Accuracy of CTA Train Tracker

Early last month, the CTA beta launched Train Tracker on transitchicago.com. Unlike the agency’s popular and exceptionally accurate GPS-driven Bus Tracker, Train Tracker estimates arrival times by doing a little math. It takes in rail-signal information (when trains enter and leave stations) and the average time for a train to travel a stretch of track, then spits out arrivals as far out as 15 minutes. So how trustworthy are those times you see on your smartphone? We studied ten trains on each line to get a rough idea of whether you can take a coffee detour and still make your El to work.