Look at these yokes on the road. What do you call these? You might call them Stimsonite
markers or road studs but over in my country - which is Ireland, and in the country they were
first invented - which is England; we call these "cat's eyes". Despite their constant presence in
your life, you've probably never really given them a lot of thought, similar to politicians,
preachers and proselytizers. The difference is cat's eyes are content to just do their thing
without bothering you - they never harass you on the street or come around looking for money or
buy a private jet with that money, and even though their design is surprisingly clever,
their history is interesting and their function is vital - you never hear them boasting about any of
that or complaining. So today, I will tell you why cat's eyes are awesome, because they won't.
Firstly, you probably know what these things are for. They reflect light to mark the boundaries
of the road in low visibility. It simply isn't, or at least wasn't, feasible to illuminate every
part of every road everywhere. So we put lights on the cars. These are great but they can only
light up the path ahead of you so far. If you can only see a few dozen feet ahead of you,
that might not be a problem if you're just out for a walk, but it is a pretty big problem when
you're travelling a few dozen feet a second. So cat's eyes are installed along the roads,
using reflective material to guide drivers through the darkness. But how does it work?
How can we so clearly see the cat's eyes in parts of the road that otherwise appear dark? I mean,
how is the car's light being picked up by the cat's eye but not the surrounding area?
Well, obviously, the cat's eye is more reflective than the surrounding area - that's the key here,
reflection. Instead of powering a bunch of light sources we can just reflect the light from one
light source - your car. Ok, so all they do is reflect light, that's easy, all we need
is a really reflective material, like a mirror and we just put a bunch of them down, right?
Well, ignoring the major issue of turning your road into a hall of mirrors, I mean you might as
well go ahead and paint tunnels on the walls and turn all the signs backwards too at that point,
there is a reason a simple mirror doesn't make a good road marker.
Why? Well, think about it, if there's a mirror on the ground and I shine a light on it,
the light is just going to bounce up into the sky. It might blind a helicopter pilot and cause
an accident. It might even be somewhat amusing, but it doesn't help me. We can't just have light
bouncing all over the place, what we really need is to send the light back from where it came,
so I can see it and not the helicopter pilot. This is called retroreflection and there are
a few different ways to achieve it, but today we'll be looking at how cat's eyes
do it. Like literal cat's eyes. If you haven't figured out by now these
things are named after the strange reflective property of cat's eyes, well, now you know.
Basically the back of the cat's eye is reflective, and it is in a concave shape meaning it'll often
send light back in the general direction it came from. So if we shoot a beam of light straight
down the middle, it'll come back, just like a mirror, but we can also point it downwards or
upwards into the surface and it'll still come back. There are still a few cases where maybe
the light won't come back the same direction, but the cat's cornea and lens will refract the
light in such a way that it converges on the reflector and now there are no more problems.
For cats and other animals that exhibit eyeshine, the reflected light passing back
through the retina gives them superior night vision, even if the process does introduce
some blurring. Thankfully we can manufacture things similarly to how cat's eyes are set up,
and stick two retroreflectors in a road stud - or a bunch of tiny ones like little beads. Hundreds
of cat's eyes - I have a tattoo like that. Interestingly, if you were to paint an eye
onto a concave surface like this, you get a strange effect where it appears as if the
eye is always watching you. Not hugely relevant, I just like to share things.
Cat's eyes were first created in 1934 by Percy Shaw of West Yorkshire, England. Shaw
noticed how difficult it was to drive at night after the tram lines in his area were removed,
realising how much he depended on the reflection from the rails to see where he was going. Inspired
by actual cats and their glowing eyes, he put two pairs of retroreflectors, which were first
invented six years earlier, also in England, in a rubber dome, one pair for both directions,
and mounted it in a cast iron housing. Calling them cat's eyes, Shaw had created a
very clever invention. The cat's eye was supposed to be partly buried in the road and set with some
form of tar mixture. The retroreflectors added visibility to dark roads and were protected by
the rubber dome. The rubber dome depresses into the ground when a car passes over it,
preventing damage to the car and the retroreflectors, and the iron casting forms
a kerb around the thing to take most of the car's weight, further protecting the retroreflectors.
This means that not only do cats eye's mark the road visually, but you can safely drive on them
and they'll give you a tactile warning that you're crossing a road boundary. Well, they're mostly
safe, although there was an incident in England in 1999 where a van dislodged the metal housing and
sent it flying into a following car, hitting the passenger in the face and killing her instantly.
Moving swiftly on, there is another genius quirk in the cat's eye's original design. When
the rubber dome is depressed, the lenses are wiped against rubber in the housing,
cleaning their surface. Actually the housing is designed to hold rain water,
so this wiping process is even more efficient. Percy Shaw had to do some convincing to get the
government in on his idea, but by World War II, Britain was enforcing blackouts, making sure there
were no lights on during the night, in an effort to hamper German pilots above. Cat's eyes proved
invaluable during this time, and they saw mass adoption across the UK before spreading worldwide.
As well as different forms and shapes, they can also be made in different colours,
denoting different boundaries on the road - like white for the lane
divisions and amber for the edge of the road. Now you're less likely to see their original
design in favour of these cheap plastic ones that are just kinda pasted onto the
road rather than buried in it. I feel like these ones are always coming loose but maybe not a big
deal seeing as it's just a bit of plastic. In 2006 the cat's eye was voted number seven
among Britain's most iconic designs. This list should be interesting. Let's see. Number 10;
the k2 telephone box, alright makes sense. Number 9; the Grand Theft Auto series, ok,
surprising but makes sense. Number 8; Tomb Raider, really? more iconic than the phonebox
and GTA? I don't think so... Number 7; the cat's eye, yes. Number 6; the routemaster bus,
yep that makes sense, what about the black taxi cab though? Number 5; the World Wide Web, that
will never catch on. Number 4; Margaret Thatcher, probably the worst design so far honestly,
no wait no it's actually the Mini at number 4. Number 3; the supermarine spitfire, cool.
Number 2; the london underground map, not the underground itself just the map. That made number
2 somehow. And number 1; the Concorde. Lots to be said both for and against that at number one,
I think, but that's what the comments are for. With our usage of electricity being a bit more
extensive than it was in 1934, we might see the importance of cat's eyes wane as more and more
roads are fitted with lights. Maybe cat's eyes will house solar-powered LED's instead of just
retroreflectors. They've already done this in some places, but I sort of feel like this is
an example of something that is becoming less cleverly designed over time than it
was originally. Don't get me wrong, obviously it's improved over time, but finally putting
lights in them is kinda like technologically brute forcing the problem, compared to a time
when we just had to make the best of what we had. I think this is a very elegant solution
to a problem that maybe we can just eliminate altogether today. Which is good, I just like this.
So what do you think? Can you still appreciate something even when it's been made obsolete? I
think the answer is yes, I mean people love vintage cars and retro video games
and mechanical watches and vinyl. I guess it just comes down to being able to say "this is better,
but I like this". And that's how I feel about cat's eyes. The old design is just
more interesting to me. Something about it just says "a human made this", y'know?
Well, if I've made you care about something that you see literally thousands of every day
without ever really paying much notice, I think that probably deserves a subscription right? If
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