That is the maximum number of cars that can pass a given point in 2 seconds; it does not mean that a road operating at peak capacity can reach that number.
You also have to take into account cars merging onto the road you are on. Imagine a road acting at peak efficiency, with a car passing every 2 seconds. Now merge in more cars. They are going to push back every car behind by that same 2 seconds.
You can read the section on 'merging' in the link above to read more details.
You also have to take into account cars merging onto the road you are on. Imagine a road acting at peak efficiency, with a car passing every 2 seconds. Now merge in more cars. They are going to push back every car behind by that same 2 seconds.
You can read the section on 'merging' in the link above to read more details.