America added 3,400 car washes in six years. The benchmarks say where the next ones fit.

Back in April we published the five location signals that predict car wash success. This is the follow-up with the numbers — because the biggest thing that's changed in the category isn't demand. It's supply.

The boom, counted

Employer car wash establishments in the U.S., from the Census Bureau's business patterns data:

That's 23% more car washes in six years — the fastest establishment growth of any category we track, driven almost entirely by the express-tunnel membership model. Employment grew far slower (154,000 → 167,000), which tells you what kind of car wash is being built: high-throughput, low-labor tunnels.

Source: IQ Locations analysis of County Business Patterns, 2017–2023.

A 23% supply expansion means the average new site opens into a materially more competitive map than the same site would have faced in 2017. The demand signals from the April guide still hold; the margin for error around them has shrunk.

The demand-side benchmarks

The customer unit for a car wash isn't a person — it's a vehicle, plus the income to pay for its upkeep. Two numbers put any trade area on the national curve:

Two-plus-vehicle households. In the median American neighborhood, 61% of households run two or more vehicles. Nearly a third of all tracts — 26,030 of them — sit above 70%. Those are the multi-car suburbs where a monthly membership covers the household fleet, and they're the natural center of the express model's map.

The carless tail. At the other end, about one neighborhood in ten has 20%+ of households with no vehicle at all (we'll map that fully in two weeks). Every percentage point of carless households is addressable market that doesn't exist, whatever the traffic count claims.

The working benchmark: a tunnel trade area wants to sit meaningfully above that 61% two-car median, on an arterial the vehicles already use, with the household income to make $25–$40 a month an unexamined line item — the middle band and up, not necessarily the top.

The saturation math nobody runs

With 18,705 washes against roughly 26,000 heavy two-car tracts, the obvious question for any new site is how many memberships the surrounding tracts can still support. The arithmetic is unglamorous: vehicles in the ring, times a realistic membership capture, divided among every existing tunnel plus yours. A 23%-grown category has already claimed the easy corners — the sites that pencil now are the ones where the vehicle density is real and the split still leaves a full book.

That's a fifteen-minute exercise once you have the tract-level vehicle and income data, and a 30-second demographic report is where it starts. The alternative — trusting that a boom category has room for one more — is exactly how booms end.