If a person is standing on top of a boxcar of a moving train and not paying attention, an overhead bridge would probably be the low point of your day.
Fifty (?) years ago, I remember there used to be this “warning” device about 100m before bridges. It consisted of 6-10 hanging wires spaced about 6" apart. Anyone riding on top of a train would hit these wires and had about 5 seconds to lie down on top of the car to avoid the bridge. Was there a name for these gadgets? I can’t recall the last time I saw one. When did they stop putting these things over tracks, and why?
In the distant path prior to the invention of air-brakes, train brakemen had to walk across the top of train cars to manually set the brake system on each car. Very dangerous work no doubt, even if they had tell-tales to warn them of approaching bridges.
One sometimes sees similar devices today for truckers. For examples, at truck stops or other places where there might be something with a low clearance (like the roofs over fueling areas), there will be a device like this. If the driver can hear it scraping on the top of the truck, then the truck won’t fit there.
One even sees this in places like supermarkets, near the door to the back-room warehouse area. This is for the benefit of the stock-persons who drive around the store with forklifts piled high with stuff.
The areas around boat ramps sometimes have similar warning lines for sailboats. Ideally, you do not step the mast until you are in the water. Do everything short of that in a prep area, but do not step your mast due to power line concerns.
Rooftop-mounted hand brakes (in modern usage really only a ‘parking brake’ to hold a stationary car in place) began to be phased out around 1970 or so. Most freight cars built since then are constructed without roofwalks, and there is no particular need for crew to ride the roofs of moving cars anyway, so no more need for telltales.
Some covered hoppers and tank cars still have roof-mounted walks or platforms, but these are really intended just for access to the upper hatches when the cars are spotted for loading or unloading.
Freight cars still carry individual brake wheels, though now they are mounted low on the ends so they can be reached from the ground. This is so individual cars or strings can be set out and not roll away.
A one-panel cartoon by Sergio Aragonés shows a freight train, marked “N de M” on the side of the tender, exiting a tunnel, with sombreros and rifles on top of the cars; the engineer’s face shows his realization of what has happened—there were men in sombreros carrying rifles on those boxcars, and the tunnel was not high enough…¡Carramba!