On a recent train watching trip, a long tank car train, a “Rolling Pipeline” was stopped for a few minutes by the dispatcher to allow another train to clear. This gave me a good, “close-up” look at the special couplers, Type F shelf couplers, that are used to connect tank cars.
For the longest time, there was pretty much one standard design for railroad couplers. But as cars changed in design and purpose, couplers changed with them. This was especially true with tank cars. Because of their freight often being highly flammable or otherwise dangerous/hazardous, tank cars needed a special coupler to cut down on hazardous chemical spills. With the old couplers, once a car started bouncing around during a derailment, the couplers often disengaged and sometimes punctured the car ahead or behind them causing a spill and possibly a fire as well. The Type F coupler was designed to cut down on that risk.
Unlike normal Type E couplers, the Type F model is taller and has machining on the inside of the coupler to help maintain their connectivity in the event of a derailment. As mentioned previously, the benefit of this is that the coupler is less likely to disengage in an accident. But as usual, if you solve one problem, you oftentimes create another one. In this case, because the cars are less likely to disengage, they are MORE LIKELY to pull another car off of the track if they do tip over. Fortunately, the cars are structurally sound and this is often the lesser of two evils.
Anyway, the next time you are stopped at a crossing and a tank train is rolling along, take note of the Type F shelf couplers and know that they are there for increased railroad safety.