Fuelly Forums - Traffic flow

zpiloto,

There are at least two factors that "real driving" has compared to the laws of physics: 1) Car Insurance and fear of premium hikes 2) Law Enforcement and fear of getting a ticket.

In the law of physics known as the "Bernoulli's Principle" that states "if the cross-sectional area of flow is reduced, then the speed of the fluid moving through the flow is increased and pressure decreases." It's the fundamental principle of how an airplane wing works to create lift because the air on top of the wing is moving faster than the air below the wing creating a relative lower pressure on top of the wing compared to the relatively higher pressure below the wing. What does aerodynamics have to do with traffic flows? I'll explain.

Let's say you've got a two lane highway, one lane coming and one lane going. Let's assume there's two cars going exactly at 65 mph and separated by enough space between them to not hit each other, yet not enough space for anyone to merge between them. Now, let's say the two lane highway becomes a four lane highway, two lanes coming, and two lanes going. Based on the Bernoulli's Principle, since the number of lanes increased, the speed of the fluid, or in this case two cars, should reduce. So let's say car #1 merges to the left to go to lane #1 and car #2 stays in lane #2. Let's also say they both slow down to 55 mph.

Now, later on, the four lane highway turns back to a two lane highway. So according to Bernoulli's Principle, both cars currently going at 55 mph should speed up to 65 mph. So car #1 in lane #1 accelerates from 55 mph to 65 mph. Car #2 in lane #2 also accelerates from 55 mph to 65 mph. Now car #1 and car #2 are neck and neck. Then, the transition from four lane to two lane occurs. Now, regardless of right of way rules, this is how "real driving" is different from the Bernoulli's Principle in that air molecules belongs to their streamline. However, cars are supposed to stay in lanes. So going back to this situation, since the cars are neck and neck, one car needs to decide to slow down since exceeding the speed limit may "attract" law enforcement. So let's say car #2 decides to slow down to let car #1 maintain 65 mph and lets car #1 merge right from the old lane #1 to the new lane #1. The driver of car #2 from a behavior standpoint decided to slow down not only to be "nice" but to avoid a car accident which would pretty much be guaranteed to be the driver of car #2's fault. The car accident would result in higher car insurance premiums, so it's in the driver of car #2's best interest to avoid the car accident. However, due to car #2 slowing down, bingo, contributes to the slowdown of the traffic flow behind it. So a traffic jam is starting to be formed because in real life, there's hardly only two cars driving on the highways like this example. The overall fear of the penalty of an accident has also created the oxymoronic phrase "fast lane" during "rush hour."

Now, the best thing to maintain an overall same flow rate through lane constrictions, such as four lane highway becoming a two lane highway, in accordance with the Bernoulli's Principle, is to let the cars accelerate and speed up during the traffic constriction section of the highway. Once cleared of the traffic constriction section of the highway, then the cars should reduce speed back down to 65 mph or whatever the speed limit is. However, this is where the behavior of "fear of law enforcement to get a speeding ticket" contradicts Bernoulli's Principle. Sometimes, the traffic flow constrictions are due to: 1) accident cleanup or 2) construction. In the case of construction, not only is there a speed limit, but sometimes there's an even further reduced speed limit during construction zones. That further restriction of speed limit during traffic constriction further contradicts the requirement of the Bernoulli's Principle that the fluid, in this case traffic flow, is required to INCREASE in order to maintain a steady flow before, during, and after the flow restriction. But once again, the penalty of not only obeying the non-construction speed limit is relatively lower than the penalty of not obeying the construction zone reduced speed limit further aggravates the overall violation of Bernoulli's Principle to help maintain an overall smooth traffic flow.

As far as the "problem" of traffic light induced "waves," sounds a bit too simplistic for me. The author is talking about basically driving straight and only straight. Not about waiting at the STOP arrow/light to turn left and if you execute a right turn quickly enough, then his story seems to jive. The problem/solution seems to assume that there's only traffic lights involved and NO stop signs. So theoretically, even with infinite "antitraffic buffer" he's gonna have to come to a complete stop at some point. A complete stop means that at some point, you're gonna stop the traffic flow of those behind you so how do these techniques help them? What if you're the one who's stuck now?

Although I have to agree with some of his points. When I'm stuck in an extreme traffic jam situation, I merge over to the right, then just keep rolling on basic idle power. A lot of space opens up in front of me because the car in front of me was in a rush to get to push the brake pedal again. So I'd see the same behavior of the car in front of "go, then stop, go, then stop." Well, since I'm the one behind the car, it's quite annoying to do go, then stop driving for miles. I'd rather be actually moving for as long a distance as I can before pushing the brake pedal again. Since I prefer that, I'm imagining that all the cars behind me would appreciate my help in reducing their brake system costs like more frequent replacement of brake pads. So I just happily roll along at idle power. Then as the frequency of the go, then stop behavior of the car in front of me goes down, then that's when I nudge the RPMs a little higher than idle power by about 100~200 RPM. In the end, I feel that not only am I conserving my own brake pads but the brake pads of those behind me so I feel good about what I do.

So in summary, the insurance and legal system conflicts with the requirements of the law of physics known as the Bernoulli's Principle in order to achieve and maintain a consistant traffic flow on the highways. Since there's 50 states in the United States, there are 50 ways to earn your driver's license and therefore 50 ways of driver's education that needs to be changed to accomodate the instruction and testing of the knowledge of "traffic waves", "antitraffic", and other terms used in that link.

cfg83,

You asked "I wonder what the Urban Transportation/Planners have to say about this?" Remember that things like Urban Transportation/Planners work for the local government. Remember that local government adds a sales tax on top of federal taxes to gasoline sales. Remember that taxes is the main method of revenues for the local government. So by conserving their budget resources by NOT fixing the highway traffic jam problem, your car's fuel economy goes from highway FE to basically City FE or worse leads to more frequent trips to a gas station and pay the federal and local sales tax on gas. So from a "business decision" basis, by government not spending money to fix the highway traffic jam problem, it increases their tax collection income and makes them happier. It's good to know that there's websites like GasSavers that may be a more effective education program for drivers than expecting the government to start teaching and testing on "antitraffic" and other materials.

I hope I made sense and hoping I helped.