This is 99% invisible. I'm Roman Mars.

If you listen to the show for a while, you know that we're big fans of icons and symbols and signage,

and one of the main places you encounter those is on the road.

So in our ongoing ubiquitous icon series, we're taken to the highways.

I'm thinking we should call this one Highways 101 you know I like it.

I like it Highways 101 that's Kurt Colstead he's our digital director and

co-author of the book the 99% of physical city. One of the things Kurt does is he checks our inbox

for listener submitted ideas, combs to all of them.

And earlier this summer, a 99-PI fan

named Daniel wrote us about a strange stop sign that he encountered while traveling and you started

digging into this story.

Yeah, so his email started like this.

A couple of years ago we took a trip to Hawaii and my wife became obsessed over a few blue stop signs we saw in parking lots.

The signs were the size and shape and used the same lettering as normal red stop signs,

but they were bright blue.

So I don't think I've ever seen that before.

I had never seen this either, either in images or in real life.

So I started looking into why some were blue and that turned out to be pretty easy to figure out, but it got me wondering something a lot more fundamental, which is why are the rest of them all red, right? Like. Why is that such a thing in the first place?

Totally. Yeah, and that got me into, of course, digging into the whole history of stop signs.

Of course, of course, that's the only way this is going to go with you.

Yeah, it's just my nature. And as I was looking into this, this one figure kept popping up

everywhere I looked, a guy named William Phelps Eno, who in the early 1900s became

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