Re: game theory etc.

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In V9 #627, Joe Elliott asks me about the Nature article I cite. The article is "Coherent moving staes in highway traffic" by Dirk Helbing of Stuttgart, Germany, and Bernardo A. Huberman of Palo Alto, California (Nature; 396: 738-740 [24/31 December 1998]). The article can be found at www.nature.com. 

The investigators use a multiagent simulation technique which has made possible the study of realistic highway traffic patterns and has allowed theories based on driver behavior to be tested. The model assumes competitive interaction between the players and different desired speeds for cars and lorries (large trucks). The model finds that as vehicles are added to a highway, traffic will gradually tend to move in a coherent state as a solid block, at which point its capacity is maximized. Adding more cars will cause a rapid breakdown of the coherent state and stop-and-go traffic. (This must be why they have highway on-ramp meter signals in LA).

The simulations were tested against real-life data which confirmed the validity of the model.

The paper ends: "Compared with 'American' (symmetric) lane-changing rules, 'European' rules seem to be less efficient: an asymmetric lane usage, where lorries mainly keep in one lane and overtaking is carried out in the other lane(s), motivates car drivers to avoid the lorry lane, so that the effective highway capacity is reduced by up to 25%."

Another Nature paper of related interest is "Why cars in the next lane seem to go faster" (Nature 401; 35 (1999)). The authors argue that one is likely to make faulty conclusions in situations where two lanes are moving at the same speed because one generally spends more time being overtaken, and cars that are overtaken disappear from sight as opposed to those that have passed.

My impression that Americans are good at merging early when lanes merge doesn't resonate with Joe's observations. Well, let me just add that I saw a sign in PA on US 30 east of York (2 lanes in each direction). They actually encouraged people to use both lanes and merge just before the obstruction. I am still somewhat puzzled by this sign.

Sonny
'91 164 S
Baltimore
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