Few voice-activated, handsfree driving systems are looking good Tuesday after AAA released a major study that accuses them all of increasing our levels of distraction behind the wheel.

The least distracting in-car system, it turns out, is Toyota's Entune. The most distracting: Chevy's MyLink. And the absolute worst offender when it comes to voice-activated systems that overtax our brains? Apple's Siri.

See also: 6 Tech Tools to Tackle Distracted Driving

The study, named "Mental Workload of Common Voice-Based Vehicle Interactions across Six Different Vehicle Systems" [PDF], didn't skimp when it came to measuring distracted driving. It stuck 36 participants (18 male, 18 female) behind the wheels of six cars with voice-activated infotainment systems, asking them to perform multiple tasks and navigate a nine-minute driving course. It pointed cameras at the drivers, measured their brain activity and heart rate, had a researcher in the passenger seat evaluate their reactions, and asked the drivers themselves to fill out a questionnaire afterwards.

The conclusion, in a sentence: "Common voice tasks are generally more demanding than natural conversations, listening to the radio, or listening to a book on tape," the AAA Foundation for Traffic Safety researchers wrote.

This is the latest in a series of studies from the same researchers looking at distracted driving. Here's how the various forms of car-based voice-activated commands stack up in mental distraction:

Image: AAA Foundation

You read that right — using Siri is more mentally taxing than the most poorly-designed voice-activated in-car screen menu.

As for the pure in-car systems, the researchers found a correlation between the amount of time it took to complete a task via voice commands (such as switching from CD to a radio station, or calling a contact in your address book) and the amount of distraction involved. So here's how each in-car system stacks up in terms of time taken:

Image: AAA Foundation

The need to address the problem is urgent, the AAA says. There are more than 9 million cars and trucks on the road with voice-activated infotainment systems right now; that number is expected to rise to 62 million by 2018. The more these systems tax our brain, the less we're seeing the road — even if we're looking right at it.

"Police accident investigative reports are filled with comments like the 'looked, but did not see,'" said Peter Kissinger, president and CEO of the AAA Foundation. "That's what drivers tell them. We used to think they were lying, but now we know that's actually true."