Passengers board and leave an A Line train at Central Park station in Denver on Monday, March 26, 2018.

(Nathaniel Minor/CPR News)

Colorado's two U.S. senators and two of its seven U.S. House members have urged the Regional Transportation District, RTD's contractor Denver Transit Partners and the Federal Railroad Administration to work together to avoid a potential shut down of the popular A Line to Denver International Airport.

"We cannot afford any further delays or loss of service," wrote Sens. Cory Gardner and Michael Bennet, and U.S. Reps. Diana DeGette and Ed Perlmutter in a letter released Thursday.

The FRA told RTD in November that there are still grave issues with the crossing gates on the A Line and the yet-to-be-opened G Line to Arvada and Wheat Ridge. It gave RTD until the end of this week to present a plan to get the gates fixed within a year, and denied RTD's request to open the G Line.

The delegation wrote that the trains' success is "critical" to their constituents.

"We are encouraged all parties continue to cooperate, but efforts to resolve the grade crossing issues have so far proved insufficient. The action plan is a crucial step toward resolving these issues once and for all," they wrote, adding that they would help facilitate in any way possible.

RTD has said the action plan will be sent in Saturday. They agree with the FRA that the gates need to be fixed, while the contractor, Denver Transit Partners, says the gates are working as designed. 

“Denver Transit Partners has shared with the FRA our position that there appears to be a misapplication of their regulations or a misunderstanding between the FRA and system designers,” said Denver Transit Partners’ chief John Thompson last month.