This is a fascinating working paper by Taylor Jaworski and coauthors about the Interstate Highway System. eh.net/eha/wp-content… Get ready for a few facts and findings.
The Interstate Highway System is composed of almost 50,000 miles of highway, made with over 1.5 billion tons of aggregate and 35 million tons of asphalt, and 48 million tons of cement, built since 1956. 
In 1945, the average driving speed on the then-existing intracity road network was 45 miles per hour. Today, as we all know, it's routinely above 70 miles per hour.
Using their fancy schmancy structural/GIS model calibrated using Rand-McNally Road Atlas data, the authors find that the Interstate Highway System reduced travel times by an average of 30 percent from 1960 to 2010.
The really cool thing about the authors' model is that it enables them to calculate the value of individual segments of Interstate by just estimating the counterfactual where it doesn't exist.
The numbers are absolutely mind-boggling. If I-95 didn't exist, they estimate aggregate income in the US would be $277 billion lower PER YEAR. Since it costs $4-10 million per mile to initially build an Interstate, this is a massive free lunch.
The 10 most valuable Interstates are I-5, I-10, I-35, I-40, I-70, I-75, I-80, I-90, I-94, and I-95. The least valuable of these (I-40 and I-94) produce around $80 billion in social value annually.
On a per-mile basis, I-78 takes the cake, producing $294 million *per mile per year* in added income. Ihis means if you had to completely rebuild it every year from scratch, it would still generate a 30x ROI.
These staggering figures are with "only" a 30% speedup versus the non-Interstate road network. Now imagine what the social value of hyperloops, hypersonic aircraft, and eVTOL aircraft. When your travel time goes down by another 80%, what will the value be?
Imagine if the US could build high-speed rail for $30M/mile like the Chinese can.
Oh look, @taylorjaworski is on Twitter now, I’m sure he’d be glad to answer questions about his paper.
