https://en.wikipedia.org/wiki/A_Line_(RTD)
http://www.thedenverchannel.com/lifestyle/discover-colorado/secrets-of-colorado/secrets-of-colorado-11-secrets-of-the-denver-international-airport-rtd-train-station
https://en.wikipedia.org/wiki/Regional_Transportation_District#Central_Corridor
https://en.wikipedia.org/wiki/Littleton%E2%80%93Mineral_station