Cats Eyes

Ever wondered where those reflective “lights” come from on our roads – they are called “cats eyes” and for a reason.

Cats, like other animals have different eye structures to humans. When a human has a photo taken with a flash, there is often what is known as “red eye”. This is because the rear of the human eye is the retina and this is made up of a mix of blood cells, so when the light is reflected, it is the colour of blood. Cats though, have a layer behind the retina called tapetum lucidum. This is basically a mirror that reflects all the light back to the retina, so that the animal can get a better picture. Most nocturnal animals have this natural mirror. Subsequently, a greater amount of light comes back to the viewer, in our case, a human.

Back in 1934 in northern England, Percy Shaw, an engineer and amateur inventor, realised that the shiny strips of tramlines had been helping him find his way around the local area. When these were removed after the tram system shut down, he had a problem seeing where the road went in the distance. Six years earlier, Richard Hollins Murray, who owned a company in Manchester had patented a reflective glass bead, in the mode of a cat’s eye specifically for advertising signs!

Shaw took the reflector that Hollins Murray had invented and created a unit that could be embedded into a roadway with two beads per unit – the reflective properties then looked like a pair of eyes. The unit actually looks more like a squashed spider than a cat’s head!

Shaw’s design was quite clever in another way. He created an outer steel shell to protect the unit and then fitted the beads into a rubber mounting that would press down into the chassis when a vehicle rolled over it. In front of the beads is a rubber flap that scrapes any dirt off the beads when the rubber mounting is depressed, thus cleaning it.

Shaw patented his design – with reference to Hollins Murray’s bead – in 1935 and created a company to manufacture them. Prior to this, he had run a road repair business, so knew how to combine the catseye™ (as they were trademarked) into the road surface. World War II helped Shaw’s company because there were black-outs every light and the road-stud (it’s official name) allowed drivers to see the road with the dimmed headlight power on vehicles.

From the UK, this very simple idea spread globally with different colours for different purposes – mostly on motorways and freeways where red denoted the outside edge of the road, an amber colour denoted the central reservation and green for junctions. Other countries used different combinations of colours sometimes based on local weather – snow typically means red stands out more.

It’s such a simple design, taking a product and reworking it for another purpose and they have stood the test of time.