depends on where they buy fuel... when my son was driving for CFI and going cross country alot, they would have all his fuel stops mapped out for him to minimize costs. of course a tractor trailer causes considerably more wear to a roadway than what it pays per mile for fuel, so you got that too... but basically a bicycle causes zero..
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Considering that the truck has eight axles and the sedan has two, the relative damage caused by the entire semitruck would be 625 x (8/2) -- 2,500 times that of the sedan.
“The damage due to cars, for practical purposes, when we are designing pavements, is basically zero. It’s not actually zero, but it’s so much smaller -- orders of magnitude smaller -- that we don’t even bother with them,” said Karim Chatti, a civil engineer from Michigan State University in East Lansing. https://www.insidescience.org/news/...g that the truck has,times that of the sedan.
Probably the largest component is weight per sq-in of contact on the road, and you are right, a bicycle would cause very little because a 200lb person on a bike with a 3" wide tire is putting down say 11.11lbs per sq-in, assuming a 3x3" contact patch.
An axle with no load rolling down the road is causing very little wear because the contact patch is considerable with very little pressure on it, so you are imposing very little displacement of the asphalt surface. distilling it down to number of axles doesn't adequately capture this.
A 5,500lb pick-up, like my wife's, has a P285/45R22 tire, which is an 11.2" wide tire, we'll say 11" for the sake of this exercise, and the patch is say 8" long, so 88sq-in, 15.6lbs per sq-in.
We are assuming a uniform pressure distribution for the sake of this exercise, it of course won't be, the centre of the contact patch will be higher pressure than if you were to measure it forward or rear or the centre.
An 80,000lb fully laden semi has a typical tire size of 295/75R22, so an 11.6" tire. We'll say the patch is 6" long due to the higher pressure, so 70sq-in. Assuming a triple axle trailer and double axle cab that's 22 tires, 52lbs per sq-in.
So, the semi would cause 3.5x as much wear as my wife's truck.
Of course this changes based on the dimensions of the tires on the semi and the number of axles. A triple axle dump with the same tire dimensions as our semi and loaded to 42,000lbs is putting down 60lbs per sq-in, almost 4x our 1/2-ton truck example.
Does a fully laden semi burn 3.5x as much fuel as my wife's truck? Approximately, yes. So it's pretty comparable.