The Bullet and the Foot, Nov 18, 2009

Quote of the Day
A horse!  A horse!  My kingdom for a horse!
		-- Wm. Shakespeare, "Henry VI"
Zen and the art of aggressive driving, Chapter 3: Reading the road
So, now that I've bored you with the math, here is the simple rule: small changes are cheaper than big changes. So the principle that we'll use from here on out is that we like to change our speed as little as possible, and act like someone charges us a quarter to press the brake pedal.

So how do you know what the natural speed of a road is? Especially as it's ever changing?!? Well, trial, error, and observation. Picking the right experience to call on requires knowing the situation you are in. For the balance of this article I will analyze situations one at a time, and give you a glimpse into the dynamics and strategies.

The Slinky
What slows all 'ya down, puts your face in a frown, and causes your car to stall? What's hard on your brakes, and makes your head bakes, it's Slinky, it's Slinky...

Here's the situation. You are driving at speed on the highway. Suddenly in front of you, all traffic comes to a halt. For the next 10 miles traffic starts, gets up to speed, and then comes to a screeching halt again. By the third loop you find yourself not moving for a very long time. You start to appreciate funny bumper stickers on the car in front of you. And, as quickly as it arrived it passes, and you are back to highway speed. No accident. No construction. Just the dreaded slinky.

The slinky is caused by the flow on the highway exceeding the carrying capacity of the highway. It's a similar phenomenon to turning a milk jug directly over. A big splurt shoots out, and then stops. A bubble gets in, and the flow starts, and then it stops. Glug Glug Glug. For milk to flow out, air must flow in.

Grab another full milk jug. (Oh sure, I always have two in the fridge...) Now, turn it halfway over. Notice how the milk just pours out. In fact, milk pouring out of the half turned jug is faster than the overturned jug.

This "half-turned" principle is how you defeat the slinky. The first step when you see traffic coming to a stop ahead of you is to not race there. Start slowing down, first by simply letting go of the throttle.

Pro tip: you should never have your foot on the gas with brake lights in front of you.

As you approach the stopped traffic, begin braking early. This gives that yahoo on your bumper ample warning that something is coming up. Your goal is to slow down enough that traffic starts moving by the time you get to where it's stopped, and thus avoid coming to a complete halt yourself.

The key to remember is that traffic is always "moving", even if the individual cars are not. It's "moving" at an average speed. Find that speed, and never exceed it.

My trick is to accelerate slowly. First to 5mph. Then to 10mph. Possibly to 15mph. I cease adding speed when I see that traffic is slowing down ahead. I maintain my speed until I'm on the bumper of the car in front. I pat myself on the back when I arrive behind the car ahead of me, just as he or she has started to accelerate again.

I find that when people see what I'm up to, they generally start to emulate me. Certainly, there will be that jerk that changes lanes to fill "the void". But they stop doing that when they see that traffic ahead of you isn't really moving.

Never allow a gap of more than a quarter mile to form though. At that point you are impeding the flow of traffic. It's okay to have to do a little accelerating and braking, even as a zen warrior driver. Your role is to round out the spikes, not eliminate them.

I find, and you may feel free to call me a little nuts, that my anti-slinky technique actually alleviates jams ahead of me. And there are some theoretical fluid flow equations that back me up on that. (No pun intended.) The "vacuum" in traffic flow is caused by all of the cars trying to pile onto the same piece of asphalt. My allowing traffic ahead to "breathe" we prevent the vacuum from forming.

And, as we all know, vacuums suck.

That's all the time we have for now boys and girls. Next time we'll discuss, the traffic lights of doom. Until then, have a great day!

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