From: https://www.fhwa.dot.gov/infrastructure/target.cfm
The 37,700 mile interstate highway system was supposed to cost $23.2 billion.
That works out to $615,000 per mile.
Latest I-75 construction near me:
When did construction begin: Early 2023
Length of road under construction: 1.3 miles
Construction cost: $97 million
The expected completion date: Summer 2026.
That’s about $75 million per mile.
The inflation adjustment factor 1955 to 2025: 32.09
So $615,500 should cost $19.75 million today.
The projection is only 97/19.75 = 492% off.