As someone who spent many a year commuting on the DC Metro I have to say I'm surprised that you don't hear stories like this more often.

A man who boarded a Metro subway train in Montgomery County on Monday morning was found dead in the same train five hours later, the transit system said.

Metro said in a statement that the death was probably the result of natural causes, but no detailed information on a cause could be learned. It was also unclear when the man might have died during a period in which the train traveled much of the Red Line in both directions.