Unsure of the proper flair, so engineering it is.
In: Engineering
They build them to withstand thousands of cars driving on them daily. Asphalt is resilient and cars move fast across it.
About 60% of the US interstate is made of concrete, these roads can last for 60 years and are poured thick so they are very slowly wearing over time but rubber is soft and concrete is not.
Because it’s designed to withstand it. There are typically three or four layers to the road and each layer can be up to one feet deep. And it costs about 3-6 million per mile for 2 lanes.
Because of the hardness of the concrete compared to the tires, the tires give up first leaving parts of the tires on the road.
If your wheels were made of metal the road will wear faster than the wheels.
Of course the road is not perfectly even and there is a chance the wheels will pull up tiny bits of rock/concrete from the road but are very small.
This is the same reason why we use diamonds for cutting tools, they are super hard and they wear the other material first.
A good example of this is the Jerry Rigs Everything YouTube channel where he tests the hardness of phone screens using different materials.
Since the tires are softer than the road the tires break down on the hard surface producing huge amounts of pollution.
Something like 80% of the micro plastics in the ocean are from tire wear.
Asphalt is made up of stones held together with bitumen, the bitumen is soft like tar so it can flex slowly. The size of the stones is selected so, when a weight is applied, they interlock together.
This combination means an asphalt road is flexible and won’t crack and can also carry a lot of weight.
The top layer of the road, caller the wearing course, contains stones specially selected to be hard wearing so they erode away very slowly.
They’re also selected for differential wearing, which means that, as they erode away, they don’t get polished smooth. A polished smooth road would be slippery and dangerous ofc.
Because the bitumen is soft, you can go at night and slice the top 40mm of the road off and put a new wearing course in. So the asphalt lasts a long time and is very easy to refresh.
This is why roads are made of either asphalt or concrete, anything else will be worn down within a matter of days if not hours. But even so roads requires regular maintenance and repavement
Eli5 version is that rubber soft, road hard.
That being said. Road does wear out just disproportionally slower than rubber, so it still needs maintenance and resurfacing every few years or so.
Also, I haven’t seen anyone else mention the fact that the road wear caused by Passenger Vehicles is almost entirely negligible.
Semi-Trucks and larger vehicles cause ~95% of the road wear even though they only make up roughly 10% of the traffic.
Also worth mentioning in addition to the other points: A highway is built to much higher standards than the Main Street of your town, which is built to a higher standard than a back country road, which is built to a higher standard than your neighborhood road, all precisely because of the amount of traffic they’re expected to handle.
A highway needs to be built to handle thousands of cars and trucks going 70mph (112km/h) per day, whereas a neighborhood road only needs to be built to handle one family crossover going 15mph (24km/h) every half hour or so.
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