RTD is going to operate its own commuter rail line, if and when, the N Line to Thornton opens.

DENVER — The Regional Transportation District (RTD) announced Tuesday that a commuter rail meant to connect Denver, Commerce City, Northglenn and Thornton will not open until "May or August" 2020.

Most recently, RTD has said it hoped to open the N Line (N standing for North Metro) early next year. It was originally supposed to open in 2018.

Once the N Line is done being constructed, RTD plans to operate it itself, and not contract it out to Denver Transit Partners, which currently runs the A Line to Denver International Airport, the B Line to Westminster and the G Line to Wheat Ridge and Arvada.

An announcement about the delay says that RTD General Manager and CEO Dave Genova said, "specific milestones still must be met before an opening date can be determined."

This includes testing grade crossing and positive train control as well as getting the project from the current contractor.

Positive train control is the safety system that RTD and Denver Transit Partners were the first to build into a rail line from the ground up when the A Line opened in 2016. It's also part of what caused timing issues at crossings, forcing flaggers to be posted at the crossings for more than 2 years.

The 18.5-mile commuter rail line is part of FasTracks, RTD’s 2004 voter-approved, multibillion-dollar transit expansion plan for the metro Denver region.