The University of Colorado A-Line and B-Line will rely on crossing guards at least a little while longer, Regional Transportation District officials said this week.

The Federal Railroad Administration last week granted RTD an additional 90-day extension on a federal waiver that has allowed the Denver transit system to operate the train line while it works toward a permanent fix for its faulty crossing gate software.

“We are superclose,” said RTD spokesman Nate Currey. “We’ll ask for as many extensions as we need to to get it done through their process.”

The federal waiver — which had already been extended several times — was set to expire July 31, and at one point it looked as though another extension might not be needed. RTD in April said it had fixed the gate glitch, which was causing train crossing gates to open and close at the wrong time, leading private sector partner Denver Transit Partners to hire station flaggers as a safety precaution.

But as the July 31 deadline approached, federal regulators still hadn’t given final approval to the fix — and even if they had, Currey said, the flaggers wouldn’t disappear right away. The Colorado Public Utility Commission, too, would have to sign off.

The crossing gate troubles have also delayed the opening of the 11-mile G-Line between Wheat Ridge and Denver Union Station, which uses the same technology. Testing on the line resumed in June, and RTD officials are still pushing to open the line by the end of this year.

But because of the amount of regulatory hurdles that remain, it may not open until 2018.