Cross-posted from PubliCola. In response to last week’s post about how cars cause significant greenhouse gas emissions in addition to what comes out of the tailpipe, some commenters contended that even so, car-dependency is not a problem because cars can be as energy-efficient per passenger-mile as buses and trains. But that perspective is classic “can’t see the forest for the trees,” because vehicle efficiency is just one piece of the puzzle that leads to an efficient urban transportation system. The sexy graph below tells the story (click it to see an enlarged version): For the U.S. we see that in …