There is a whole branch of mathematics devoted to this, though I managed to avoid ever having to learn any of it in detail. But in the end it comes down to the drivers. Each driver on the road will either increase or decrease the damping factor on the native instability that comes with too high volume. If everyone would leave room to always slow down a little slower than the guy in front of them and then speed up a little slower that he does, things will keep flowing. If people over-brake and over-accelerate, instability increases and traffic will end up at a full stop more often.