Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

[Starving Steve]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

If the drag force is proportional to the square of your speed, then so is the mechanical work done (force * distance) and the amount of fuel used. On the other hand your cost of time is inversely proportional to speed.
cost = alpha*speed^2 + beta/speed
Enter your personal values for alpha and beta and locate the minimum on a chart such as the one below

.[ATTACH=CONFIG]3945[/ATTACH]

Ok, I got your attachment to open. Now what is alpha? Is alpha the cost of a gallon of fuel? And what is beta? Is beta the cost of my time? And X.... I would assume is the speed driven since X was squared in your equation.

Intuitively, I think the shape of your function is correct, but put some values on the axises for a Toyota Echo that gets 40 MPG on the highway driven at 70 MPH with windows up and no passengers or extra weight in the car. This is in fact, what my Toyota Echo delivers on I-5 when I drive to or from BC to central Calif. I do not have an air-conditioner in my car, and it is a 5-speed manual transmission..... Yes, eco-frauds and metric nuts in B.C, that is driven at an average 70 MPH and not 70 KPH!

I think 40 MPG is a relevant speed to graph because the Dept. of Transportation in the U.S. wants the average vehicle sold in the U.S to deliver at least 40 MPG, and soon.

[unlucky]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

Ok, I got your attachment to open. Now what is alpha? Is alpha the cost of a gallon of fuel? And what is beta? Is beta the cost of my time? And X.... I would assume is the speed driven since X was squared in your equation.

Intuitively, I think the shape of your function is correct, but put some values on the axises for a Toyota Echo that gets 40 MPG on the highway driven at 70 MPH with windows up and no passengers or extra weight in the car. This is in fact, what my Toyota Echo delivers on I-5 when I drive to or from BC to central Calif. I do not have an air-conditioner in my car, and it is a 5-speed manual transmission..... Yes, eco-frauds and metric nuts in B.C, that is driven at an average 70 MPH and not 70 KPH!

I think 40 MPG is a relevant speed to graph because the Dept. of Transportation in the U.S. wants the average vehicle sold in the U.S to deliver at least 40 MPG, and soon.

Sorry Steve, I cannot tell what the right values are for alpha and beta. You're right that X is the speed driven.

The only informative thing about this type of analysis is the shape of the curve. To calculate alpha and beta will depend on many things, since as the coefficients appearing in the earlier drag force equation, the amount of energy extracted from dollar amount of fuel and converted to mechanical work, etc etc.

The take-away is: it's hard to calculate the optimal speed to drive your car, but the curve shows that it's not zero and it's not as fast as possible.

BTW: I drive a diesel Toyota Corolla 2006 model. It's a lovely, unassuming car. It has a display which shows your mpg in real time. From experience, the optimal efficiency is achieved at roughly 100 Kmh on a flat straight road. (That's about 60 mph). For other cars, the result will differ. Higher mpg can be achieved at lower speeds, so long as I'm not starting and stopping, but 100 Kmh is a good compromise between speed and effiicieny. In practice, as you might expect, the mpg on the display is very closely correlated with the amount of pressure you put on the gas pedal. With a manual gearbox, put the car in high gear and depress the pedal as little as possible.

[Sharky]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

Fuel efficiency is determined not just by atmospheric drag. Engine/drive-train efficiency is the dominant factor at lower speeds.

Overall efficiency tends to be a U-shaped curve; poor at very low speeds and at very high speeds, with the optimum somewhere in between. Some hybrids, such as the Prius, actually get better mileage in relatively slow city traffic than they do on the highway.

Since trucking companies pay drivers on a per-mile basis, optimizing their fuel costs by limiting maximum speed should reduce their total transportation cost. Yes, individual drivers will earn less. However, as a side-effect, it should also create new jobs, since presumably the total number of miles needed will stay the same, while each driver can cover less of them. Either that, or maybe it's a stealth lay-off.

[GRG55]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

...Since trucking companies pay drivers on a per-mile basis, optimizing their fuel costs by limiting maximum speed should reduce their total transportation cost. Yes, individual drivers will earn less. However, as a side-effect, it should also create new jobs, since presumably the total number of miles needed will stay the same, while each driver can cover less of them. Either that, or maybe it's a stealth lay-off.

This sounds like a variation of the same logic the French used to justify a mandatory 35 hour limit to the work week... :-)

[thriftyandboringinohio]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

...Yes, individual drivers will earn less. However, as a side-effect, it should also create new jobs, since presumably the total number of miles needed will stay the same, while each driver can cover less of them. Either that, or maybe it's a stealth lay-off.

Very astute observation.
Trucking companies sell ton miles; this implies more drivers to provide the same ton-miles per year, each earning less.
Rather than a pay cut, it's job-sharing.

[flintlock]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

Performance art.

I got a good chuckle out of that one too.

[flintlock]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

Interesting, it starts with a news item on economics and end up with a physics debate. ..

Very common on here. Spices things up. Also probably the only place you'll see just about any topic ultimately end up with a rant about Stalin, pot heads, and nukes.

[Sharky]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

This sounds like a variation of the same logic the French used to justify a mandatory 35 hour limit to the work week... :-)

Yep. Wouldn't be surprised to that soon in the US, too.

[GRG55]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

Yep. Wouldn't be surprised to that soon in the US, too.

Hey, why stop at 55 mph or 35 hours?

Using that logic suggests that even more jobs can be created by slowing the trucks down to 40 mph and cutting the work week to 30 hours. Hell, let's go for 30 mph and 25 hours, or 25 mph and ... :-)

[ggirod]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

Drag, shmag! I burned through an entire tank of fuel while stuck in a ditch south-west of Flasher, North Dakota while the car was going at zero miles per hour. I flew into the ditch hitting a snow drift that had blown onto the highway, just past a hill-top. I hit that sucker at about 70 MPH. The car flew around backward and into the ditch. The time was 1AM. The tank was full to the top.

All night I was there in the ditch listening to the car radio. I saw lights in the distance, but I knew better than to try to walk through a blizzard on the prairie to try to go to lights on the horizon.

By 7AM, the tank was almost empty. I had burned through an entire tank of gasoline, with some alcohol added to it to keep the fuel-line from freezing. Finally, at 8AM, a North Dakota highway snow-plow came through and pulled my car out of the ditch. I had about given-up, and the tank was onto fumes. If that plow had not come by, I would have froze-to-death when the engine would have stopped running.

Drag is one small part of the fuel efficiency equation, but I think (RPM/ mile of travel) and speed (time to travel) are much more important in fuel economy than the drag co-efficient.

And the other reason why I have gone over to be a speed advocate (just like an adolescent) is that Nixon's (or was it Gerald Ford's ?) 55 MPH limit on America's highways during the 1970s turned-out to be the biggest racket for traffic fines that I had ever seen--- or at least until I moved to British Columbia and witnessed their horse-and-buggy speed limits.

I noticed in B.C, that for the most part, the eco-frauds support the horse-and-buggy speed limits. They think horse-and-buggy speed limits are better for the environment, and they resent car drivers anyway.... I kid you not, but I have actually seen in Victoria, BC where skate-boarders travel faster down streets than car drivers can legally drive.

Oh, where is Flasher, ND? you might ask. Flasher is south-west of Bismarck, ND--- the state capitol. I was travelling north-east out of Rapid City, South Dakota, and making very good time. The road was completely clear of snow, with totally bare pavement, at least until just beyond that hill-top. It was like a re-play of the disaster with the iceberg from out of the darkness and the Titanic in 1912.

Instead of criticizing well understood and accepted physics to justify your position, how about reviewing the alternative that, instead of 70 mph in a blizzard so severe that you were hesitant to leave your car, you drove 45 or even 35 mph. Odds are, that at 45 you would have swerved, maybe messed your pants, and continued on your way, chastened a bit. At 35 you would have commended yourself for responsible driving when the car went straight onward. Suddenly that 25 or 35 mph DECREASE IN SPEED would have saved you a tank of gas and many hours.

And, Please, don't lecture me on driving in snow, my home gets 200-300 inches of snow a year and I drive quite a bit.

[Sharky]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

Hey, why stop at 55 mph or 35 hours?

Using that logic suggests that even more jobs can be created by slowing the trucks down to 40 mph and cutting the work week to 30 hours. Hell, let's go for 30 mph and 25 hours, or 25 mph and ... :-)

You're starting to sound like a real bureaucrat now! That's just the kind of out of the box thinking the Left loves.

[GRG55]

Re: Hit With $4 Diesel, Companies Impose Speed Controls on Drivers

You're starting to sound like a real bureaucrat now! That's just the kind of out of the box thinking the Left loves.

Hey, I love utopia. We must be close to achieving the much awaited "leisure society", not to mention the "paperless office".

And I can't help but notice that the worse the economy gets the more we seem to want to retreat into fantasy...

Jul 25 2011 8:48 AM EDT 4,953
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