[stackcollision]

The slack action from a mile-long train is one of the most awe-inspiring, bone-jarring manifestations of raw power I have ever experienced. The first time I felt it, it established in my mind the idea that freight trains are forces of nature rather than vehicles.

Passenger trains also experience it (though the gear on these trains are slightly stiffer), but those cars are designed to have a much smoother ride, and they are also much shorter (8-10 cars instead of 80-100+). On a long train, it sounds like thunder coming from the front, and then a split second later the entire world shakes.