Transportation Secretary Ray LaHood Wednesday called distracted driving a serious epidemic with more than 5,800 annual U.S. traffic deaths tied to motorists who failed to keep their eyes on the road.

LaHood opened a two-day conference exploring research on cellphone use and text messaging while driving as well as other topics that can divert the attention of motorists.

To put it plainly, distracted driving is a menace to society and it seems to be getting worse every year, LaHood said, adding that it was an extraordinarily serious epidemic.

Figures released at the conference by the National Highway Traffic Safety Administration (NHTSA) showed more than 5,800 distracted driving deaths and 515,000 injuries last year.

The fatality figures released by the government on distraction did not break down crashes by specific driver behavior. Broadly, safety officials identified cellphone use, texting, eating, talking to passengers and manipulating radio or vehicle controls as distractions.

The proportion of deadly accidents tied to distracted driving climbed from 11 percent in 2004 to 16 percent in 2008, according to the figures culled from police reports. By comparison, drunken driving accounted for roughly 30 percent of all fatalities.

Drivers under 20 years old were involved in 16 percent of distracted-driver fatal crashes. Those ages 20 to 29 accounted for another 12 percent.

The figures were significant but may not show the full problem since identifying distraction as a cause of crashes, especially in fatal accidents, can be difficult, transportation officials and safety experts acknowledged.

We're all trying to look at this as carefully as possible, said Adrian Lund, president of the Insurance Institute for Highway Safety. There are some questions we need to answer.

For instance, Lund's group, which is funded by insurance companies and analyzes vehicle safety performance and other trends, said there is little overall information specifically on cellphone use and crashes -- a major target of states and federal officials.

There are also general safety contradictions as overall U.S. highway fatalities have declined. Police reports on crashes, an indicator of serious accidents, and auto-related property claims have also gone down.

We're just uncertain how big the problem is, Lund said.

A separate survey released Wednesday by the Transportation Department showed 6 percent of drivers, or 812,000 people at any one time, used hand-held cellphones while driving in 2007. One percent used other hand-held devices to send text messages or read.

Auto manufacturers, the wireless industry, lawmakers and other groups support state and local efforts to ban texting while driving, but outlawing cellphone use behind the wheel has less support. Congress is also considering legislation to ban texting while driving.

(Reporting by John Crawley, editing by Alan Elsner and Bill Trott)