The G Line, also known as the Gold Line during construction, is a Regional Transportation District (RTD) electric commuter rail line between Denver Union Station and Wheat Ridge, Colorado. Long scheduled to open in October 2016, the opening was delayed until mid-2019. The reason specified for the delay was timing issues experienced by the other commuter rail lines in the RTD system, which currently require a Federal Railroad Administration waiver to operate their grade crossings manually, and the wireless crossing system used by those lines.

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.