooperative steering. Partial automation systems designed this way let the driver make minor adjustments within the travel lane without deactivating. Most drivers believe that’s the way their own system works, whether or not that’s the case, the new IIHS study shows. But those whose vehicles really do allow shared control are 40%-48% less likely than the others to say they would keep their hands off the wheel in situations that would make most drivers nervous.

“Those are sizable differences,” said Alexandra Mueller, a senior IIHS research scientist and the lead author of the study. “Although there could be many reasons, one plausible explanation is that systems that switch themselves off whenever the driver steers may make drivers less likely to want to intervene, as it’s a pain to reactivate the system again and again.”

To better understand the impact of system design, Mueller conducted an online survey of 1,260 owners of Ford, General Motors, Nissan/Infiniti and Tesla vehicles equipped with partial automation who regularly use the technology.

Ford’s BlueCruise system and Nissan/Infiniti’s ProPILOT Assist system remain switched on when the driver makes steering adjustments within the lane. General Motors’ Super Cruise system and Tesla’s Autopilot system stop their lane-centering support when the driver gives steering input. Both the Nissan and Tesla systems studied require the driver to keep their hands on the wheel, while the Ford and General Motors systems allow hands-free driving under certain conditions. A current version of ProPILOT Assist that allows hands-free driving wasn’t available in the vehicles owned by the survey participants.

To gauge whether participants understood how their systems responded to manual steering, the research team showed them a video clip depicting the procedure used by the IIHS partial automation safeguards rating program to determine if a system allows cooperative steering. In the video, a driver executed a gentle maneuver to bring the vehicle from one side of the lane to the other. After watching it, the respondents were asked how their system responds when they make a similar steering adjustment.

IIHS tests confirm that this maneuver causes both the Tesla and GM systems to stop their lane-centering support, while the Ford and Nissan systems continue to provide that support but allow the driver to dictate the vehicle’s position in the lane. Once the Tesla system switches off, it must be reactivated by the driver. The GM system can reactivate automatically, but only if the driver first returns the vehicle to the center of the lane and then stops steering. Even then, there can be a lag before it resumes.



Despite those rather stark differences, the respondents tended to think that their systems stayed on and continued to help steer when they executed a maneuver like the one shown in the video, even when they didn’t. However, the actual operating parameters of their systems affected their answers to other survey questions about how they would behave in specific driving scenarios.

For other questions, the participants watched videos that showed some highway-driving scenarios from the point of view of a driver in a vehicle from the same manufacturer as the one they own. For these regular users, it was clear from the dashboard display and other indicators that the partial automation system was switched on.

In the first scenario shown, the driver’s vehicle was traveling down the road in its lane on a clear day with no other vehicles nearby. Nothing of interest happened in the video. It represented a baseline driving situation showing optimal road and traffic conditions for the automation.

In another scenario meant to make the respondent uncomfortable, the driver’s vehicle was traveling in the left lane and coming up behind a large pickup in the right lane. The pickup was towing a trailer with a midsize SUV loaded on it. The pickup and trailer maintained their position in the lane steadily, but the left-side tires of the vehicles were touching the lane line nearest the point-of-view vehicle. The video continued until the point-of-view vehicle had passed the pickup safely.

A third scenario was meant to look alarming. This time, the pickup and trailer veered in and out of the right lane several times as the point-of-view vehicle came up behind. Though the pickup and trailer stopped weaving before the point-of-view vehicle passed, their left-side tires remained on the lane line closest to the overtaking vehicle.

In each scenario, participants were asked if they would steer to one side of the travel lane and whether they would put one or both hands on the wheel.

Under the uneventful driving conditions of the baseline scenario, drivers with cooperative systems were 36% more likely than the others to say they would steer to one side of the travel lane. Owners of both cooperative and noncooperative systems were more likely to say they would want to steer in the two scenarios with the pickup than they were when the road was clear. However, drivers with cooperative systems were 26% and 29% more likely than those with noncooperative systems to say they would steer to one side when passing the steady and weaving pickup, respectively.

Owners of both types of systems responded similarly as to whether they would keep one or both of their hands on the wheel in the baseline scenario. However, when passing the steady pickup and trailer, drivers with cooperative systems were 40% less likely than the others to say they would continue driving with their hands off the wheel. When the pickup was weaving, that percentage increased to 48%.

“These findings suggest that cooperative steering may have an implicit influence on how willing drivers are to take action when the situation calls for it, regardless of how they think their system is designed,” Mueller said.