I have unloaded several hundred carloads of ballast on two different railroads using the tie method. We often unloaded a dozen or more cars per day with a three-man crew. The one danger is if the tie happens to catch a "lipped" joint and the forward momentum of the train derails the car. This usually results in the truck slewing to one side, and in loose stone, it's a b**** to rerail. It's also grim if you have to close up the doors to skip over a switch or a road crossing. We finally started using comalongs, one on each side, to regulate the flow of stone and to allow us to close up the doors as needed.