There’s been massive investment in passenger rail lines in Metro Denver over the last 15 years. But these billions of dollars have done little to shift how people move around here. Why is that? It’s one of the questions driving a new podcast from CPR News. “Ghost Train” is out now. It’s about building a greener transportation system in Colorado - both the obstacles and new thinking. It’s the brainchild of CPR transportation reporter Nathaniel Minor, who’s here to share the first episode.