I have experience the stop & go traffic you speak of...and am also baffled by it.
DR der Brucer offered the name of a scientific theory last night that I've not heard of: String Instability ["the Accordion Effect"].
IN WORDS:
Lines of cars on a freeway behave very much like a string, loosely strung with beads, in motion. In ideal conditions, all the cars are equally spaced along the freeway string, the whole strand moving along at 60 MPH. If the lead car has cause to decelerate, or God forbid, stop, even for an instant, the entire string starts to collapse into a solid stretch of bumper-to-bumper cars. Long after the initial car resumes speed, cars at the tail end of the string are still piling up. Every car in the collapsed string adds an additional element of time to how long it will takes the entire string to regain speed again. So, even if the lead car is stopped for only 10 seconds, the 60th car in the string may have quite a few minutes before it has its chance to rejoin the forward motion - and note, all the while more and more cars are being added to the non-moving queue. If you are the 40th car in the queue, the reason for the initial slowdown may not be apparent by the time you reach the point of the initial stoppage. (In many cases, the cause is a driver being cut off by a lane changer or a cell-phone talker making a careless freeway entrance.) At times of heavy freeway traffic, succeeding string collapses often occur before the initial collapse has recovered, resulting in a series of stop and go stretches for no apparent reason. We've all experienced the tunnel effect caused when a three-lane road opens up to four lanes - long lines of bumper to bumper traffic in the three lane segment, and instant clear sailing when we hit the four lane portion. If we had a magical way of having all 50 cars in a string brake at the same time, and at the same rate - and then resume speed at the same time and the same rate, our traffic would behave more like a rod than a string and we could move many more cars per hour - and that "magical way", centralized computer control, is just a few years away for major expressways.
I'm sure David Krumholtz could explain it better, and with neat graphics
der Brucer
