As with many improvements to automobiles along with driver benefits, there is often an unintended negative consequence. This is true for some of the automated systems now available on the newer vehicles, according to a recent study by the Insurance Institute for Highway Safety in the December edition of Status Report. Drivers reportedly fidgeted with electronics and took their hands off the steering wheel more often as they developed more trust in automated systems.

To investigate how experience with automation affects driver disengagement, the researchers studied the driving behavior of 20 Massachusetts-based volunteers over a month’s time as they gained familiarity with advanced driver assistance features, examining how often they removed both hands from the steering wheel or took their attention away from the road to do things like use their cellphone or adjust the controls on the vehicle’s console.

One group of 10 drove a Land Rover Range Rover Evoque equipped with adaptive cruise control (ACC), which automatically keeps the vehicle traveling at a speed chosen by the driver while maintaining a pre-established following distance. Another 10 drove a Volvo S90 with both ACC and Pilot Assist, a partially automated system that combines ACC with lane-centering technology that keeps the vehicle positioned laterally in the travel lane.

When the drivers first received the vehicles, there was little or no difference in how frequently they showed signs of disengagement, whether they were driving manually, using ACC or using Pilot Assist. After a month, however, they were substantially more likely to let their focus slip or take their hands off the wheel when using automation, and the impact of Volvo’s Level 2 system was more dramatic than that of ACC alone, says IIHS Senior Research Scientist Ian Reagan, lead author of the study.

“Drivers were more than twice as likely to show signs of disengagement after a month of using Pilot Assist compared with the beginning of the study,” Reagan says. “Compared with driving manually, they were more than 12 times as likely to take both hands off the wheel after they’d gotten used to how the lane centering worked.”

Pilot Assist and similar systems like Tesla’s Autopilot, Cadillac’s Super Cruise and Mercedes-Benz’s Intelligent Drive are not designed to replace the driver. They have trouble negotiating many common road features, so the driver must be in control at all times. However, with the automation managing steering and speed — quite well in some cases — it’s easy for the driver to lose focus.

“This study supports our call for more robust ways of ensuring the driver is looking at the road and ready to take the wheel when using Level 2 systems,” says Reagan. “It shows some drivers may be getting lulled into a false sense of security over time.” So, if your next vehicle (or your current one) comes with level 2 systems, be aware of the potentially dangerous trap that you could experience if you are not on top of your driving.