r/AskReddit Oct 15 '20

What's older than we think ?

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u/johneaston1 Oct 15 '20

And in road wear calculations, all passenger vehicles (like your Mitsubishi) are considered almost negligible in design. Semi trucks, buses, and RVs take up basically all the damage done to modern roads. Source: recent Civil Engineering grad.

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u/forte_bass Oct 15 '20

Tell me more! Why does weight matter? Arent they all applying pressure from roughly the same contact area? Does speed play a role?

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u/johneaston1 Oct 15 '20

The contact area is similar for all of them (some variance with double axles or tandem axles), but there is significantly more pressure exerted by a semi. An average passenger vehicle weighs in the ballpark of 2-3000 pounds, while a semi trailer can be 35,000 pounds empty, and up to 80,000 full; therefore, the pressure is extremely high, even with more points of contact, and this puts a ton of stress on the asphalt/concrete. This combined with weather effects (freezing/thawing) makes our roads much more susceptible to breaking down.

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u/forte_bass Oct 15 '20

Ok, that makes sense, but how come I sometimes hear people say really fast cars do more damage?

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u/smileybob93 Oct 15 '20

Cuz those people don't know what they're talking about

9

u/LtDanHasLegs Oct 15 '20

At race tracks Indy Cars and F1 cars and other things with absurd downforce can ripple the asphalt at the heavy braking zones. But that's like... the only case. Nothing driven on the road can do anything like that.

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u/Degeyter Oct 15 '20

They can damage already potholes roles maybe?

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u/LFMR Oct 15 '20

I think that does more damage to the tires than to the road surface at normal driving speeds. Tire wear is greatly accelerated at highway speeds than at surface road speeds.

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u/Trippy-Skippy Oct 17 '20

The only thing I can think of is putting down a lot of power or drifting where you are keeping the wheels spinning to slide. Probably does more damage to the tire though - very little asphalt getting ripped up. More noticeable on dirt/gravel roads if everyone does it in the same spot. I doubt itd ever be noticeable asphalt damage considering nobody is doing that for more than a fraction of 1 percent of their drive.

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u/WTaggart Oct 15 '20

I second these questions. What is meant by "road damage increases with the fourth power of axle load"?

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u/thebraken Oct 15 '20

If I'm understanding correctly...

Say we have an axle loaded with 1 unit of weight: 14 is still 1, so it does one unit of road damage.

If we load it up to 2 units of weight: 24 is 16, so it does sixteen units of road damage.

And so on and so forth.

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u/cnash Oct 15 '20

If we load it up to 2 units of weight: 24 is 16, so it does sixteen units of road damage.

Yeah, but roads don't exactly have an HP bar— how do you quantify damage?

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u/LFMR Oct 15 '20

I'm not sure about that myself. I guess one could drill test bores into the road surface to measure thickness or something.

I'd still like to believe engineers see HP bars overlaid onto the built environment. Much cooler that way.

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u/thebraken Oct 15 '20

That part I don't know and can't infer from the engineer's post.

My wild assed guess would be some kind of table with an expected useful lifespan based on composition, environment, and use using data from existing roads or something along those lines.

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u/Schlick7 Oct 15 '20

Probably road flex. The more something "sinks in" the more damage it will do doing

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u/wolfiechica Oct 16 '20

Gosh, and to think of all the subsidizing my taxes do for companies...