State laws that banned texting while driving significantly reduced the number of teens using their cell phones behind the wheel, but a new study found that nearly one-third still admitted to engaging in this risky behavior.

Texting has been found to be more dangerous than driving while intoxicated as it increases the risk of crash nearly 20-fold. Adolescents already are at increased risk of having a serious car accident because they are relatively inexperienced drivers, and texting while driving markedly elevates that risk.

For the study, researchers collected and analyzed data from the 2011 and 2013 Youth Risk Behavior Surveillance surveys to determine whether state laws banning texting while driving were effective in changing teens' behavior. They also looked at the relationship between driver age and experience on texting while driving.

Fourteen states passed laws banning texting while driving between 2011 and 2013. Responses from 1,566 teens in 2011 and 1,353 teens in 2013 showed the texting rate dropped significantly from 43.1 percent of teens in 2011 when no bans were in effect to 30.6 percent of teens in 2013 when texting while driving was illegal.

"Despite public health campaigns and laws banning texting while driving in most states, texting while driving was four times more common among U.S. high school students than driving while under the influence of alcohol (41.4 percent vs. 10 percent)," Alexis Tchaconas, principal investigator of the study, said in a statement. "Although laws that ban texting while driving appear to be somewhat effective in reducing this dangerous behavior by teen drivers, much more needs to be done to effectively eliminate this major distraction."

The second analysis showed that texting while driving was nearly five times higher among experienced drivers (defined as more than one year older than the age of initial driver license eligibility in their state) than new drivers. In addition, the risky behavior was more common among 16-year-olds than 15-year-olds.

"Tragically, smartphones still allow teens to do stupid things while driving a car," Andrew Adesman, senior investigator of the study, said in a statement. "It is unfortunate that the smart engineers that make these phones don't restrict or disable texting features when the phone is traveling more than 5 mph. As a parent and as a pediatrician, I would love to see some parental controls built into smartphones so that teenagers cannot be distracted while driving."

The findings will be presented at the Pediatric Academic Societies (PAS) annual meeting in San Diego.