In the moments before his tractor-trailer veered across the median on Interstate 65 in Kentucky, the 45-year-old driver of the big rig was on the phone.

The truck slammed into an oncoming passenger van, killing both drivers and nine other people traveling in the van. Two children in the van, who were in child seats, survived the crash.

The National Transportation Safety Board said the March 2010 accident was the worst highway crash to occur in Kentucky in a generation.  The  NTSB today recommended a ban on the use of cellphones by all commercial drivers.

The proposal is the most comprehensive ban on hand-held and hands-free devices that the board has issued. The NTSB, which cannot require a ban, sent its recommendation to both the states and the federal government.  

If enacted, the ban would affect 3.7 million drivers, according to the NTSB. “Changing behavior can start right now, for drivers of big rigs, but also for the rest of us,” NTSB Board Chairman Deborah Hersman said. “When you are at the wheel, driving safely should be your only focus.

“I can tell you that commercial vehicle drivers are not going to embrace this,” Hersman added, “but we are not here to be popular.”

The Insurance Institute for Highway Safety says the real challenge with all cellphone bans is enforcement. And the Governors Highway Safety Association (GHSA) suggests that a ban put in place by companies, not the government, would be met with more success. Both groups say any ban on mobile devices will be more effective if drivers know their jobs are dependent on not using phones while they drive.

“Texting or talking on the phone while driving can turn deadly in a matter of seconds, particularly when a big rig or a bus is involved,”  U.S. Transportation Secretary Ray LaHood said in a statement to ABC News. “That is why the U.S. Department of Transportation has already banned commercial drivers from texting while driving and has rulemaking underway to ban hand-held cellphone use. There is no call or text message that is worth risking  lives.”

In its findings on the Kentucky accident, the NTSB said, “the probable cause of this accident was the truck driver’s failure to maintain control of the truck-tractor combination because he was distracted by the use of his cellular telephone.”

“Distraction is becoming the new DUI,” NTSB board member Robert Sumwalt said. “It is pervasive. It is in all modes of transportation.”

Data collected by the NTSB showed that the driver of the tractor-trailer was texting and making calls “frequently” in the hours leading up to the accident. The NTSB documented 69 calls or texts made by the driver while driving in the 24-hours prior to the accident. And the board noted, “In the minutes before the 5:14 a.m. crash, the driver made three phone calls, the last one at 5:14.”

“We do know that [the driver] was engaged in operating his cellphone,” said Dennis Collins, a human performance expert with the NTSB who presented data during the board meeting. “That distraction lead to the accident.”

No states have bans in place for all cellphone use in cars, based on data posted on the GHSA web site. But 34 states ban text messaging for all drivers and nine states ban hand-held cellphone use. Kentucky, where the accident occurred, bans text messaging but not the use of hand-held cellphones, according to GHSA.