I didn't think they were making that analogy. I think they were highlighting the inefficiency of car-centric spaces. I can think of several other ways the author's thought experiment breaks down. For example many vehicles will be moving freight and goods, not just people and I don't know if the author has factored in anything like that. Then you could also say well what about the distance the cars are travelling compared to say how far people are likely to walk in comparison. All that said I still think it's a thought provoking way of highlighting how car-centric spaces just suck.