The first 13 miles (21 km) from downtown Denver to 124th Avenue in Thornton opened as part of the FasTracks expansion plan on September 21, 2020.

[1] When fully built out the line will be 18.5 miles (29.8 km) long and pass through Denver, Commerce City, Northglenn, and Thornton.

In the 2004 election year voters approved the North Metro Corridor as part of the RTD FasTracks expansion plan.

In September 2006 the Environmental Impact Statement (EIS) was started, with completion in late 2010, and gaining approval by the Federal Transit Administration in April 2011.

The contract to build the North Metro Rail line to 124th Avenue was awarded to Graham, Balfour Beatty, Hamon Constructors (GBBH) in November 2013 with notice to proceed in December 2013.

From there it passes under Interstate 76 and Colorado State Highway 224, then again over the South Platte River following a slightly northwest path north until the Original Thornton/88th station.