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The hidden logic behind US interstate numbers

HERE’S THE INTERESTING PART

The government actually organized its massive concrete network with a rigid mathematical grid, completely ignored by most drivers. Odd digits run north to south, while evens run east to west. If the number divides evenly by five, it is considered a major cross-country route. It is a brilliant layout mostly wasted on people who just follow whatever their navigation console dictates.

The hidden logic behind US interstate numbers
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