Compton's speed hump jolts only fast cars

As Chancellor of Washington University in St. Louis, physicist Arthur Holly Compton — who had already won the 1927 Nobel Prize in Physics for his work on electromagnetic scattering — grew concerned about cars speeding along Hoyt Drive past Brookings Hall, a route busy with students on foot. The standard fixes were the same ones any campus or municipality would reach for: post a lower speed limit, add signage, station a patrol officer to write tickets.

All of those depend on a driver noticing the sign or fearing the patrol in the moment, which is exactly the behavior that was already failing. Compton instead treated it as a physics problem: rather than ask drivers to slow down, engineer a road surface that made going fast physically unpleasant enough that any car doing so would jolt its suspension, while a car already near the safe speed would pass over it smoothly.

In spring 1953, Compton designed and had installed along Hoyt Drive what the university's own staff called the 'Holly hump' — a raised pavement bump engineered in two variants, single- and double-humped, sized so that a typical early-1950s sedan traveling at a safe speed would ride over it comfortably while one traveling faster would be jarred hard enough to force the driver to slow down on their own, no signage, ticket, or patrol required.

Built a raised hump sized so safe-speed cars ride smoothly while faster cars are jarred, making the road itself enforce the limit without signs or patrols.

The hump's dimensions were calibrated so safe-speed cars ride smoothly, while faster cars get jarred.

The physical jolt forces drivers to slow down without needing to notice a sign or fear a patrol.

The mechanism works continuously and identically for every driver, with no ongoing enforcement cost.

When compliance depends on attention, embed the rule into the environment so non-compliance is automatically punished.

The humps worked well enough to become a fixture of the campus and were remembered fondly enough in Compton family letters that his wife, Betty, was recorded praising them; two of the original single-hump designs were reconstructed on Hoyt Drive in 1992 to mark Compton's centennial, decades after the originals had been removed.