Comment by pas

Traffic is one thing. Low-density sprawl itself is more costly. (More roads to maintain, more poles along roadsides, more distance to drive, more pipes, more wiring, every SFH is a big box with a lot more surface where heat exchange happens (and then folks want to keep it warm/cool), every backyard is one more sad lifeless walled garden to water and mow. It adds up.)

And I'm not saying there are no benefits, nor am I saying that the alternatives are so perfect people just somehow don't see it. (I'm saying let's quantify the costs and let people choose. For example I'd spend a lot more on soundproofing and a lot less on backyards and frown lawns, but mostly there's no such option. [Hence the big push for more permissive zoning/permitting/etc.])