Why are there delays on the M50 when there are no collisions?

Why are there delays on the M50 when there are no collisions?...Probably the question we are asked most on Live Drive. The phenomenon of "phantom slowdowns" or "brakelight backlogs" as we call them are a hard one to explain without demonstrating them so below are a couple of things that might go some way to clarifying why they happen.

First is a video created by MIT which highlights the effect of one vehicle slowing only slightly

The second is a traffic simulator which gives you control over the many factors that affect traffic. It is interesting to see that just the slightest change from the norm can cause massive delays. Be warned though it is kind of hynpnotic and a little bit addictive.

http://www.traffic-simulation.de/

If those aren't enough for you here are a couple of articles which should quench your thirst for knowledge:

http://nautil.us/issue/3/in-transit/traffic-ghost-hunting
http://www.wired.com/autopia/2009/06/phantom-jams/