Triple Entendre (triple_entendre) wrote,
Triple Entendre

Unfinished rant

I followed that link [about evacuations and traffic modelling] and read the comments. One commenter pointed to this paper (PDF), and I read it and made these notes:

except that the study starts out with that assumption rather than proving it.

"The model does not accurately simulate high-speed traffic and does not take
into account following distance, and the stop-and-start model of car movement
is not accurate when traffic is sparse. The model is best for slow traffic (under
15 mph) with frequent stops."

So, part of their model is _already_ starting from a worst-case scenario. When your freeway traffic is stop-and-go and under 15mph, it's already too late to fix anything!

That paper makes assumptions that you can ignore most of the things that normally affect traffic.
My offhanded judgement is that any sensibility of their answer is due to some combination of regression to the mean, the central limit theorem (particularly where the correlation between measured variables has been overestimated) and various other number theories of "just because".

The cellular automata model is cool, though.

They conclude by listing possible solutions and admitting that their results shed no light on
each one due to uncontrolled variables.

None of the math appears to be necessary to the individual conclusions, nor the overall.

They could just have easily based their conclusions directly on their original assumptions and saved all the trouble!

They totally seem to miss the one *interesting* conclusion we can make from the paper: the most important objective of an evacuation plan is to identify _and correct_ any _actual_ physical bottlenecks conditions in the evacuation routes. (The extreme example of this might be the way we have an officer direct traffic at an intersection when the traffic lights are out.) You could completely re-purpose smaller streets in the immediate vicinity of a bottleneck, like heart surgeons grafting blood vessels around a blockage.

You definitely don't need any fancy math to tell you that Travel Time is going to be proportional to the number of cars divided by average traffic speed.

Ahem, sorry. I'm pretty harsh on highway and traffic engineers, at least in this country, because of all their internalized assumptions and lack of creativity.

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