Union Pacific continues to investigate the cause of a Friday morning derailment in Tucson.

A freight train was traveling from Nogales to Tucson when eight empty cars derailed near East 16th Street and South Euclid Avenue, Aaron Hunt, a California-based spokesman for Union Pacific, said in an email.

The incident, which occurred around 6 a.m., closed roads in mid- and downtown Tucson until about noon, causing rush hour drivers to find alternate routes from East 16th Street and South Toole Avenue to East 22nd Street near Santa Rita Park, said Sgt. Chris Widmer, spokesman for the Tucson Police Department.

No one was injured in the incident, said Capt. Barrett Baker, spokesman for the Tucson Fire Department.

No other trains were delayed because of this incident, Hunt said.