 With the front Lake-Dan Ryan train unable to move forward, the pressure from behind caused the coupling bar between the first two cars to bend and the coupled ends of those two cars to be pushed in the air.As motor power continued to be applied, the first three cars were pushed further upwards, until they jackknifed and fell off the tracks.The second and third cars fell all the way to the street below, while the first car fell onto a track support structure.