It’s one of the most famous buildings in the world - the Pentagon. Planning began before World War II – back when the military command was spread out over 17 different buildings all over Washington, D.C. So officers wasted hours every day traveling around from one office to another. And the problem was expected to get worse because the Department of the Army was expected to grow another 25 percent, enough to fill four more office buildings.

So architects were given just one weekend to come up with a plan for a building that would house the entire military and it was to be built next to Arlington National Cemetery. A major problem was there was a road that cut through one corner of the property preventing them from designing a traditional square building. So, they came up with the now famous pentagon shape.

And it was faster and cheaper to build than a tall building and because it had so many entrances – it would allow for nearly 20 to 30,000 people an hour to enter and leave the building. No skyscraper could have done that.

But with so many people coming and going it created another problem. Architects had to figure out how to deal with all the traffic that would bring all those people to the Pentagon every day. So they designed an elaborate system of over-and-under roadways arranged in cloverleaf shapes.  It allowed thousands of vehicles to drop off passengers and leave again without ever stopping for a traffic light.

It all worked so well at moving traffic to and from the Pentagon that when engineers began working on the Interstate system, they adapted the same idea for moving traffic from one high speed highway to another. So whenever you take one of those fancy clover leafs at an expressway exit – you can thank designers of the Pentagon.