A few of the (ridiculous) rules of the DC metro:
Bikes are not allowed on the trains on weekdays between 7am to 10am, then again from 4pm to 7pm.
Bikes are to only be brought into and out of the metro using elevators. Bikes are not allowed on escalators or stairs.
Bikes are not allowed to enter the middle cars- only on either end. Only two bikes per end of the car allowed.
Bikes are allowed on weekends at all times.
Bikes are not allowed on the trains on some major holidays (ie July 4th).
Folding bikes are allowed on trains, but during rush hour prime time on weekdays, must be folded and placed in a bag.
Dumb ****, ain't it?
I regularly break at least 3 of those rules when I do take the train, by the way.