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> Take a 40t truck with 5 axles vs. a small car with a weight of 1t and two axles ... Truck driver. Not quibbling, just adding nuance. For your typical 40t sc

by a3n 7y ago

> Take a 40t truck with 5 axles vs. a small car with a weight of 1t and two axles ... Truck driver. Not quibbling, just adding nuance. For your typical 40t scenario, allowed max weights are: 12,00 pounds on the front steering axle. It has one tire at each end. 34,000 pounds total on the two tandem "drive" axles on the truck. There are two tires at the end of each axle, so four per axle, eight total at the drive axles, and ten total on the truck. 34,000 pounds on the two tandem axles on the trailer, two tires at the end of each axle, eight total on the trailer axles, 18 total on the truck plus trailer rig. 34K + 34K + 12K = 80,000 pounds = 40t, if the trailer is fully loaded to max. It's about 35,000 pounds total if the trailer is empty. So you should include in your calculations that the load is spread out over eighteen tires, as above. There is also bridge loading to consider. https://en.wikipedia.org/wiki/Federal_Bridge_Gross_Weight_Formula https://en.wikipedia.org/wiki/Federal_Bridge_Gross_Weight_Fo...

dhimes 7y ago
So it would be better to have a bunch of smaller trucks moving cargo. And that means a lot more work for truck drivers.
- a3n 7y ago
  Lots of ways to cut that. Consider pounds-mile/gal for freight on my 80k truck carrying 45k freight, vs your vanagon or beemer. My truck gets at least 6mpg, usually 7.5, sometimes 9, and I've seen 10 once.
- richk449 7y ago
  True, reducing the cargo would require more trucks to carry the same load, increasing demand for truck drivers. On the other hand, wouldn’t reducing the amount of cargo a single truck can carry makey individual truck driver less valuable? The end result would probably depend on a lot of other factors, including the supply and demand curves for alternative forms of transportation (trains, boats, investment in autonomous solutions), as well as the supply and demand curves of the goods being transported (because if the cost goes up to pay for more truck drivers, maybe people will just stop buying that product).
- TheDong 7y ago
  It may be better for the roads, but it may be overall worse for the environment and/or shipping costs. Building an entire truck isn't free from cost and environmental impact, nor is maintaining it. Fuel usage also increases with more trucks. There's also an overhead each truck has that scales differently from how much it lugs, based on fuel it needs to carry and space for its driver.
- cronix 7y ago
  Or for the companies who will own/lease the automated fleets, foregoing having to pay wages, health insurance, vacation time, or work breaks allowing them to ship quicker since they aren't forced to stop driving and take a break every x hours. You'll just get a smug smile and a "learn to code" line.
- xenonite 7y ago
  No, for the roads it would be better to have the weight distributed on more "area", hence: more wheels and bigger wheels for the same weight. And this does _not_ require more trucks, just more wheels below each truck. However, an even more material-efficient solution would be to use railways instead.
masklinn 7y ago
> Truck driver. Not quibbling, just adding nuance. You're absolutely quibbling though. > So you should include in your calculations that the load is spread out over eighteen tires, as above. The fourth power rule is specifically about axle load, not about wheel load. It's also an estimate / rule of thumb (which is why it's so useful), not a precision instrument. But hey if you want more precision than the FPR we can do more precision: https://pavementinteractive.org/reference-desk/design/design-parameters/equivalent-single-axle-load/ https://pavementinteractive.org/reference-desk/design/design... As the link notes, road engineers usually work in LEF/ESAL (ratio to a standardised 18000lbs axle load), and provides some conversion tables. Assuming a relatively large 4000lbs sedan this is 2000 lbs per axle, or 2x0.0003 LEF = 0.0006 LEF. A fully loaded truck would be ~0.3 for the 12000lbs front axle, and 1.11 for each of the rear tandem axles, for a total of 2.52 LEF. 2.52 / 0.0006 = 4200. Which shows that the fourth power rule's 4096 was pretty close but if anything underselling it.
- jessaustin 7y ago
  Yeah, they use dual tires so that they don't pop catastrophically, not to spare the road from wear.
  - reitzensteinm 7y ago
    I'm sure that's true, but are you saying it doesn't reduce wear?
    - masklinn 7y ago
      I'm sure it reduces wear on the tires.
      - reitzensteinm 7y ago
        "The AASHTO load-equivalency factors strictly apply only to axles supported at each end by dual tires. Recent increase in steering-axle loadings and more extensive use of single tires on load-bearing axles have precipitated efforts to examine the effect on pavement wear of substituting single for dual tires." https://www.fhwa.dot.gov/reports/tswstudy/TSWwp3.pdf https://www.fhwa.dot.gov/reports/tswstudy/TSWwp3.pdf

by a3n 7y ago

dhimes 7y ago

So it would be better to have a bunch of smaller trucks moving cargo. And that means a lot more work for truck drivers.

a3n 7y ago
Lots of ways to cut that. Consider pounds-mile/gal for freight on my 80k truck carrying 45k freight, vs your vanagon or beemer. My truck gets at least 6mpg, usually 7.5, sometimes 9, and I've seen 10 once.
richk449 7y ago
True, reducing the cargo would require more trucks to carry the same load, increasing demand for truck drivers. On the other hand, wouldn’t reducing the amount of cargo a single truck can carry makey individual truck driver less valuable? The end result would probably depend on a lot of other factors, including the supply and demand curves for alternative forms of transportation (trains, boats, investment in autonomous solutions), as well as the supply and demand curves of the goods being transported (because if the cost goes up to pay for more truck drivers, maybe people will just stop buying that product).
TheDong 7y ago
It may be better for the roads, but it may be overall worse for the environment and/or shipping costs. Building an entire truck isn't free from cost and environmental impact, nor is maintaining it. Fuel usage also increases with more trucks. There's also an overhead each truck has that scales differently from how much it lugs, based on fuel it needs to carry and space for its driver.
cronix 7y ago
Or for the companies who will own/lease the automated fleets, foregoing having to pay wages, health insurance, vacation time, or work breaks allowing them to ship quicker since they aren't forced to stop driving and take a break every x hours. You'll just get a smug smile and a "learn to code" line.
xenonite 7y ago
No, for the roads it would be better to have the weight distributed on more "area", hence: more wheels and bigger wheels for the same weight. And this does _not_ require more trucks, just more wheels below each truck. However, an even more material-efficient solution would be to use railways instead.

masklinn 7y ago

> Truck driver. Not quibbling, just adding nuance. You're absolutely quibbling though. > So you should include in your calculations that the load is spread out over eighteen tires, as above. The fourth power rule is specifically about axle load, not about wheel load. It's also an estimate / rule of thumb (which is why it's so useful), not a precision instrument. But hey if you want more precision than the FPR we can do more precision: https://pavementinteractive.org/reference-desk/design/design-parameters/equivalent-single-axle-load/ https://pavementinteractive.org/reference-desk/design/design... As the link notes, road engineers usually work in LEF/ESAL (ratio to a standardised 18000lbs axle load), and provides some conversion tables. Assuming a relatively large 4000lbs sedan this is 2000 lbs per axle, or 2x0.0003 LEF = 0.0006 LEF. A fully loaded truck would be ~0.3 for the 12000lbs front axle, and 1.11 for each of the rear tandem axles, for a total of 2.52 LEF. 2.52 / 0.0006 = 4200. Which shows that the fourth power rule's 4096 was pretty close but if anything underselling it.

jessaustin 7y ago
Yeah, they use dual tires so that they don't pop catastrophically, not to spare the road from wear.
- reitzensteinm 7y ago
  I'm sure that's true, but are you saying it doesn't reduce wear?
  - masklinn 7y ago
    I'm sure it reduces wear on the tires.
    - reitzensteinm 7y ago
      "The AASHTO load-equivalency factors strictly apply only to axles supported at each end by dual tires. Recent increase in steering-axle loadings and more extensive use of single tires on load-bearing axles have precipitated efforts to examine the effect on pavement wear of substituting single for dual tires." https://www.fhwa.dot.gov/reports/tswstudy/TSWwp3.pdf https://www.fhwa.dot.gov/reports/tswstudy/TSWwp3.pdf