Two of the Denver area’s newest train lines — the University of Colorado A Line and the B Line to Westminster — will keep running under an extension of the temporary waiver issued by the Federal Railroad Administration (FRA).

It’s the latest in a series of extensions of a waiver first issued more than a year ago. It’s to give the Regional Transpiration District more time to work out issues with the timing of crossing gates on the two commuter-rail routes.

The FRA’s waiver requires flaggers…