Firefighters responded to the 2-alarm fire near I-10 and 19th Avenue west of downtown Phoenix and found a pile of railroad ties fully engulfed, the Phoenix Fire Department said.
The blaze forced the closure of both directions of I-10 late Wednesday, the Arizona Department of Transportation said.
The agency announced that both directions were reopened just before 2:30 a.m. Thursday.
Images of firefighters working to extinguish the fiery mound were taken by the fire department and FOX10 Phoenix.
Fire officials said the cause of the fire was under investigation.