UP via NTSB On Monday, the National Transportation Safety Board determined that an airbrake failure caused the fatal collision between two Union Pacific trains in Granite Canyon, Wyoming. On Oct. 4, 2018, the collision occurred when the air brakes on an eastbound UP freight train failed while descending a hill. According to the NTSB, an air flow restriction in the brake pipe caused the air brake system to fail, and the end-of-train device failed to respond to an emergency brake command. Kinked end-of-railcar air hose on train involved in the November 23, 2018, incident west of Cheyenne, Wyoming.UP via NTSB The striking train collided with the rear of a standing UP freight train at about 55 mph, causing the lead locomotives of the striking train and railcars of both trains to derail.