Washington DC's terrible Metro accident -- yikes, I used to ride the red line every day -- made we want to go look up information about the city's train system. So I went to the National Transit Database historical tables to see what I could find. Had there been big changes in services? A drop off in funding? Not really. Here are the total operating expenses of the Metro over the past ten years, in millions and billions of dollars:
 

Of course, this needs to be adjusted for population growth, increased usage and expansion. So here's the growth in total services provided (in billions of miles traveled):

 I combined the two to get the dollars spent per mile traveled. That's increased too: