My point was the highways were an indirect effect of cars. Highways were a secondary effect of cars and suburbs were a tertiary effect of cars.
What you say makes sense but I think suburbs would have sprung up over time without highways just because the population was growing and people would be willing to move further away from urban areas as cars became safer and more common.
Google "street car conspiracy". The evidence is that car ownership rates had pretty much leveled off. Everyone who wanted a car had one. Most people were pretty happy with street cars. There was an active campaign from moneyed interests to use government to build highways and rip up street cars.
What you say makes sense but I think suburbs would have sprung up over time without highways just because the population was growing and people would be willing to move further away from urban areas as cars became safer and more common.