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With proper braking. the train departs Summit. One of the jobs of the brakeman riding on top of the cars was to make sure that all the wheels were rolling. If you set up the retainer on an empty car, the brakes could be applied so hard that the wheels won't turn. If this happens you have to turn down the retainer on that car to prevent flat spotting the wheels. It would be another ten years before Chard Walker would be manning the depot at Summit. My brother and I spent the night in the depot in 1971. We didn't get a lot of sleep with the trains going by at regular intervals, but we had fun and can make a claim that few other railfans can.
It may look like easy work riding on the top of a boxcar. But try doing this at night, in winter, when the wind is howling, and the rain is freezing to everything it hits. Thank God for better air brake systems.