"RTD said the three commuter lines represent the nation’s first newly constructed commuter rail lines that uses Positive Train Control, a safety system that is federally mandated for commuter rail and freight rail operations."

This seems to be a critical fact that I don't recall being included in any previous coverage about this situation.  Very critical as it explains why they didn't just scrap the new system and use what's always worked elsewhere.  

The A and B lines are the beta test for a brand new technology the feds mandated.  Whee!