Burton and Zorine Lindner died when a coal train left the tracks and the bridge it was on collapsed.
Their car was trapped in the debris and it wasn't found until the next day. Memorials have been placed at the scene.
The couple's sons say they worry about the safety of the country's infrastructure.
"In addition to my own concern about what's going on with my family, I have concerns for the wider community," Rob Lindner said. "As the days pass and we've still gotten no information the anger builds on a daily basis for me."
Union Pacific lawyers said at the time of the derailment inspections of the railroad tracks were up to date.