By Matthew Waller

SAN ANGELO, Texas (Reuters) - Attorneys representing one of the U.S. military veterans injured last week when a freight train collided with a parade float in West Texas said on Monday they are preparing to file a lawsuit, probably against Union Pacific, the operator of the train.

Lawyers Kevin Glasheen and Bob Pottroff said they are representing the family of 31-year-old Army Sergeant Richard Sanchez, one of 16 people injured in the crash on Thursday at the parade in Midland, Texas that was part of planned events saluting U.S. veterans of the Iraq and Afghanistan wars.

Four veterans died in the crash.

Pottroff said he wants to challenge the National Transportation Safety Board's assertion that the train signal system had "functioned as designed" and that no anomalies were found with lights, bells or gates.

The signals gave 20 seconds of warning as required by federal law, the NTSB said. But Pottroff said the signals may have required additional time because of the crossing's design.

"If someone finally gets to the bottom of this, the signal should have given 30-plus seconds," Pottroff told Reuters.

With those extra 10 seconds, the arms of the crossing guard might have fallen in front of the float and saved lives, he said.

He said a lawsuit could be filed as early as Tuesday, likely targeting Union Pacific and possibly Midland-based Smith Industrial, the company that NTSB identified as having provided the flatbed trailer used as a parade float.

Union Pacific spokesman Tom Lange said the company is cooperating with the NTSB and federal, state and local officials to preserve evidence. Lange said the timing of warning signals vary depending on the design of the crossing but are always set within federal requirements.

"The timeline released by the NTSB confirms we met that requirement," he said in an email to Reuters. Continued...