Comment by xnyan

12 hours ago

>They don’t replace nearly enough cars and SUV’s to make up for the difference in fourth power of axle weight

A modest bus holds 40-50 people. Most commuter traffic is single driver, single vehicle. I don't know to which power the difference in axle weight would have to be to surpass the efficiency gains of replacing 40 to 50 American sized SUVs with a city bus, but I suspect it's more than four.

3 comments

xnyan

XCabbage 4 hours ago

At the heavy end, SUVs weigh about 3 tonnes, while at the light end buses weigh about 12, a 4x difference. 4^4 = 256. So if the claim about the fourth power is true, you'd need to replace 256 SUVs to break even on wear, which is obviously impossible.

(I don't really understand how the fourth power of axel weight thing can possibly be true, though. Why would joining two vehicles together into a mega vehicle with double the weight and double the wheel count suddenly cause the combined vehicle to inflict 16x more wear than before you joined the two together? It makes no sense.)

rkangel 2 hours ago

Joining two vehicles together with double the weight and double the axle count does not change the load on each axle.

So, scenario A:

    4 ton vehicle, 2 axles
    load per axle is 2 tonnes.
    2^4 is 16
    2 axles - so load is 32.
    Another vehicle the same - also loading 32
    Total: 64

Scenario B:

    8 ton vehicle, 4 axles
    load per axle is 2 tonnes
    2^4 is 16
    4 axles - load load is 64
    Total: 64

philwelch 14 minutes ago

Another example I worked out once
A Ford F-150 weighs about 2 tons and has two axles, for an axle weight of 1 ton. 1^4=1.
A garbage truck weighs maybe 30 tons and has three axles, for an axle weight of 10 tons. 10^4=10,000.
So if you drive an F-150, you’re doing as much road damage driving down the street 10,000 times as the garbage truck does once. Rural areas that don’t have garbage trucks and just expect everyone to haul their garbage to the dump in the back of their pickups are onto something.