When a car travels down a road, it is a particle. But I have this idea that when the traffic on the road becomes dense enough, it begins to behave as a fluid, a compressible fluid. My idea is that we can observe pressure waves moving through the traffic. If a slow down occurs at any point, it is like slamming shut a well. A pressure wave moves out from it causing slows down further back in the traffic long after the original cause of the slow down is gone.

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You're not the first. I think this is an emerging view: emergent phenomena.

This individual has a bunch of pages about it: Science Hobbyist.

Physorg: Traffic jam mystery solved by mathematicians

New Scientist: Shockwave traffic jam recreated for first time

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Nope, not new at all. We used traffic as an example of nonlinear wave effects in my math methods class

There have been several articles published in Physical Review and Physical Review Letters using physics principles to try and understand traffic flow. Go to the PRL website and do a search on "traffic" and "car" and you'll pull up a whole bunch. One of the more interesting ones is Gas-Kinetic-Based Traffic Model Explaining Observed Hysteretic Phase Transition (PRL 81 3402-3404) from 1998. This model looks at phase transitions in traffic flow as a function of density and speed. Quite cool IMO.

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"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind." - William Thompson, 1st Baron Lord Kelvin

"If it was so, it might be, and if it were so, it would be, but as it isn't, it ain't. That's logic!" - Tweedledee

This isn't right. This isn't even wrong. - Wolfgang Pauli

In addition to the comments of others, I want to point out that this is not what is usually meant by "Wave-particle duality". All fluids that we normally deal with are actually made up of particles--atoms and molecules. The wave/particle duality of objects like the photon are a completely different animal (or plant, I'm not sure).

Right-- in particular, wave/particle duality allows the wave formulation to explain the motion of single particles in the absence other particles. That obviously would not apply to traffic.

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Physics doesn't predict the future, it predicts the past that hasn't happened yet.

There are two kinds of delusions, the obvious kind that clearly don't work, and the insidious kind that clearly do.

I've also thought about this problem many times, mostly while sitting in traffic. I've even tried to do something about it, by leaving a little extra space and modulating my acceleration and braking so I don't have to come to a stop even though the cars in front of me do. Not usually very successful as the extra space generally just inspires someone to cut in, causing me to jam the brakes!

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Cum catapultae proscribeantur tum soli proscripti catapultas habeant.

Which is why I try to limit lane changes when I am in heavy traffic. As long as I moving generally with the flow, I see no reason to cheat for a few seconds gained immediately and several minutes lost when traffic jams up.

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Keeper of the Jabberwock

If traffic truly had wave/particle duality, that could be useful. Say you didn't know if you should turn left or right. Just do both! When some of you figures out you reached the intended destination, collapse the waveform and all of you is now there.

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

And the catch-22 is that it is frequent lane changing that causes many slow downs in the first place.

Learning to drive in Los Angeles, I quickly became familiar with the concept of traffic waves. And it was quite interesting to discern that they move in the opposite direction as the cars are moving.