[mkl]

I'm pretty sure central coordination is not required for at least some significant benefit.

If you drive at the average travel speed steadily instead of filling gaps in front of you as soon as they open, that smooths traffic out for the car behind you as well. Traffic waves of stops and starts can still form back a bit behind you, but it's unlikely to happen immediately behind you. If even a small fraction of drivers drove like this, there would be much less opportunity for spontaneous jams to form.

I saw an impressive video demonstrating this a few years ago, but just spent a few minutes failing to find it. It showed a guy driving at the average speed of the car in front, so that the gap opened and closed as traffic in front slowed down, sped up, stopped, etc. There are articles about doing this, and animations, but what made this a compelling video was where it was filmed: a long straight concave-up road full of cars that was coming down a hill, so you could look out the back and see an long line of cars moving smoothly and not jammed, while in front there was a long line of cars stopping and starting chaotically.