ElI5: why is it that we tend to have more pot holes on street roads but not many on freeway or highways?
In: Engineering
Standards. A leading cause of potholes is from water getting under the road. This causes the road to “float”, or the supporting soil to erode. This can almost always be avoided with better planning and implementation. But that could be prohibitively expensive. Sometimes it is more expedient to expect frequent repairs.
Highway roads gets often built in a higher and much more sturdier quality than street road and get more maintenance to fix pot holes
For higher speeds pot holes are much more dangerous, so it’s much more important to fix them on highways.
Number one cause of potholes is water and weight. A highway is built to take more weight and engineered with better drainage. Local roads often flood or have puddles and are engineered to take less weight and heavy objects spend more time on a particular area
There is probably a metre of engineered fill and a couple of hundred mm of asphalt of bound pavement on a highway vs 150-200mm of gravel and 20-30mm of asphalt on a public street. Also better drainage to prevent water getting under the pavement.
Maybe a lot more streets than highways.
In the US there are 47,432 miles of Interstate Highways and 4.09M miles of roadways.
When you add up every single navigable road in the US, you get approximately 4 million miles. Out of that, only 47,000 miles (1.2%) are interstate highways. You can see how maintaining this colossal network of city and suburban roads is a big undertaking for local municipalities.
Highways are far more manageable and are usually maintained by state governments.
Many highways, and especially toll roads, are managed by private contractors who are contractually bound to maintain their stretch of road.
Interstate highways and highways are built differently than your average city street and are better maintained than a city street because they have that much more traffic that will be traveling at higher speeds.
They have better drainage due to not being hemmed in by sidewalks and curbs.
And if they do start to develop any type of defect, it’ll be patched asap.
I71 in my stretch of ohio is straight full of pot holes. If you hit them with so much speed you barely notice, or just avoid those lanes untill after the merge.
A few contributing things:
A lot of motorways and high speed roads were purpose built from scratch to relatively modern standards. A lot of country and town roads are just paved over old 19th century (or earlier) roads. Foundation problems apply to paving as well as buildings.
Town roads have water, gas, power, sewers and telecoms buried in them, which needs to be dug up and worked on from time to time. A lot of potholes originate from the repairs done to the road surface not being done properly and then the surface breaking up.
Finally, a pothole on a 70mph road is a very high priority item for the maintainer of the road and needs to be fixed asap – sometimes necessitating an immediate lane closure. Potholes on lower speed roads can be tolerated for days or weeks while the maintainer gets around to fixing them. If the pothole exists for less time, you’re less likely to actually see it.
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