Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/26/83; site ihuxm.UUCP Path: utzoo!linus!philabs!cmcl2!floyd!vax135!ariel!houti!hogpc!houxm!ihnp4!ihuxm!gjphw From: gjphw@ihuxm.UUCP Newsgroups: net.physics Subject: Traffic and fluid flow Message-ID: <256@ihuxm.UUCP> Date: Wed, 15-Jun-83 10:14:01 EDT Article-I.D.: ihuxm.256 Posted: Wed Jun 15 10:14:01 1983 Date-Received: Sat, 18-Jun-83 21:01:31 EDT Organization: BTL Naperville, Il. Lines: 31 This note is in response to a query by W. Montgomery about the behavior of traffic during rush hours. The original article was posted on 13 Jun 1983. A very well written book titled "Linear and Nonlinear Waves" by Whitham contains, among others, a nice treatment of highway traffic during heavy traffic periods. Engineers can use these techniques quite successfully to study and predict traffic behavior when they design new higways. The traffic is simply considered to be a fluid and most of the laws of fluid motion can be applied. The areas where the traffic flow seems to slow then speed up again are density waves that propagate through the traffic fluid. The speed on the highway is determined by the separation between automobiles (molecules) and the reaction time of drivers. This density wave may have been established by some simple disturbance along the highway, or even by the traffic slowing down while traveling up a hill (increased resistance). The wave then travels on its own. In very heavy traffic, the wave can propagate backward through the traffic flow at up to 20 miles per hour. This wave eventually dies out due to the imperfections in drivers' responses (dispersion). The book is generally a good introduction to wave phenomena in media. It also appears that automobile drivers practice only short range interactions, and that all of those intelligent people become indistinguishable from a collection of insensate molecules when they are behind a wheel. Perhaps crowd behavior is incapable of displaying any long range interactions. Patrick Wyant *!ihuxm!gjphw Bell Labs (Naperville, IL)