Tuesday, July 15, 2008
Fact-Check Follies
Dave Farber published a link to factcheck.org on his IP list. Looks like a lot of good stuff there on political lies, etc., but the one fascinating "fact" article that got my attention said that trains can move 438 tons one mile on a gallon of fuel. I dug into it, and it came up short. Factcheck documented the 438 ton-miles per gallon claim nicely. So hey, it's a fact.
But then they try to frame this fact in the context of railroads versus trucks, and they completely fail to answer the question, "How many ton-miles per gallon for a truck?" They quote trucking association executives, "fair and balanced" news-story style, but never address the basic question.
So I did a little Googling and some back-of-the-envelope . . . the max legal gross weight of a truck in the US is 40 tons. The consensus of several sources is that an 18-wheeler gets six miles per gallon on a good day with a following wind (though the average seems to be more like four). So, assuming
1) All of that 40 tons is cargo,
2) trucks are always loaded to the max and never deadhead,
3) trucks get 6 mpg average,
then trucks move 240 tons on a gallon of fuel.
In other words, even when truck efficiency assumptions are absurdly optimistic, trucks only get about half the cargo moving efficiency of rail.
Some more realistic assumptions:
1) 30 tons of cargo to max gross (subtracting empty weight of truck)
2) with light loads, deadheading, et cetera, average load is 75% of max gross
3) 4 MPG
then more realistically, trucks move 90 tons one mile on a gallon of gas diesel.
OK, so the "fact" behind the original factcheck article is that trains are something like five times more efficient than trucks. Factcheck missed this altogether. I wonder how they *really* do on the candidates?
But then they try to frame this fact in the context of railroads versus trucks, and they completely fail to answer the question, "How many ton-miles per gallon for a truck?" They quote trucking association executives, "fair and balanced" news-story style, but never address the basic question.
So I did a little Googling and some back-of-the-envelope . . . the max legal gross weight of a truck in the US is 40 tons. The consensus of several sources is that an 18-wheeler gets six miles per gallon on a good day with a following wind (though the average seems to be more like four). So, assuming
1) All of that 40 tons is cargo,
2) trucks are always loaded to the max and never deadhead,
3) trucks get 6 mpg average,
then trucks move 240 tons on a gallon of fuel.
In other words, even when truck efficiency assumptions are absurdly optimistic, trucks only get about half the cargo moving efficiency of rail.
Some more realistic assumptions:
1) 30 tons of cargo to max gross (subtracting empty weight of truck)
2) with light loads, deadheading, et cetera, average load is 75% of max gross
3) 4 MPG
then more realistically, trucks move 90 tons one mile on a gallon of gas diesel.
OK, so the "fact" behind the original factcheck article is that trains are something like five times more efficient than trucks. Factcheck missed this altogether. I wonder how they *really* do on the candidates?
Technorati Tags: DaveFarber, Framing, Press
Comments:
A back of the envelope for a modern diesel is about 70 kJ/km/metric ton. Diesel has about 45 MJ/gallon, so this is about 640 metric tons (close enough to english tons) per km on a gallon of diesel.
This is at speed (nominally 120 km/hr). Trains have very little rolling resistance and the frontal area is minimal. Power requirements above 70 or 80 km/hr are dominated by a frontal area * Cd * v^3. Frontal area *Cd is pretty low on a train given the amount of stuff they haul.
Acceleration is another issue - you burn LOTS of fuel in that phase.
This is at speed (nominally 120 km/hr). Trains have very little rolling resistance and the frontal area is minimal. Power requirements above 70 or 80 km/hr are dominated by a frontal area * Cd * v^3. Frontal area *Cd is pretty low on a train given the amount of stuff they haul.
Acceleration is another issue - you burn LOTS of fuel in that phase.
I have a hunch that the artificially high price of fuel is engineered in collaboration with middle eastern states to choke China's economic growth or at least slow it down.
It also creates a ton of profits for the oil producers which they would supposedly use to diversify their energy business (think ethanol, liquid coal, etc) like Philip Morris did to diversify its products beyond cigarettes.
Well... that's one theory.
Have you heard of econol?
It also creates a ton of profits for the oil producers which they would supposedly use to diversify their energy business (think ethanol, liquid coal, etc) like Philip Morris did to diversify its products beyond cigarettes.
Well... that's one theory.
Have you heard of econol?
There is one important additional detail that you failed to consider in your train vs truck comparison: trains are fuel-flexible. As far as I know, all long-distance trains in the U.S. are diesel-generator/electric-traction systems (this allows the diesel to run at optimum RPMs and probably allows for better low-speed torque). I believe all "bullet trains" are electric and there is nothing to prevent the US transportation industry from permanently weaning from petroleum. In addition, if it were to prove impractical to electrify all lines, I have no doubt that existing trains could be converted to run on hydrogen (liquid or gaseous). Hydrogen is an extremely weight-efficient fuel (which is why it is usually touted for hypersonic aircraft). Unfortunately, it is not as VOLUME efficient as hydrocarbon fuels. Obviously, such a penalty (approximately 2:1 I believe) would not be a problem for trains. I'm still waiting for hydrogen stations to become available in Phoenix so that I can convert one of my vehicles (legally) to run on hydrogen.
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