Where GM has tested its cars since 1924: the Milford Proving Ground

The problem that built this place was a pothole. In the early 1920s General Motors engineers compared new cars by driving them out to public roads near Flint and running them over the same rough stretches — except the road crews kept tearing those stretches up and repaving them, so no two tests ever matched. You cannot tell whether a new shock absorber is better if the road under it changed last week. The fix was almost stubbornly simple: stop borrowing public roads, buy your own, and never let them change.

So in 1924 GM opened the Milford Proving Ground in western Oakland County — the first place any carmaker built purely to test cars, anywhere. It started modestly: about 1,125 acres, a couple of buildings, a few miles of track. Engineers could now run a car over the identical washboard, hill, and curve a hundred times and trust the numbers.

A century on, it is still going, sprawled across thousands of acres of roads, grades, and trick surfaces — banked high-speed loops, cobblestone torture lanes, salt baths and dust pits, a ride-and-handling course that has shaped how Chevrolets and Cadillacs feel under your hands for generations. Most of that work happens out of sight on purpose; a future Corvette tested in plain view is a future Corvette photographed by a rival.

You cannot drive in — it is fenced, guarded, and very much working. But it is a strange and quiet bragging right for a township most people pass without noticing: GM has been proving its cars on these few square miles of Michigan longer than almost anyone on earth has been proving anything.