The R Line or Aurora Line/I-225 Rail is a Regional Transportation District (RTD) light rail line that serves stations in Aurora, Denver, Greenwood Village, Centennial and Lone Tree. Opening on February 24, 2017, the line was designated as the “R” line, reflecting the letter R’s in “Aurora” and “Ridgegate”.

The Regional Transportation District, more commonly referred to as RTD, is the regional agency operating public transit services in eight out of the twelve counties in the Denver-Aurora-Boulder Combined Statistical Area in the U.S. state of Colorado. It operates over a 2,342-square-mile (6,070 km2) area, serving 3.08 million people. RTD was organized in 1969 and is governed by a 15-member, publicly elected Board of Directors. Directors are elected to a four-year term and represent a specific district of about 180,000 constituents.