Emailing or texting drivers are an even greater danger on the road than previously thought, according to a new study by the Texas Transportation Institute.

Researchers found that a driver’s reaction time is doubled when distracted by reading or sending a text message.

Reaction times with no texting activity were typically between one and two seconds. However, reaction times while texting were at least three to four seconds.

Worse yet, drivers were more than 11 times more likely to miss the flashing light altogether when they were texting.

Researchers also measured each driver’s ability to maintain proper lane position and a constant speed. They found texting drivers were less able to safely maintain their position in the driving lane or to maintain a constant speed while texting.

The study is the first published work in the U.S. to examine texting while driving in an actual driving environment.

Federal statistics suggest that distracted driving contributes to as much as 20 percent of all fatal crashes, and that cell phones constitute the primary source of driver distraction.

Researchers point to two numbers to illustrate the magnitude of the texting while driving problem: an estimated 5 billion text messages are sent each day in the United States, and at least 20 percent of all drivers have admitted to texting while driving.

Check out this Reuters report for more on the study findings.

This I.I.I. background paper has more on this topic.