In-dash phone systems are overly complicated and prone to errors, the study found, and the same is true for voice-activated functions for music and navigation.
A companion study also found that trying to use Siri — the voice control system on Apple phones — while driving was dangerously distracting. Two participants in the study had virtual crashes in an automotive simulator while attempting to use Siri, the study's authors reported.
"We already know that drivers can miss stop signs, pedestrians and other cars while using voice technologies," said Bob Darbelnet, chief executive of AAA. "We now understand that current shortcomings in these products, intended as safety features, may unintentionally cause greater levels of cognitive distraction."
The studies measured cognitive distraction — the mental workload required of a task — as opposed to the visual distraction, caused by drivers taking their eyes off the road, or physical distraction, such as reaching for a cellphone or brushing hair. The researchers used special test vehicles, heart-rate monitors and other equipment to measure how much mental distraction the systems generated. The systems were rated on a five-point scale, with five representing the most distracting.
Chevrolet's MyLink system, which the researchers tested in a 2013 Chevy Cruz Eco, scored the worst of the six systems from auto manufacturers.
It generated a distraction rating of 3.7 on the study's scoring protocol — compared with 2.45 for a hand-held cellphone. Three of the other systems rated as more distracting than a hand-held phone: Chrysler's UConnect System, 2.7; Ford's Sync with MyFord Touch system, 3.0; and Mercedes' Command system, 3.1.
Only Toyota's Entune, at 1.7, and Hyundai BlueLink, 2.2, scored better.
But the report doesn't recommend using a hand-held cellphone, either.
"The primary task should be driving. Things that take your attention away make you a poor driver," said University of Utah psychology professor and study leader David Strayer. "Even though your car may be configured to support social media, texting and phone calls, it doesn't mean it is safe to do so."
The voice-based systems distracted drivers because they are too complex and made too many errors in recognizing voice commands, according to the research.
"Drivers were cursing the systems out," Strayer says. "If you want to buy one of these cars, make sure you can actually use the voice-based technology before you leave the lot."
Automakers discounted the findings, noting that the research did not document that cognitive distraction leads to crashes. Conversely, physical activities, such as reaching for a phone, texting or reading emails while driving do create distractions that cause collisions.
A National Highway Traffic Safety Administration study released last year concluded that physical and visual distractions triple the risk of crashes.
That's why Chevrolet installs a voice-command system and steering wheel button controls in its vehicles, said Annalisa Bluhm, a GM spokeswoman.
"We feel that hands on the wheel and eyes on the road is critical to safe vehicle operation," Bluhm said.
Toyota said the study did not show a link between cognitive distraction and car crashes.
"The results actually tell us very little about the relative benefits of in-vehicle versus hand-held systems; or about the relationship between cognitive load and crash risks," said Mike Michels, a Toyota spokesman.
Still, Toyota said it supported AAA's commitment to studying the cognitive demands of various tasks and helping prevent distracted driving incidents. The automaker said it was pleased to score well in the study.
The study of cognitive distraction is still evolving, said AAA spokeswoman Nancy White.
"However, with more than 3,000 people killed a year due to driver distraction, it's what we don't know about distraction that should be of concern," White said.
White noted that the research proves that automakers and phone-makers can and should design systems that are less complex and more intuitive — and safer.
Siri was notable for producing "different responses to seemingly identical commands," the researchers wrote.
In some instances, the Apple system required exact phrases to accomplish a specific task. It wouldn't understand subtle deviations from that phrasing. It also required drivers to start over when it made a dictation error in a message, because it offered no way to edit.
"Siri also made mistakes such as calling someone other than the desired person from the phone contact list," the study said. "Some participants also reported frustration with Siri's sarcasm and wit."
Apple said the study did not test CarPlay or Siri Eyes Free, which the company has designed for drivers to access features and apps they want in the car with minimized distraction. However, CarPlay is a new system that is just rolling out in some 2015 model year cars. Siri Eyes Free also is fairly new, only widely available in some car brands starting in the 2014 model year.