SALT LAKE CITY, UT — A new study confirms that the reaction time of cell phone users slows dramatically, increasing the risk of accidents and tying up traffic in general, and when young adults use cell phones while driving, they're as bad as sleepy septuagenarians, according to a report by LiveScience on January 30. "If you put a 20-year-old driver behind the wheel with a cell phone, their reaction times are the same as a 70-year-old driver who is not using a cell phone," said University of Utah psychology professor David Strayer. "It's like instantly aging a large number of drivers." The study is detailed in the winter issue of the quarterly journal Human Factors. Cell phone distraction causes 2,600 deaths and 330,000 injuries in the United States every year, according to the journal's publisher, the Human Factors and Ergonomics Society. The reason is now obvious: Drivers talking on cell phones were 18-percent slower to react to brake lights, the new study found. In a minor bright note, they also kept a 12-percent greater following distance. But they also took 17-percent longer to regain the speed they lost when they braked. That frustrates everyone. "Once drivers on cell phones hit the brakes, it takes them longer to get back into the normal flow of traffic," Strayer said. "The net result is they are impeding the overall flow of traffic." Strayer and his colleagues have been down this road before. In 2001, they found that even hands-free cell phone use distracted drivers. In 2003 they revealed a reason: Drivers look but don't see, because they're distracted by the conversation. The scientists also found previously that chatty motorists are less adept than drunken drivers with blood alcohol levels exceeding 0.08. Separate research last year at University of Illinois at Urbana-Champaign supported the conclusion that hands-free cell phone use causes driver distraction. "With younger adults, everything got worse," said Arthur Kramer, who led the Illinois study. "Both young adults and older adults tended to show deficits in performance. They made more errors in detecting important changes and they took longer to react to the changes." The impaired reactions involved seconds, not just fractions of a second, so stopping distances increased by car-lengths. The latest study used high-tech simulators. It included people aged 18 to 25 and another group aged 65 to 74. Elderly drivers were slower to react when talking on the phone, too. The simulations uncovered a twofold increase in the number of rear-end collisions by drivers using cell phones. Older drivers seem to be more cautious overall, however. "Older drivers were slightly less likely to get into accidents than younger drivers," Strayer said. "They tend to have a greater following distance. Their reactions are impaired, but they are driving so cautiously they were less likely to smash into somebody." But in real life, he added, older drivers are significantly more likely to be rear-ended because of their slow speed. Other studies in the journal found:

• Telephone numbers presented by automated voice systems compete for drivers' attention to a far greater extent than when the driver sees the same information presented on a display.
  

• Interruptions to driving, such as answering a call, are likely to be more dangerous if they occur during maneuvers like merging to exit a freeway.
  

• Things could get worse. Wireless Internet, speech recognition systems, and e-mail could all be even more distracting.