Saturday, August 16, 2008

The zipper problem

No, this is not a post about John Edwards or Bill Clinton.

It's about traffic congestion -- specifically about the most efficient way to get cars through a bottleneck created when 3 lanes, say, drop down to two. Cynthia Gorney writes:
Nearly every time I asked one of the traffic people to assume the role of the great vehicle arranger in the sky, remote-controlling each of us bottleneck drivers as if we were so many video-game characters, the reply went as follows:

FIRST, EVERYBODY REMAINS UNRUFFLED, without abrupt changes of lane or speed, as the lane-drop comes into view. Everybody takes three deep, cleansing breaths — all right, the experts didn’t say that, but they meant to — and considers both the imminent needs of everybody else and the system as a smoothly functioning whole.

Then everybody begins to slow, not too much, all in concert. All cars remain in their lanes, using all the real estate. ... People in the narrowing left lanes refrain from shooting ahead, while people in the right through lanes — this is hard to swallow, for those of us inclined toward vigilantism, but crucial — leave big spaces in front of their cars for the merging that is about to commence. We resist the freeze-out-the-sidezoomer urge. We prepare to invite them in.

Finally, at clearly marked or somehow mutually agreed upon places, everybody starts conducting beautiful “zipper merges.” That’s the technical term — one-two, one-two or one-two-three, one-two-three — as indicated by the roadway configuration. The process has now worked at its ideal efficiency/equitability ratio: if all have behaved correctly, the tunnel passage has been both benign and, relatively speaking, quick.
The last thing you want to get into is stop and go -- ah, the home drive from Dubai to Sharjah on the Emirates Highway. Slow down together and leave as little real estate unused as safely possible given your mutual speed. Easier said than done.

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Blogger Leo Americanus said...

I really think the only way we're going to be able to manage our traffic problems is by car "auto-pilot." You can't depend on human drivers to move in extreme proximity and synchronization or to zipper merge, so you have to depend on computers and sensors to do it. In congested areas, cars will have to be on auto-pilot, sensing others and moving like a school of fish.

A number of massive problems will be brought up as to why this can't happen:
-Switching from older to newer cars with the required equipment.
-The programming required for a car that got on miles ago and is in the left lane to migrate to the exit lane.
-The external roadway signals required to slow traffic for conditions or to tell the cars to merge down to two lanes from a planned three.
-Contingency plans and redundancy features.

But... which will be cheaper, figuring out how to fit more cars onto the roadway or building more and more roads and taking up valuable land to accomodate inefficient and unsafe human drivers. Aviation is going to similar concepts to maximize efficiency. Cars must be next unless we come up with a new paradigm.

8:17 AM  
Blogger nzm said...

All drivers should be made to watch Freeway Phobia and Goofy's Freeway Troubles.


I remember seeing these in the 70s on "The Wonderful World of Disney" and parts of those educational cartoons still stick in my memory.

Merge like a zip and merging at the very end of the merging lane onto freeways (once you were at the same speed as the freeway traffic) were 2 of them.

It's a pity that Disney hasn't updated them. There's nothing like kids screaming out to their driver parents that they're doing something wrong because Goofy showed them the right way!

4:39 PM  

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