The old rail starts to follow rollers that move it up and over to the side, out of the way of the ties and the new rail that will be following similar rollers to move it from the inside under the old rail and into position. At the position where the new and old rails cross over/under each other there are two big Grabber arms that pick up the old tie and put it on a conveyor and then grab a new tie off a different conveyor and place it onto the ballast, (2 foot on Center).