I'm not an expert when it comes to roads and highways. I mean, usually we talk about bike lanes around here. But today I learned, via Brian Potter over at Construction Physics, that there is such a thing as an International Roughness Index (or IRI). In simple terms, it measures how much a car bounces up and down over a given distance of driving, and it is usually expressed in units like "millimeters per meter." A low IRI is good. It means less bouncing up and down. And a high IRI is bad. It means more bouncing up and down, suggesting the road is poor. This, it turns out, is the most commonly used index in the world for evaluating whether a road sucks or not.
And in this recent post, Brian uses the index to chart out road quality across the US. Here's non-interstate roads for the 19 largest metro areas:
In may ways, this recent article by Brian Potter about how fast cities can grow, feels intuitive: Small cities tend to grow faster than big cities (on a percentage basis) and, as cities get bigger, their growth rates tend to decline. It is, however, still interesting to see the data behind this intuition:
A city of less than 100,000 might be able to have growth rates of 10-20% or more, and cities of up to 3-400,000 can potentially have growth rates in the neighborhood of 10-15%. Potential growth rates tend to fall as cities grow larger, and cities above 1 million people almost all grow at less than 10% per year, and usually less than 5% per year. The US, the Middle East, Southeast Asia, Africa, and South America all seem to have followed this basic pattern, assuming the data is reliable.
It is also a good reminder just how much of an outlier China is:
Unsurprisingly, since 1950, Chinese cities have mostly exhibited higher growth rates than US cities. Only around 12% of US data points are above a 5% growth rate, whereas for China this is close to 50%. China also has 2.5x the fraction of cities growing above 10% per year, and 3.3x the fraction of cities growing above 15% per year.
And some cities are outliers even within China. The most notable here is
