Texting or emailing while driving is more dangerous than previously thought, according to a new study of the behavior.
"Essentially texting while driving doubles a driver's reaction time," Christine Yager, who led the study at Texas A&M University's Texas Transportation Institute, told Reuters on Wednesday.
"That makes a driver less able to respond to sudden roadway dangers."
For the study, 42 drivers between the ages of 16 and 54 drove on an 11-mile test track course while sending or receiving text messages, and drove it again while focusing completely on the road.
Drivers were asked to stop when they saw a flashing yellow light, and their reaction times were recorded, Yager said.
The typical time it took a driver who was not texting to respond to the flashing light was one to two seconds. But when the driver was texting, the reaction time extended to three to four seconds, and the texting motorist was 11 times more likely to miss the flashing light altogether.
Yager said the reaction time was the same whether the driver was typing a message or reading one.
"The act of reading and writing a text message are equally impairing and equally dangerous," she said.
Yager said the research differed from previous studies in that it involved participants driving actual vehicles, not driving simulators.
A previous well-respected study done on a lab simulator showed drivers reacted in less than one second when they were not texting and to stimulus while texting in 1-2 seconds, Yager said. The 3-4 second lag time in the actual driving study is significant because in that period at highway speeds one can travel the length of a football field, she said.
Institute spokesman Rick Davenport said texting drivers were less able to stay in their lane and unable to maintain a constant speed.
The closed course contained no other vehicles, no pedestrians, and no hills, Davenport said.
Texting drivers were more likely to swerve in their lane, Yager said.
"Even though we had participants drive at 30 miles an hour with very wide lanes on the test track, we still had many close calls," she said.
"We had participants strike barrels, and it is very scary to think that this is happening on our public roadways."
Yager said the study findings extend to other driving distractions, such as checking e-mail and Facebook.
US Transportation Department statistics indicate distracted driving contributes to as much as 20 per cent of all fatal crashes, and that cell phones are the primary source of driver distractions.
At least one in five motorists has admitted to texting while driving, according to the department.
Text messaging while driving is banned in 34 states and the District of Columbia, according to the Insurance Institute for Highway Safety. An additional seven states ban texting while driving for some motorists, such as those under 18 or bus drivers. In addition, many cities and counties have banned texting while driving.