What? Cars per length? What is this unit of? Some wierd linear density? I'm saying that that 18-lane abominations are built only for no other reason than driving cars. You say that car infrastructure is cheap, especially in rural areas, but you seem to ignore(intentionally or not) most expensive and destructive part of it. Which happens to go through rural areas. Or you can name abomination that is purely within city limits?
And public transit just doesn't need this abomination. Public transit works fine even with one lane per direction. Or track if we are talking about trains.