Car traffic expanded in the U.S. cities from the 1920s onwnwards. Before that, the road system and #infrastructure wasn't fit for this mode of #transportation, not to forget the poor safety standard of cars, etc. Cf. https://blogs.loc.gov/maps/2022/08/paving-the-way-traffic-flow-maps-from-the-1920s/
Both, cars and horse-drawn carriages, had their peak at different times.