The encyclopedia · Engineering & Operations · Technical decision · 1933-1935
Percy Shaw's cat's eye road stud reflected light and wiped itself clean
After tramlines vanished in fog, Shaw built a rubber-cased glass reflector that guides night drivers and self-cleans every time a tyre passes.
Reflecting Roadstuds Ltd
the move
On a foggy night in December 1933 Percy Shaw drove the steep winding road from Queensbury to Boothtown, near Halifax, using the reflection of his headlights on the tramlines to find his way. The tramlines had been taken up for repair, and in the sudden darkness he nearly left the road until a pair of cat's eyes shone in his headlights. He realised a reflecting device fitted to the road surface could guide drivers in any weather.
Shaw took out patents on his invention in April 1934 and incorporated Reflecting Roadstuds Ltd in March 1935, with himself as managing director. The design mounted glass reflectors in a rubber casing inside an iron box embedded in the road. The clever part was the rubber: when a vehicle drove over the stud, the rubber and glass were pushed down below the road surface and the motion squirted rainwater out, cleaning the lenses automatically.
Cat's eyes became critical during the Second World War, when streetlights were switched off and headlights were masked in the blackout, and the reflectors guided traffic where lamps could not. After the war, junior transport minister Jim Callaghan had them introduced across Britain's road network.
why it works
- A lamp needs power and wiring; a reflector needs only the light already hitting it
- The rubber pad turns every passing tyre into the cleaning mechanism
- Dipping below the road surface protects the glass from impact and grit
- One stud works on any road in any weather, so it scaled with no new infrastructure
what transfers
Make the infrastructure maintain itself: build normal wear and tear into the design so every passing unit cleans and preserves the thing it uses.
what came after
Cat's eyes spread across Britain after the war and are still in use on British roads today, with the original self-cleaning design unchanged in its essentials. Reflecting Roadstuds' factory in Halifax kept making them for decades, and the device is routinely named among the most important road-safety inventions. The idea that normal use can do the maintenance reappears across infrastructure design.
references
- Cat's Eyes — A History of the World
- Weatherwatch: Percy Shaw and the invention of the cat's eye reflector
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