Replies

Then you should reconsider your emotions in light of the physics of the situation. The way to maintain maximum traffic flow when there is a restriction is to use all the road surface up to the point of the restriction. This means that the traffic lanes zip together at the last moment with each one letting one from the other lane in ahead of them.

When I worked at the GE Reentry Systems facility in Valley Forge during the 60's, it was a beautiful thing to watch the parking lots empty at the end of a day, because the rocket scientists who worked there understood fluid dynamics. The people you are doing a slow burn about are the smart ones.

I'm not talking about full lanes, I'm talking about jerks who come around the side and push their cars in front of those who have gotten into the open lanes. Enough people do this so that your line almost stops.

You can defend your driving methods but I don't think it excuses driving to the front of the line and nudging others out of the way so you don't have to wait.

Rude. Rude. Rude!!

Exactly. Good post.

Finally - some sanity. Great post.

I notice from your profile you don't live in Atlanta. Please move here. Quickly.

The way to maintain maximum traffic flow when there is a restriction is to use all the road surface up to the point of the restriction.

Absolutely, and something no one seems to understand.

Emergent waves are nothing new to engineers, particularly civil engineers or anyone versed in fluid dynamics. The following article is the most simple I could find in 5 minutes to explain the phenomena. http://www.amasci.com/amateur/traffic/traffic1.html by William Beaty, EE.

BTW: I used to work with GE Reentry Systems while replacing the MMII with the MMIII (Mk-12 RS) at Malmstrom AFB in the late '60s. I remember you boys being from King of Prussia PA. The following is really for others, not you specifically.

Invisible accidents

Have you ever been driving on an interstate highway when traffic suddenly slows to a crawl? You inch along for many minutes while waiting to see the accident which must have caused the jam. At the same time you also curse the "rubberneckers" who are causing the whole problem. But then all the cars ahead of you take off at high speed. The jam is over, but no accident, no police cars, nothing. WHAT THE HECK WAS THAT?!! A traffic jam with no cause? In the rear-view mirror you see all the poor saps behind you still stuck in the jam. But why? If all those people could just speed up at the same time, the whole traffic jam would evaporate. Why don't they ever do that? What caused the mysterious slowdown in the first place?

After experiencing many of these "invisible accidents", I came up with the following explanation. To best understand this, imagine that you look down on traffic from an aerial view point. Pretend you're in a Traffic Reporter's helicopter looking downwards.

figure 1. Cars lining up behind an accident

Above in fig. 1 I've drawn a one-lane road, an accident, and a row of cars stuck behind the wreck. Other cars are approaching from the left and stopping too. Suppose that the "wrecked" car (the red one above) has simply become temporarily stuck. Maybe it spun out on ice. What will happen when the red car moves and unplugs the flow?

figure 2. A wave of 'condensed' traffic creeps backwards

Refer to fig. 2 above. In the top row (fig. 2A) the flow is suddenly unplugged. But not all the cars can move, since most cars are stuck behind drivers who are stopped. Figure 2B shows the traffic a few moments later, and figure 2C shows it a few moments after that. Notice the orange car in 2A, and see how it eventually becomes unjammed in 2D and begins moving. At the same time the red car in 2A approaches the jam and is swallowed up.

A MOVING WAVE OF "JAM"

After the wreck is removed, there seems to be no reason for the traffic jam to persist. Yet it does. The reason for this is sensible: if I am stuck behind a car that is stopped, then I have to stop too, and so does the car behind me. All the cars in the jam are in this situation. Even though the wreck is gone, they remain locked at standstill because if they want to move, they ALL have to move at once. They never do, because each driver is waiting for the car ahead to move. If I am in the traffic jam, I'm not going to move forward because I have no room to do so. I'd bump the car ahead of me. We all think like this, so none of us can move.
When the car in front of me leaves, I still cannot accelerate instantly, so I will remain stopped for a moment. I must delay leaving for a moment. If I started up instantly, I'd stay too close to the car ahead of me, and that would not be safe. Each departing car must delay in the same way, and this causes the jam to "evaporate" starting from the forward downstream end. It evaporates in a wave which begins at the forward end of the jam, (near the wreck). The wave eats into the jam from right to left, yet new cars are piling onto the back end of the jam.

Starting at figure 2A, the cars depart from the jam in sequence. In 2B the wave of "evaporation" has moved away from the wreck site, and in 2C and 2D it is far from the wreck. But notice an interesting thing: even though the CARS THEMSELVES are moving from left to right, the "wave of evaporation" moves in the opposite direction. It moves leftwards as it eats into the traffic jam.

There is a second important thing to notice. While some cars are still jammed, more cars are piling up behind them at the trailing end of the jam. Even after the wreck is removed, more cars are still "condensing" onto the back of the jam. The traffic jam is like a solid object whose front end is evaporating and whose back end is growing like a crystal. Cars move left to right, yet look at the the group of stopped cars. The stoppage is creeping slowly upstream, in the opposite direction to the moving cars. The accident is gone, but a "moving wave" of stopped cars remains behind. It's not a traffic jam, it's a shock wave which propagates through the "automotive material". It's a traffic-clot in the blood vessel. It's a travelling wave of traffic-condensation.

NOT CAUSED BY ACCIDENTS

These sorts of travelling waves are common during heavy traffic conditions. An accident isn't needed to create them, sometimes they are caused by near-misses, by people cutting each other off, by merging lanes at a construction site, or simply by extra cars entering from an on-ramp. In traffic engineering lingo, they can be caused by "incidents" on the highway. A single "rubbernecker" could cause one by momentarily stopping to look at something interesting. Whenever you slow way down in order to merge across a lane to get to your upcoming exit, YOU could create one.

Sometimes the traffic waves have have no real cause at all. They appear because tiny random motions can trigger large results. They are like sand ripples and sand dunes, and they just build up for no clear reason. They are like ocean waves caused by the steady breeze, or like the waves which move along a flapping flag. They just "emerge" spontaneously from the writheing lines of traffic. In the science of Nonlinear Dynamics this is called an EMERGENT PHENOMENON."

How long will the "traffic wave" last after the accident is cleared? Its lifetime depends upon the amount of traffic, and on the number of cars trapped in the jam, but sometimes these things can persist for many hours. When traffic is slight, the jam might shrink rapidly to nothing. But if traffic remains heavy, then there's no reason for the travelling wave to ever dissipate at all. Also, if the conditions are just right (if the "condensation" happens faster than the "evaporation",) then even a tiny wave could grow large and larger. Sort of like dropping a tiny seed crystal into a supersaturated solution. When traffic is heavy and unstable, slight braking by any driver can cause the traffic to freeze into a gigantic crystal. Like Kurt Vonnegut's end of the world story CAT'S CRADLE it's the "Ice Nine" of the highways.

So, next time you are commuting and you approach a stoppage, don't think of it as a stupid f@#$% traffic jam. Think of it as a pressure wave which has approached your car and engulfed it. Think of it as a simple living thing which is composed of cars rather than molecules. Stay hopeful that the Crystalline Amoeba poops your car out soon. Take an aerial viewpoint, and visualize the wave which is moving backwards as you move forwards.

A TIMELINE OF CUTTING-EDGE RESEARCH

1993 - Single-lane simulation produces self-organizing emergent patterns: traffic jams
1998 - Self-organized "synchronous flow" discovered in heavy traffic
1998 - Physicists investigating traffic waves(they call them "the pinch effect.")
1998 - Traffic waves only appear during self-organized "sychronized flow"
2000 - Just one fluctuating vehicle can trigger jams
2004 - 1st accurate simulation of traffic waves: drivers must aggressively accel then brake hard.
2004 - New discovery: cruise control can erase traffic jams

If you signal, I let you over.

If you don't signal, I assume you are in that spot because you are fond of that spot and don't want to leave it.

If you flip me off, I smile hugely and give you a big thumbs-up.

The people you are doing a slow burn about are the smart ones.

I'm sure that's what you tell yourself when your cutting in line, "I'm the smart one." It may be using "fluid dynamics" but it is simply impatient and rude. And what do you save by cutting in front of the line? An hour? A half hour? 5 minutes? 45 seconds?

Sincerely

This is a thread that has helped me understand how others think. I am one that expects other to show common courtesy.

When traffic backs up, and drivers volunteer to merge early into a common lane, what irks me is the one that first pulled into the common lane, then sees another driver staying in the vacated lane and driving to the front.

What one usually witnesses are several drivers pulling out of the common lane and back into the empty lane. I expect most people are thinking "Hey, I was here first! Wait your turn!"

The comparison to fluid dynamics is helpful, except that with fluid, the volume accelerates through the restriction. In our traffic examples, the rubberneck syndrome enters. Watch the cars ahead of you and notice that adjacent to the accident, most drivers take their eyes off of the road and want to have a look at what they had to wait for. Only after the obstruction, and multiple open lanes, do they accelerate.

How do we move a maximum numbers of objects past a given point? By having them move faster.

Imagine yourself above the traffic accident in a hovering chopper. You have a stop watch and count the numbers of cars going past the accident in a given time. Fairly low number. (Maybe 10-12 a minute) Now imagine yourself coming back to the same spot during normal heavy traffic that is moving. Count the same cars, in the same lane, going by the same spot. Your count might be as high as 45-60 cars.

The most efficient ways to move the maximum numbers of cars down a road is to get them up to speed and keep them moving.

That is why we often see slow downs at merge lanes. Merging traffic during heavier volume causes most drivers to hesitate, thus slowing traffic and causing backups (or as I call them pileups)

It would be nice, but I know human behavior is not going to allow it, but if drivers would just concentrate on the choke point at moving forward as best they could (accelerating even before the choke point) and getting the speed up, we could slowly begin to build the rate at which a given number of vehicles get past the choke point.

At my freeway offramp we have developed a laboratory to demonstrate rudeness. Housing development in the area has placed a strain on the exit ramp. The exit lane leads for about a 1/4 mile to a light. The left lane must turn left. The right lane must turn right. Another interesting wrinkle is the offramp winds down hill, around curves with trees on both sides. Driver can not observe what is happening at the light until they are nearly there. Most cars are turning right.

What is occurring is traffic is backing up to the interstate causing drivers to pull off in a queue past the fog line up to a 1/2 mile on the interstate. It is a usual wait of about 10 minutes before one reaches the light and the right turn.

What happens is that some of our more brilliant folks exit past the cars that have pulled to the right going down the left lane and jamming (merging) into a space near the light. The high percentage of drivers that have patiently waited become upset and tend more and more of protecting their space. Then the drivers just proceed to the light and instead of turning left like they should, turn right, right into the other cars. Yes, there is the occasional driver not aware of local conditions and find them selves at the bottom of the ramp needing to turn right, but the offenders in most cases are daily commuters and could I say recidivists (repeat offenders).

I call this a laboratory because it is a daily demonstration of rudeness and selfishness versus courtesy and consideration. I bring this example up because those of you that want to drive down an open lane past other slowed vehicles are not demonstrating courtesy, but in effect saying to others that you are more important and will use every advantage the other drivers have allowed to give you a break.

Folks, we are all in this together, trying to get someplace. When you as an individual driver take the opening and deny the others that were ahead of you, for me it is tantamount to "cutting in line"