Friday, February 11, 2011

Traffic Is A Gas

Gases are defined by the Ideal Gas Law.

PV = nRT

Decrease the pressure and the volume increases. Add roads to increase volume in an attempt to decreases traffic pressure and you get stymied because your n is not a constant and not predictable. It increases as volume does. So like a gas filling an empty balloon, traffic will fill the roads given to it even though individual drivers are unpredictable. This is why cutting edge university Engineering Departments model traffic as a kinetic gas.

In other words, a gas will find equilibrium across the volume given to it.

Optimization is different. Optimization is constricting volume to force the flow where you want it to go.

How I think about this is like a gas grill.

Your tank connects to the grill, you turn a valve (a stop light?) and the gas is evenly distributed through many tiny holes for an even heat.

This is equilibrium. Equilibrium is gas using all of these jets evenly. It is calm.

But if you need to crank up the heat on your grill for searing then you use a dedicated burner that has an almost direct line to the gas source.

This is optimization. Optimization is forcing the gas to use one area of your grill.

Traffic calming attempts to slow down the flow so that equilibrium is attained.

If you want to optimize traffic you have to force it by closing other roads. This is why the Andrews University study shows a Boardman Lake Boulevard but also closes off Cass. On net the number of roads doesn't really change in their class exercise.

But Cass is not going to be closed. Not just is it the lifeblood of many businesses but this is also the historical route into Traverse City. You've probably seen the "Old Indian Trail" markers around - I was curious about them so I mapped out their route from Lake Mitchell to Grand Traverse Bay.

This route that has been used for hundreds if not thousands of years and it followed the terrain across the Country Club and then right down present day Cass.

View Cadillac to Traverse City Old Indian Trail in a larger map

I mention this only for perspective, I'm not saying "this is how it has always been so let's not change it" but it is worth noting that this path has a certain allure since out of all available paths, it was used.

Change is needed. Traffic through Old Town is coming and going somewhere. But adding a link to the traffic network will only allow the gas that is traffic to expand to fill the new route.

And isn't it traffic volume that the loudest complaints are about?

Has anyone ever been injured by traffic volume though? Couldn't high traffic volume be considered beneficial? The people in those cars are full of potential - potential customers, potential employees, potential friends - better to have too many than not enough. What about traffic speed? I have had plenty of close calls due to speeding traffic in Old Town. Heck, I even find myself and my pedestrian-centric attitude challenged sometimes when I am driving and turn to head north on Lave Ave and see an uninterrupted stretch down to Eighth - I feel a primordial urge to floor the gas pedal.

I believe we need to address the speed problem first.

So what can be done to calm the traffic system for all the neighborhoods? And how to do it in a way that provides better flow and better safety on both sides of the windshield?

First thing is to think about it as a system and not individual street. This is where I think smart designs like roundabouts can play a role.

I was dubious of roundabouts initially. Though the argument that tourists won't understand them doesn't work for me - tourists seem just fine with our city's one-way streets. Plus traffic lights were new in the 1920's yet people quickly got used to them. Same thing with the "Michigan left". People can deal with it.

The planets of the solar system interact with each other and this is how I think about in-town traffic. It is a system where the mass of one body can interact with another. This is why I think of traffic roundabouts like the gas giant planets. Their presence protects the inner system from rogue comets and asteroids but their mass also allows astrophysicists to use them as gravitational slingshots like the Cassini interplanet trajectory

Image from Wikipedia Commons

Similarly the neighborhoods of Traverse City can be protected by roundabouts at the peripheries. Shunting and routing traffic in the proper direction by encouraging its flow without stopping it.

Because the human brain is built to prefer motion over non-motion. Think about Lake Ave - cutting down Twelfth and by Oryana to Lake Ave is actually a longer path and a longer trip than going Cass to Eighth but involves fewer stops so it is perceived as being shorter (also another case of traffic finding an equilibrium).

Roundabouts work in a similar way. Traffic is slowed down but doesn't stop so the overall experience is perceived as being more efficient. Concomitantly this efficiency will lead to roundabouts directing traffic away from the inner neighborhoods. And like the inner planets being protected from cosmic debris by the gas giants, the inner neighborhoods will be friendlier to life with traffic speeding through them.

Next will be part 2 - "You can't undo a road".