This ignores that a larger area with similar population density would require much more robust transportation systems than currently exists in, oh, the world. Have a happy mental visualization:
Take every car in America on the road right now. Divide by, say, 100, assuming that most are driving ~ 1 hour, and the new density would make their trips within 6 minutes after such a change, and the transport system fits 10 people into the space of one car.
Now, cram them into New Hampshire. And imagine rush-hour traffic.