Here’s my comments after working on a MOW work train dumping ballast for 3 weeks straight…
A typical ballast car can dump both inside and outside of the rails. The older style cars are manually operated and controlled. Typical dumping speed for these is 1-2 mph. The MOW crew has a long breaker bar type device that opens the doors and controls the amount of flow. And yes if the hoghead or a the MOW crew screws up you can end up dumping too much ballast in one spot. The keep to dumping ballast is too keep a steady speed. Easier said than done.
Now modern unit ballast trains are dumped at 4-5 mph, and are GPS and remotely controlled. When I was working the work train (ca 2005-2008?), one day we dumped a whole unit train (35-40 cars) of ballast from Bellingham, WA to the outskirts of Vancouver, BC at 5 mph. We never stopped moving once we got started. My brakeman and conductor (along with the MOW crew) started on the headend, and when we pulled into the siding to tie up for the day (after 12 hours of dumping ballast), everyone was on the rear end. Per the rules, no one was ‘supposed’ to get on/off moving equipment, but no one on my crew ever walked too much that day and I never stopped. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-undecided.gif)So dumping ballast with GPS is a little faster, and more precise as each car has individual controls that are run by the computer.
Now, in the recent years (ca 2016) I’ve seen and heard of ballast trains dumping at 20-30 mph with no human interaction expect the regular train crew.
Now if you use a regular hopper car, I’ve see shortlines place a tie in front of the trailing truck on each car that is dumping to spread the ballast out. Can a flanger be used? I’m sure it could be, but I’ve never seen one in action with a ballast train. I’ve seen spreaders reworking the side profile of the ROW with fresh ballast, but never inside the gauge line.