The evolution of a rail transit system, illustrated

David Alpert of the Greater Greater Washington blog has posted a terrific slide show indicating how DC's Metrorail transit system grew, one segment at a time, over 40 years.  Here are three of the 31 images in the post:

He also has an image showing how service had to be cut back during the current "snowmageddon/snowpocalypse" blizzard, and some images showing how service might be cut back later this year if funding for the system is not found.  He explains how he did it, too.  Go here for the post and slides.