Train wheels are pretty interesting. To keep good performance, wheelsets (axle and 2 wheels) are regularly removed and the wheels are machined on a lathe. This

Train wheels are pretty interesting. To keep good performance, wheelsets (axle and 2 wheels) are regularly removed and the wheels are machined on a lathe. This can also be done while the wheels are on the train. Then every couple of years the wheels are popped off the axle and new wheels are pressed on. The axles last like 70 years. With such care, the rolling resistance is very low, but it takes a bit more power to start moving. Despite that, one strong person can push one rail car, usually starting with use of a pry bar. A locomotive cannot actually move many rail cars from rest. That’s why there is slack between each car, and to start, the locomotive is first reversed to push the rail cars together, then moves forward, pulling a single car until the slack is taken up, which pulls the next one, and so on. That’s also why you see one locomotive pulling so many cars. If a train stops on an incline for some reason, it generally needs to reverse all the way down the incline and start again. The static coefficient comes into play during braking and if the locomotive wheels slip under power. For that, sand is applied to increase friction.