>>>Yes, I was thinking of that because I'd heard of it here, too. I always wondered why the coin didn't fall off the rail from the vibrations.
>>
>>Maybe because the vibrations are vertical, and the coin has too good a ratio of surface against height.
>
>Yes, but doesn't the rail have just a bit of a crown on it (to help shed water, I would assume). Seems like that would make the coin more likely to fall off.

Crown? Wouldn't know, we were a republic ;).

There's some curvature near the edges, but very slight. Generally, the trains tend to flatten that, just like they flatten the coins. The wheels actually didn't seem completely cylindrical, though - more slightly conical, but that could have been an illusion. Never really looked at that close up.