Traffic is backed up on the Union Pacific rail line between Chicago and the west coast after a derailment this morning near the Cedar County town of Clarence. Cory Litty witnessed the accident around 7:30.Litty says around a dozen cars went off the tracks in two different areas.No one was injured in the derailment and the cause is not known. A railroad spokesman says the line handles around 50 trains a day. He says they are trying to re-route the trains until things can be cleaned up.