Comment by philwelch
20 hours ago
Buses are implicitly subsidized by road maintenance spending. Road wear and tear occurs according to the fourth power of axle weight, which effectively means almost all of the wear and tear is incurred by the heaviest vehicles, which include buses.
Axle weight and vehicle weight aren't the same (or even very closely correlated). A bus will weight ~3-4x more than a car, but has wider tires, and carrying far more people. As such the weight of a bus is likely similar to or lower than an equivalent number of cars.
Wider tires do not reduce axle weight.
Here in Seattle, the busy roads with older lanes used for buses are obvious, because they have two deep canyons while the lane next to them is fine. In fact King County Metro has to pay millions in fines to the state because the buses are excessively heavy.
No roads without bus traffic have the same type of damage.
Roads still need maintenance even if nobody uses them, so a significant portion is split evenly across all traffic.
Busses are light compared to 18 wheelers and other heavy equipment, they also replace many cars and SUV’s which keep getting heavier.
Finally that rule of thumb isn’t really that accurate, “A 1988 report by the Australian Road Research Board stated that the rule is a good approximation for rutting damage, but an exponent of 2 (rather than 4) is more appropriate to estimate fatigue cracking.” Rutting really isn’t that significant in most cases, but can instantly destroy road surfaces when fully loaded construction vehicles etc drive over something once.
> Roads still need maintenance even if nobody uses them, so a significant portion is split evenly across all traffic.
Your former doesn't imply the latter. Here in Seattle we even still have cobblestone roads without heavy traffic and they spend very little money on them.
We have extensive rutting damage on the lanes use by busses and requires more expensive, deeper road base when they get replaced. This cost is due to the heavy traffic.
Even if squared, the buses are still 22 tons instead of 2-3 tons. 49 times more damage isn't good.
22 tons are huge busses and overkill unless you actually need that much space, and tend to have 4 axles. ((22 / 4)/(3/2)) ~= 13.5x a heavy SUV but could be replacing 30+ vehicles.
> Busses are light compared to 18 wheelers and other heavy equipment, they also replace many cars and SUV’s which keep getting heavier.
They don’t replace nearly enough cars and SUV’s to make up for the difference in fourth power of axle weight. But yes, 18 wheelers are worse.
>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.
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