Four veterans were killed in the resulting collision in Midland on Thursday. Sixteen people were injured.
Dale Andrew Hayden was driving one of two flatbed trucks carrying wounded veterans and their loved ones in the procession to honor the war heroes, said Hal Brockett, Hayden's attorney.
"Words can't express the sorrow and remorse for the people who got hurt and killed," Brockett said in an interview Tuesday.
Investigators say the float began crossing the train tracks even though warning bells were sounding and the crossing lights were flashing. A Union Pacific train travelling at more than 60 mph ran into the truck as the occupants scrambled to jump to safety.
Hayden, who had a military career spanning more than three decades, now works as a truck driver for Smith Industries, an oilfield services company. Brockett said the company has placed Hayden on medical leave.
Hayden is "kind of catatonic" and not ready to be interviewed, Brockett said.
"He's just very much in shock," the lawyer said.
The San Antonio Express-News first identified Hayden as the driver.
Federal investigators on Tuesday plan to re-enact the events that led to the collision.
According to the National Transportation Safety Board, the railroad crossing warning system was activated 20 seconds before the accident, and the guardrail began to come down seven seconds after that.
But some Midland residents have said there isn't enough time between when the signal begins and the trains arrive. They say guardrails aren't completely down by the time a train comes by.
The Union Pacific freight train heading to Louisiana was estimated to be going at 62 mph at the time of the crash.
The veterans had been invited to Midland, a transportation and commerce hub in the West Texas oilfields, for a three-day weekend of hunting and shopping in appreciation of their service. A local charity, Show of Support, had organized the trip, parade and other festivities. Show of Support officials have declined to identify the driver.
Killed were Marine Chief Warrant Officer 3 Gary Stouffer, 37; Army Sgt. Maj. Lawrence Boivin, 47; Army Sgt. Joshua Michael, 34; and Army Sgt. Maj. William Lubbers, 43.
Hayden began his military career as an active-duty soldier from 1980 to 1988. He did two stints in the Oklahoma National Guard in the 1990s before signing up again for the Army Reserve in December 2003, according to Army records. He served in Iraq until March 2005 and was deployed to Afghanistan in 2009 until the following September.