Chicago CTA train
line that connects the northern suburb
s of Evanston, Illinois
and Wilmette, Illinois
to the city (Chicago, Illinois
The line generally runs between the Linden station in Wilmette and the Howard station at the northern edge of Chicago's city limits. Most of its stops are in Evanston. In order to get to the rest of Chicago, a passenger would transfer to the Red Line train at Howard.
However, the Purple Line does run express trains during morning and late afternoon rush hours. These trains have the same stops as above, but instead of ending at Howard, they continue south, going express from Howard to Belmont. They then proceed to mirror the Brown Line from there (by going to The Loop downtown, before returning north).
The express portion is notable, since going from Howard to Belmont would be 13 stops on the Red Line. Therefore when the Purple express is running, it makes the commute from Evanston to downtown quite quick (which leads Evanston residents to wonder why the express doesn't run more often).
The "normal" route (between Linden and Howard) runs daily until the early morning, at which time one can take a bus that runs along the same path for the overnight hours.
Noding note: "Purple Line" seems like a vague title; but it's consistent with the other Chicago CTA nodes (Red Line, Brown Line, Blue Line, Green Line, Orange Line, and Yellow Line).