Today's Why Guy question is from Autumn Kelly Bradley: "Why are the highways numbered the way they are?"

Great question. We drive the highways daily and probably never wonder why it's numbered I-5 or I-80. 

There's actually a system that was put in place in 1956 called the "Federal Highway Act." Superhighways were built to open up the USA to a new dawn of happy motoring — America on the move.

Here's how numbers were assigned, thanks to President Ike Eisenhower, a.k.a the “Father of America’s Highway system."

Interstates running north to south were given odd numbers with the lowest numbers starting on the west coast with I-5, I-55 in the midwest and I-95 on the east coast connecting Maine to Florida.


Interstates running west to east were assigned even numbers with the highest numbers given to the north, I-70 and I-80, and the lowest east to west route in the south, Interstate 10.

America's 48,000 miles of Interstates have allowed for more travel and relocation to suburbs, particularly in the Western U.S. If you look at a U.S. map as a body, the highways are the veins that allow our blood to flow. 

It’s vital to our growth.

"...The Interstate is a linear economy-on-wheels, a distinct and self-sustaining 51st state, in a sense, that generates life and commerce," wrote Peter Kilborn in the New York Times.

So, the next time you're on I-5 or I-80, know that some thought went into that number, and it wasn't just some random digit pulled out of Uncle Sam's hat.


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