Rob Goodspeed posts several charts regarding Metro ridership here in the Washington DC area. This one illustrates the growth in ridership at the relatively new Green Line stations around where I live. The steady growth is impressive and tends to illustrate the point that if you build it, they will come; especially if you build it properly, which is what's happened here. The way Columbia Heights' ridership started out slightly lower than Petworth's but is now rocketing ahead also shows the virtues of allowing intensive development, something I'd like too see even more of in that area where right now it's basically restricted (by law, not by lack of demand) to 14th Street.
Matthew Yglesias is a former writer and editor at The Atlantic.