With all due respect - I don't understand this. Why would suburban growth not work with tram / local train lines that could be extended? It worked in London - one of the largest cities in the world which had to plan way ahead of time due to its historically narrow streets. I've lived in suburban London for >7 years, and frankly the only time I really needed to use the car was only to haul grocery home. Almost any other travel (including to work) was always achievable with the tube/bus - some combination of these.

What the ground truth was then isn't recorded in history. There are post-facto interpretations. I would argue if the incentives were laid correctly, there was no reason for suburbanism to necessarily lead to growth in automobile consumption.

The US motor companies had a massive clout. Given a choice back then (and the big roads due to the post-war expansion) it possibly made it easy to convince people that a car was a superior and more personal form of travel (think pre-ubiquitous air-conditioning). That's when you need government to think ahead, especially at the local level.