RTD operates light and commuter rail lines serving more than 50 stations throughout the Denver metro area. The rail network includes nine active lines (A, B, C, E, G, N, R, T, W) connecting Union Station to major destinations including Denver Airport, Westminster, Mineral, RidgeGate Parkway, Wheat Ridge, Eastlake & 124th, Peoria, Alameda, and Jefferson County Government Center-Golden. Service varies by line and schedules are available for each route.

RTD provides standard fares at $2.75 for travel outside the Airport Fare Zone and discount fares at $1.35 for eligible riders. The agency serves as a true transit hub, with Union Station at the junction of multiple rail lines as well as Amtrak and numerous bus lines. RTD's infrastructure includes bus shelters with lighting and security cameras at major stops, bike lockers and bike racks at popular stations, and parking facilities. The RTD NextRide App allows customers to plan trips, purchase fares, track trains in real time, view service alerts, and report security concerns.