Right. It doesn't work yet in Denver because it's way too spread out. I agree. I don't agree however that NYC transit only works in the core metro area. The whole time I lived in Brooklyn ('97-'05) I could get anywhere i wanted without a car. By walking into either Penn Station or Grand Central I have my pick of any northeast city including Montreal and Toronto. Millions of people commute using those means trains every day. Density is good. It works. And, it's efficient.