One of the major problems with cars is the terrible lack of density. Per-occupant, a car occupies more space on the roadway than any other form of passenger transport. And as cars get larger, that lack of density gets even worse. There's only so much space on the road, so something has to give.
Throughput is directly proportional to the volume of cars, and SUVs have larger volume. Technically perhaps surface area, but there is a psychological effect to height. I believe people also give taller vehicles more space as a rule.
Throughput in congestion is determined mostly by how quickly drivers react to the opportunity to move and how many points of attrition are in a path. Both of what are impacted by the number of cars and how well they break or accelerate, not by their size.
There's space to claim large car cause attrition, but that's completely dependent of the local properties of the streets.
The footprint of the car matters. When cars get 5% longer, the same number of people in cars takes 5% more roadway, which adds up quickly, because the difference between smoothly-flowing traffic and jammed traffic is a fragile equilibrium dominated by breakpoints. Furthermore, heavier cars accelerate and decelerate slower than lighter cars, which has a compounding effect on decreasing overall throughput.
No, the length you need between cars is variable and depends on the speed of traffic and the time it takes for a car to come to a stop. The longer a car is, the heavier it is (frames do not have negative weight), and the heavier it is, the longer the stopping distance is. Please don't bother commenting further on something you're so belligerently clueless about.
