The National Transportation Safety Board issued an update regarding its investigation of the March highway accident that killed 11 people in Kentucky.
The investigation found that the truck driver was using a cell phone at some point leading up to the accident, but it's unknown whether or not he was using it when the truck departed the roadway. The NTSB would not make a determination about whether the cell phone use was a factor in the accident.

The NTSB said Kenneth Laymon, 45, had been driving a 1999 Freightliner truck with a 53-foot semitrailer southbound on I-65 near Munfordville, when he departed the left travel lane at about a five-degree angle, crossed a 60-foot wide grass median, overrode a four-cable guardrail barrier and struck a 15-passenger van that was traveling in the left northbound lane. The truck continued across the northbound travel lanes, overturning, struck a stone wall, and was engulfed in a post-crash fire.

The van was not involved in any post-crash fire. The 2000 Dodge van was carrying nine adults, two children and an infant. The two children were the only survivors. Eight of the nine adults were not wearing seat belts, NTSB said.

The truck was on a 690-mile trip from Lansing, Mich. To Cullman, Ala. The driver set out from Lansing at about 4 p.m. the previous day. The accident occurred about 13 hours later with about 243 miles remaining in the trip. Investigators are trying to determine how many hours the truck driver was operating the vehicle and if he took any rest periods between his departure from Lansing and the point at which the accident occurred, NTSB said. The truck was not equipped with an electronic onboard recorder, and the driver's logbook was destroyed in the fire.

A toxicology test on the truck driver was negative for alcohol and nine legal and illegal drugs. At this point in the investigation, no medical issues have been found that might have led to a sudden incapacitation of the truck driver.

The NTSB expects to finish the investigation in 12 to 18 months.