Designed by architecture firm SOM (Skidmore, Owings & Merrill), the open-air Train Hall stands as the centerpiece of Union Station's redevelopment from former rail yards into a regional transportation hub. Its dynamic sweep is meant to preserve sight lines to the historic station. Currently serving Amtrak's Zephyr trains, the hall will serve four future commuter rail lines to destinations such as Denver International Airport in 2016 and 2018.