"speeding increases pollution"?

[CosmicCowboy]

So says the billboard on I-10 coming into downtown from the north. My truck gets the same gas mileage at 75 as it does at 65. Any of you Internet Einsteins want to explain to me how I'm polluting more driving 75?

[Wild Cobra]

So says the billboard on I-10 coming into downtown from the north. My truck gets the same gas mileage at 75 as it does at 65. Any of you Internet Einsteins want to explain to me how I'm polluting more driving 75?

In reality, the power required to propel vehicle through the air is a cube factor.

If it takes 150 HP to go 65 MPH, then it takes 230 HP to go 75 MPH.

I used to think it was a square factor, but I later learned otherwise. Now if it is a square factor, then the 150 HP at 65 MPH would be 200 HP at 75 MPH.

Without extensive and careful monitoring, it's hard to say your mileage is the same.

The sign is silly anyway since modern vehicle exhaust is generally cleaner than the air they take in. Unless... they are counting CO2 as a pollutant... Then it's laughably stupid.

[CosmicCowboy]

My on board computer calculates speed, RPM, fuel passed through the injectors, etc. to calculate and display mileage down to .01. It's basically the same at 75 as it is at 65.

[Wild Cobra]

My on board computer calculates speed, RPM, fuel passed through the injectors, etc. to calculate and display mileage down to .01. It's basically the same at 75 as it is at 65.

That's not the reality of physics though. If you are really getting the same mileage, then maybe there is some built in inhibitor from getting higher mileage? There should be a noticeable difference, especially with a real time onboard computer calculation.

[boutons_deux]

So says the billboard on I-10 coming into downtown from the north. My truck gets the same gas mileage at 75 as it does at 65. Any of you Internet Einsteins want to explain to me how I'm polluting more driving 75?

your personal anecdote nullifies science, just like a Bible humper

wind resistance at 75 is non-linearly more than at 65, so more fuel burned

Speed Kills MPG

How much?

According to studies backed by the department of energy, the average car will be at its advertised MPG at 55 mph. But as the speed increases:

- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph

See the graph below (from fueleconomy.gov):


http://www.mpgforspeed.com/


"At approximately 12 km/h rolling and air resistance have equivalent magnitude. At higher velocities air resistance dominates quite strongly."

http://www.sheldonbrown.com/rinard/aero/formulas.htm

[101A]

That's not the reality of physics though. If you are really getting the same mileage, then maybe there is some built in inhibitor from getting higher mileage? There should be a noticeable difference, especially with a real time onboard computer calculation.

You're not taking into account engine speed/torque - the gearing of his transmission/final drive ratio.

[101A]

[Spurminator]

I don't know the physics, I just question the logic of trying to appeal to speeders with an environmentalist message.

[boutons_deux]

I don't know the physics, I just question the logic of trying to appeal to speeders with an environmentalist message.

agreed.

if gas were $5+/gal, billboards could make an economic appeal

[JoeChalupa]

I obey the law.

[boutons_deux]

I obey the law.

There's a long stretch on I10 West of SA where the limit is 75. Biggest offenders are pickup trucks doing 85+

[Blake]

There's a long stretch on I10 West of SA where the limit is 75. Biggest offenders are pickup trucks doing 85+

It's also 75 heading southeast towards Corpus/Port A

[CosmicCowboy]

You ers driving 65 are a road hazard.

[DMX7]

So says the billboard on I-10 coming into downtown from the north. My truck gets the same gas mileage at 75 as it does at 65. Any of you Internet Einsteins want to explain to me how I'm polluting more driving 75?

The sign is a waste, but you are not getting the same mileage at 75 as you are at 65 (basic physics says so). Einstein would be laughing at you for saying such a thing.

[CosmicCowboy]

The sign is a waste, but you are not getting the same mileage at 75 as you are at 65 (basic physics says so). Einstein would be laughing at you for saying such a thing.

I'm actually aware of the physics but the difference is pretty insignificant. I just thought the sign was pretty dumb.

[boutons_deux]

wind energy is increased by cube of wind speed

75/65 = 1.15, cubed gives about 50% more wind resistance for 15% more speed

[RandomGuy]

So says the billboard on I-10 coming into downtown from the north. My truck gets the same gas mileage at 75 as it does at 65. Any of you Internet Einsteins want to explain to me how I'm polluting more driving 75?

Your mileage is not the same at 75 as it is at 65. Physically impossible.

If you were to record average MPH at those specific speeds and control for variables like wind, elevation changes, and drafting, you would find they are not the same, W/C touched on the most important parts.

Even setting aside these considerations, engines have to be designed for an "average" speed anyway (optimized for a certain RPM), and the farther you get away from that, the farther you get away from that built-in optimal speed. Most US cars still have that "average" speed as 55 or so. (this particular bit is based on an explanation related to me by my brother in law, who was considering at one time becoming a NASCAR mechanic, and has some professional certifications in such things, he is a bit smarter than I am in some regards, and I trust him to get this bit spot on, if not my exact memory of the conversation)

Hope that helps.

[RandomGuy]

I'm actually aware of the physics but the difference is pretty insignificant. I just thought the sign was pretty dumb.

"Accurate" would be a better word.

You might not like the conclusion, but you can't really argue with the physics.

http://www.physicsclassroom.com/clas...Air-Resistance

Most of the way down is a calculator, see for yourself.

Hold all the other variables equal, and add 15% to speed. You get a total force that is about 50% higher.

[Trainwreck2100]

Your mileage is not the same at 75 as it is at 65. Physically impossible.

If you were to record average MPH at those specific speeds and control for variables like wind, elevation changes, and drafting, you would find they are not the same, W/C touched on the most important parts.

Even setting aside these considerations, engines have to be designed for an "average" speed anyway (optimized for a certain RPM), and the farther you get away from that, the farther you get away from that built-in optimal speed. Most US cars still have that "average" speed as 55 or so. (this particular bit is based on an explanation related to me by my brother in law, who was considering at one time becoming a NASCAR mechanic, and has some professional certifications in such things, he is a bit smarter than I am in some regards, and I trust him to get this bit spot on, if not my exact memory of the conversation)

Hope that helps.

I wouldn't say is physically impossible you'd just have to design an engine that works inefficiently at 65 that it burns as much gas at 75

[DarrinS]

People stuck in rush hour traffic doing 10 mph are "polluting" more. Unless, you drive a hybrid like I do.

[RandomGuy]

I don't know the physics, I just question the logic of trying to appeal to speeders with an environmentalist message.

Probably not overly effective. I would point out that the kinetic energy goes up at a squared rate as well. Less gas mileage, and more dangerous.

I still speed tho. Rather spend less of my life in the car.

[RandomGuy]

I wouldn't say is physically impossible you'd just have to design an engine that works inefficiently at 65 that it burns as much gas at 75

I stand corrected. A non-existent engine designed like that would indeed be more efficient.

[Wild Cobra]

You're not taking into account engine speed/torque - the gearing of his transmission/final drive ratio.

You are correct. The torque curve changes the efficiency as well. The ratios will make a difference.

Still, there should be some noticeable change.

[Wild Cobra]

You ers driving 65 are a road hazard.

Agreed.

Give me 130+ MPH any day!

[Wild Cobra]

People stuck in rush hour traffic doing 10 mph are "polluting" more. Unless, you drive a hybrid like I do.

I challenge that idea.

I contend that hybrids actually pollute more. modern internal combustion engines produce almost no emissions. but that is only after their catalytic converter heats up. With the hybrid turning on and off, the catalyst cooling between usage...