I think this isn't true for the US any more, maybe it hasn't been true for decades?
WorldBank seems to have the ubranisation rate at around 80% for the US: https://data.worldbank.org/indicator/SP.URB.TOTL.IN.ZS?locat...
There is a bit of a definitional problem, with people living in suburbs identifying as rural, as do folks in exurbs. I don't think they're considered rural, and they're concentrated enough that well-designed public transit could serve them quite well. A decent public transit system means that families in sub/exurbs can go from 2 cars to 1 car without a major drop in quality of life, but they'd save $5k - $10k per year.