DENVER — A few steps forward, one step back.

Flaggers stepped away from their posts along the A Line - Denver's train from Union Station to the airport - earlier this summer, and RTD began the process of asking the federal government's permission to quiet the train's blaring horns.

The flaggers, however, are manning three A Line crossings once again.

According to RTD, they ran into an issue along the G Line, the A Line's sister train that will connect Denver to Wheat Ridge and Arvada that was supposed to open two years ago. The G Line has been running in a testing phase as the A Line awaits total approve from the Federal Railroad Administration.

A crossing gate at one of the G Line stops came down 5 seconds too late during testing, a spokesperson said. RTD decided to look at three similar crossings along the A-line and do software upgrades to prevent similar problems.

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The FRA, as well as state regulators, originally mandated flaggers at each crossing because the crossing gates didn't go down and come up within the standard time limits. Both agencies have since given their okay for the flaggers to be removed.

These flaggers will be there until crews finish the work and the FRA re-certifies those three crossings.

RTD couldn’t tell us how long that would take, or if the timeline for the G-Line's opening has changed.

Both trains operate with the federally-mandated Positive Train Control system. RTD has said in the past that an issue with the wireless technology meant to help PTC operate is to blame for the timing issues.