Siri and other voice-activated systems can cause potentially unsafe mental distractions lasting several seconds while driving, according to a new research study by the AAA Foundation for Traffic Safety. Siri’s score of 3.4 on the five-point scale is considered more distracting than Google Now’s 3.0 score, but less distracting than Microsoft Cortana, which received a 3.8 rating.

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AAA‘s mental distraction rankings also included vehicles, ranging from the least distracting Chevy Equinox at 2.4 to the Mazda 6 at 4.6, which is nearly the highest level of cognitive distraction. The study found that mental distractions can persist for as long as 27 seconds after using hands-free or voice-activated systems, as drivers readjust to the task of driving.

“The lasting effects of mental distraction pose a hidden and pervasive danger that would likely come as a surprise to most drivers,” said Peter Kissinger, President and CEO of the AAA Foundation for Traffic Safety. “The results indicate that motorists could miss stop signs, pedestrians and other vehicles while the mind is readjusting to the task of driving.”

Researchers found that potentially unsafe levels of mental distraction can last for as long as 27 seconds after completing a distracting task in the worst-performing systems studied. At the 25 MPH speed limit in the study, drivers traveled the length of nearly three football fields during this time. When using the least distracting systems, drivers remained impaired for more than 15 seconds after completing a task.

AAA’s mental distraction rankings while driving are broken down into five categories:

Category 1: About the same as listening to the radio or an audio book
Category 2: About the same as talking on the phone
Category 3: Equivalent to sending voice-activated texts on an error-free system
Category 4: About the same as uploading social media
Category 5: Highly challenging, scientific test designed to overload a driver’s attention

The study did not include the latest in-dash systems such as CarPlay or Android Auto.

The AAA Foundation for Traffic Safety published Phase I and Phase II of this study over the past few years. In the second phase, the foundation found Siri’s high complexity and low intuitiveness resulted in some of the highest levels of mental distraction compared to other in-car tasks such as adjusting the radio or navigating complex menus.