Although California law allows drivers to send voice-activated text messages, a new study suggests they are no less distracting than texts typed by hand.

"I was surprised," said Christine Yager, the Texas A&M Transportation Institute researcher overseeing the study, released late Monday. "I expected less impairment than when one manually sends a text."

The problem, Yager said, is that engaging Siri or other applications can require several commands, and that even hands-free conversation takes a driver's eyes off the road as much as typing out a text. This can lead to lane-swerving and not spotting hazards ahead, including pedestrians and bicyclists.

The study was based on the performance of 43 participants driving 30 mph on a former Air Force base near the Texas A&M campus. Drivers first traveled the course without cellphones, then drove it three more times performing a series of texting exercises -- once using each of two voice-to-text applications (Siri for the iPhone and Vlingo for Android), and once texting manually.

"Siri is very interactive," Yager said. "It's a very back-and-forth process from start to end. Even a short phrase can take a long time."

Researchers measured the time it took each driver to complete the tasks, and also noted how long it took for the drivers to respond to a light which came on at random intervals during the trial runs.

Driver response times were significantly delayed no matter which texting method was used. In each case, drivers took about twice as long to react as they did when not texting.

Yet drivers felt safer when using a voice-to-text application than when texting manually, even though driving performance suffered equally with both methods.

Yager said the findings offer new insight, but only a part of the knowledge that's needed to improve roadway safety.

"Understanding the distracted driving issue is an evolving process, and this study is but one step in that process," she said. "We believe it's a useful step, and we're eager to see what other studies may find."

Other studies are coming. The Insurance Institute for Highway Safety expects to begin looking at the same issue in the future. Spokesman Russ Rader said "the only thing somewhat parallel to this is the study IIHS did in 2005 looking at crash risk associated with cellphone use -- phones used to carry on a voice conversation."

That study found about a fourfold increase in crash risk when conversing on either hands-free or handheld phones. The study was unable to determine whether there was any benefit associated with hands-free devices.

Experimental research using driving simulators indicates that phone conversation tasks, whether using handheld phones or hands-free devices, affect some measures of driving performance. Hands-free phones may eliminate some of the physical and visual distractions of handling phones or dialing, but the cognitive distraction remains.

The average number of text messages sent in the U.S. per day exploded from 31 million in 2002 to 6.1 billion in 2012. In January, the AAA Foundation for Traffic Safety reported that nearly 35 percent of drivers admitted to reading a text or email while driving in the past month and over 26 percent admitted to typing one -- trends likely to continue with the growing burst in smartphone technology.

The Texas A&M study was published during National Distracted Driving Awareness Month, as agencies across the country are sponsoring public awareness campaigns to highlight the dangers of driving distractions, particularly those associated with cellphone use.

"We urge drivers to refrain from texting while driving on any equipment," said Jonathan Adkins of the Governors Highway Safety Association. "The safest thing to do is focus one's attention solely on driving."

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