When I moved to Boston, the first lesson I learned was any gap in front of me that can fit a car will soon have one there. I think it is big cities in general not just regions.
It is not big cities per se, it is any road that has surpassed carrying capacity. Obviously, this will be seen more in areas more densely populated with cars relative to road capacity.
If you drive in south or east Asia, you will see what naturally happens when the number of vehicles on the path greatly exceed the capacity of the path traveling at a certain speed. You can basically model it as fluid dynamics at a certain point in places like Mumbai and Bangkok.
