The more than 20,000 daily passengers who ride the University of Colorado A-Line to the airport and the B-Line to Westminster won’t be stranded by a shutdown of both commuter rail lines this weekend after federal regulators on Wednesday gave the Regional Transportation District a 90-day extension to address deficiencies with crossing arms.

RTD faced a possible suspension of service on both lines Saturday, which the Federal Railroad Administration had set as a deadline for fixing the timing of gates at multiple at-grade crossings along the 23-mile A-Line and 6.2-mile B-Line.

“It’s a great thing — we all think it’s a breakthrough,” Nate Currey, an RTD spokesman, said Wednesday. “It’s a very clear path forward.”

That path includes four action items that must be completed by the end of the 90-day period, which expires at the end of January, Currey said.

According to the Federal Railroad Administration letter, RTD needs to make software and hardware timing upgrades that account more accurately for variables along the routes — like passenger loading and unloading times at various stations and the acceleration and deceleration patterns of the trains under different operators.

RTD said the crossing gates are typically closing too early because the software that guides them is set to be as cautious as possible. FRA regulators granted RTD a waiver at the April debut of the A-Line to run the service despite the problems, with the requirement that the agency staff the crossings with flaggers around the clock.

The new timeline’s effect on the opening of the G-Line, connecting Arvada and Wheat Ridge to Denver Union Station, is not yet clear. RTD has said testing on the G-Line, which uses the same technology as the A-Line and B-Line, won’t resume until the issues with the crossing arms are resolved. They’ve set an opening for the G-Line this fall.

Currey said “if things go quickly, we still have a window to test G and open by the end of the year.” But he acknowledged that if the fixes on the other two lines aren’t done on short order, “2017 is a possibility” as a G-Line opening date.

Marc Willis, a spokesman for the FRA, said Wednesday that RTD will need to “continue verifying that its flaggers are properly trained and are fully performing their duties” as long as they are operating under a waiver. He said RTD will have to provide twice-a-week updates to the FRA on progress and hold face-to-face meetings with the federal agency in Washington, D.C. on a monthly basis.

Currey said RTD is grateful it didn’t have to roll out a bus contingency plan to move passengers while train service was suspended.

“Having to do that would draw resources and distract us from getting the tasks accomplished that are before us,” he said.