Chicago Transit Authority (CTA) operates mass transit within the City of Chicago, IL and 40 surrounding suburbs. CTA operates both trains and busses. The train service is known as the L-train, which is short for elevated. Each line is referred to by a color: red line, orange line, yellow line, green line, blue line, purple line, brown line, pink line.
Shows the "instant" that the monitor started returning a response (in ms).