The systems let drivers do things like tune the radio, send a text message, or make a phone call while keeping their eyes on the road and their hands on the wheel, but many of these systems are so error-prone or complex that they require more concentration from drivers rather than less, according to studies released Tuesday by the AAA Foundation for Traffic Safety and the University of Utah. The second study tested the Apple iPhone's Siri voice system to navigate, send texts, make Facebook and Twitter posts, and use the calendar without handling or looking at the phone. Apple and Google are working with automakers to mesh smartphones with infotainment systems so that drivers can bring their apps, navigation and music files into their cars. The systems were tested by 162 university students and other volunteers in three settings: a laboratory, a driving simulator and in cars while driving through a Salt Lake City neighborhood. "What we continue to see from customers is that they demand this level of technology in their vehicles, that access to music and access to calls is now a critical part of the driving experience and so we're looking at innovative ways to provide that," said Chevrolet spokeswoman Annalisa Bluhm. The National Highway Traffic Safety Administration, which regulates vehicle safety, has issued guidelines to automakers for dashboard systems and is working on similar guidelines for cellphones and voice-activated systems, but the guidelines are voluntary.