Karen Cordova, a 17-year-old high school student and part-time supermarket cashier, admits she sometimes texts friends while driving home from work late at night, lonely and bored.

The Arizona teenager knows it's illegal in Phoenix and dangerous. She once almost drifted into oncoming traffic while looking at her phone.

But would a nationwide ban stop Cordova and her friends from texting in their cars? No way, she said.

Nobody is going to listen, Cordova said.

With momentum building in Washington for all 50 U.S. states to outlaw text messaging behind the wheel, there is evidence that the key demographic targeted by such legislation, teen drivers, will not pay much attention.

At least one major study has found that, with mobile devices now central to their lives, young people often ignore laws against using cell phones or texting in the car.

The number of text messages is up tenfold in the past three years and Americans sent an estimated 1 trillion in 2009.

Some police agencies, while strongly in favor of such mandates, say its tough for officers to enforce them.

The California Highway Patrol has handed out nearly 163,000 tickets to drivers talking on hand-held phones since mid-2008. But it has issued only 1,400 texting citations since January in a state of 23 million drivers -- not for lack of trying.

The handheld cell phone is relatively easy for us to spot, we can see when somebody has their phone up to their ear, CHP spokeswoman Fran Clader said.

But with the texting it's a little bit more of a challenge to catch them in the act, because we have to see it and if they are holding it down in their lap it's going to be harder for us to see.

Already 19 states and the District of Columbia ban texting by all drivers, while 9 others prohibit it by young drivers.

TEXTING CAUSES ACCIDENTS

In July, Democratic Senator Chuck Schumer, citing a study that found texting drivers were 23 times more likely to be in an accident, introduced a bill requiring states to prohibit the practice or risk losing federal highway funds.

Since then, Senator Jay Rockefeller has offered his own bill that would achieve the ban through grants to states.

In October, during a three-day conference in Washington on distracted driving, President Barack Obama signed an executive order barring federal employees from texting behind the wheel.

Transportation Secretary Ray LaHood said he would seek to expand that rule to bus drivers and truckers who cross state lines and called the conference probably the most important meeting in the history of the Department of Transportation.

But a much-cited study by the Insurance Institute for Highway Safety found that usage of cell phones for calls and texting in North Carolina actually ticked up slightly after the state banned them for drivers under the age of 18.

A study by the Automobile Club of Southern California found that texting by drivers dropped after the state's law took effect, but it did not break down the data by age.

What I would say is that texting and cell phone devices have become such a component of life for teens and for young people that it's hard for them to differentiate between doing something normal and doing something wrong, said Steven Bloch, senior research associate for the Automobile Club.

The problem is not unique to the United States. In Britain, a public service announcement on texting while driving drew worldwide attention for its extremely graphic imagery.

The spot shows three texting teen girls in a horrific head-on collision with another car, and lingers on shots of their bloodied faces shattering the windshield as a child whose parents have been killed cries for her dead mother to wake up.

In 2007, Phoenix became one of the first U.S. cities to ban texting while driving, although Arizona still has no statewide law.

Out of a group of four high school students interviewed by Reuters in Phoenix, three admitted texting while driving and a fourth said he had stopped only after his cousin caused a serious traffic accident while sending a message.

Cordova's classmate, 17-year-old Anna Hauer, says she often texts her boyfriend when she drives and doubts she or her friends would stop because of new legislation.

By the time they pull you over, the chances are you are going to be done with your text anyway so they can't exactly prove that you were texting, she said.

(Additional reporting by Tim Gaynor in Phoenix and Sinead Carew in New York; editing by Mohammad Zargham)

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