No Subject

 1) Conservative law: The number of cars on the road is conserved.
 2) No car-car collision: There exists characteristic safety 
    distance between cars.

Point 1) reminds people with good background in Physics & 
Engineering about famous continuity equation. 
In my opinion, simple problems are ideal place where you can 
exercise or verify your knowledges for deeper understanding
theory what you learned at Schools. Life is too boring if there 
are only some poor applications (& "over exploited") in the 
Univ. Text-Books !! :-)
 
Back to the problem, the idea is good but the model is primitive. 
I suppose that he did not know how to implement point 2) properly.  
If he could implement point 2) better, it will make the model 
become more realistic.  If he knew at least which parameters in 
reality are important (eg. driver's time reaction, technical data 
such like: car's ac/deceleration, etc.), then his model could have 
more market value :-)  
 I hope that some of you will improve this model or develope 
new one.  Use a chance to learn freely news from others.   
It's boring game that I post a simple problem first and a day after 
Mrs Iga will post a simplest solution :-))

Cheers,
SN  
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On Tue, 26 Oct 1999, Aiviet Nguyen wrote:

> Tu+` model 2 tro+? ddi ba`i toa'n thu+.c cha^'t la` 
> set speed limit cho DMV.
> 
> Model 1 (For VHL) Speed limit la` 55 mile/h.
>    Solution: cha.y vo+'i va^.n to^'c 55miles/h. Lo+`i
> gia?i kho^ng phu. thuo^.c va`o model va` ra^'t
> realistic.
> 
> Model 2 ( Elementary problem for 8th grade)
>      Model high way gio^'ng nhu+ mo^.t ca'i o^'ng
> mo^.t dda^`u va`o va` mo^.t dda^`u ra. Ca^u ho?i ta
> co' the^? cho dda^`u va`o vo+'i rate nhu+ the^' na`o
> dde^? so^' lu+o+.ng dda^`u ra tre^n ddo+n vi. tho+`i
> gian la` max.
> Simplification: kho^ng co`n  mo^.t dda^`u na`o kha'c
> tre^n o^'ng. Gia? thie^'t kho^ng co' hie^.u u+'ng skin
> (va^.n to^'c o+? ca'c la`n kha'c nhau la` nhu+ nhau
> va` kho^ng co' ddo^?i lane...stb....). Ca'c
> simplication kha'c thi` student co' the^? gia? ddi.nh
> the^m mie^~n la` gia?i ddu+o+.c
> 
>    Solution:
>             Lu+u lu+o+.ng  va`o  \rho v  ( v la` va^.n
> to^'c  cu?a  ca'c xe , \rho la` ma^.t ddo^. xe trong
> o^'ng =N/l ). Lu+u lu+o+ng ra to^'i dda ba(`ng lu+u
> lu+o+ng va`o va` ta chi? ca^`n ddo`i ho?i kho^ng co'
> collision. Quy ta('c  na`y co' the^? la^'y tu+` thumb
> rules: dde^? an toa`n ca^`n khoa?ng ca'ch mo^.t tha^n
> xe cho va^.n to^'c 10 miles/h.  Tu+'c la` cha.y vo+'i
> va^.n to^'c v ta ca^`n (v/10 +1) X h cho mo^~i xe ( h
> la` chie^`u da`i cu?a xe). Ma^.t ddo^.  la` nghi.ch
> dda?o cu?a dda.i lu+o+.ng na`y
>          Va^.y lu+u lu+o+.ng va`o dde^? kho^ng co'
> collision ( = LLl ra) la`
> v/ h(v/10+1). Lu+o+.ng na`y dda.t to^'i dda thi` pha/i
> ho?i ho.c sinh lo+'p 10 :-))
> 
> Model 3: Should be more difficult with a lot of exit
> and entrance. It should be model as nested queues.....
> (need further realistic formulation)