@grue in addition to density I’d add hostility to walking. Some suburbs could easily hit streetcar or better density by allowing homeowners to do multifamily conversions or adding additional dwellings (and getting rid of those lawns would be an environmental win, too) but the ones designed around long winding roads need more fundamental changes. Around where I live it’s a stark contrast where everything built in the white flight era was designed to be frustrating for anyone but drivers.