THE VIRGINIAN-PILOT
Copyright (c) 1994, Landmark Communications, Inc.
DATE: Saturday, November 5, 1994 TAG: 9411040029
SECTION: FRONT PAGE: A15 EDITION: FINAL
TYPE: Opinion
SOURCE: George Hebert
LENGTH: Medium: 63 lines
How many times have you been caught in a traffic jam, sometimes with a series of long, infuriating stops, only to find things speeding up gradually after a while and the jam dissolved - with no evidence, as you move on, of any ob-struc-tion?
Well, this kind of thing seems to be so common that the traffic engineers and students of driver behavior are devoting much time and microscopic analysis to the discovery of reasons - and possible solutions. Such studies were, in fact, the subject of an article a few weeks ago in Newsweek. The piece was triggered by a congressional hearing on more high-tech management of traffic and the comments of various experts.
From this we learn that re-engineering the roads themselves may not help much: Adding lanes, for example, may just attract more drivers, and we're back where we started. Also, rearranging routes to give motorists alternates to one chokepoint may just create chokepoints somewhere else.
The nub of the problem, more and more theorists agree, is a wave effect, similar to that which can be created in fluids or in the air. On a roadway, somebody suddenly decides, say in a congested stretch, that he or she is too close to the car ahead and slows a bit. The driver just behind this first decelerator also hits the brakes - a little harder - and so on down the line rearward, until some vehicles are actually forced to stop.
Then the reverse happens. There is a slight speedup by some motorist who sees empty space ahead, followed by a chain reaction behind - until a normal pace is resumed and everybody begins to wonder what happened, with some drivers sputtering over the high-handedness of repair planners or over whatever obstacle, unseen to start with and now strangely vanished, had brought on the slowdown.
There are other traffic crunches wave mechanics can explain. There is the odd one, for instance, in which a motorist speeds up a little to block other cars at a point where two lanes are merging, then brakes and sets off a slowdown ripple to the rear. Michael Cassidy, of the University of California, Berkeley, is cited on this. And a point he makes is that such a piling-up occurs beyond, and not (as might be assumed) on the approach to, the merger spot. Just one of the little tricks of wave behavior.
The wave concept also seems consistent with what happens when cars sometimes jam up at a tunnel entrance, where the sudden change in visibility makes drivers hesitant. This was mentioned recently by Norfolk's William L. Jones, when he called to talk about pieces I had written on the use of headlights in the daytime to let others see you better.
It's not clear exactly how the acceptance of the wave-action idea will lead to remedies, but the Newsweek article was hopeful. And at any rate, I suppose a good explanation of what's happening is a good start.
So the next time I'm stalled in some massive snarl out on a big highway (suspecting that there's no real obstacle in the traffic lanes up ahead), I won't fret. I'll just relax in my immobilized car and understand the heck out of the situation. MEMO: Mr. Hebert is a former editor of The Ledger-Star. ILLUSTRATION: Photo
by CNB