Freeways, Expressways, and Interstates Cont'd

Numbering and Orientation

Expressways use a somewhat confusing numbering system to identify their location and function.

Remember, the overall goal is to move traffic quickly and efficiently, so each digit of the number, as well as the shape of the sign, convey important information.

Interstate highways are recognized by a blue shield-like sign with a one-, two-, or three-digit number listed on it. If the interstate runs EAST to WEST, the number on the sign will be EVEN. If the interstate runs NORTH to SOUTH, the number on the sign will be ODD. Sound easy? That part is. For example, you have even-numbered interstate 4 in central Florida, which runs east-west, but interstate 95, running from Maine to Florida, is odd-numbered.

Now, the somewhat confusing part:

For even-numbered (east-west) expressways, numbers begin in the SOUTH with single digits (interstate 4 runs across central Florida). These numbers get LARGER as drivers move NORTH. This is why they start in single digits in Florida, but are double digits (I-66) when they reach northern regions.

For odd-numbered (north-south) expressways, numbers begin in the WEST and get larger as they move EAST. This is why they start in single digits in California, but are double digits (I-95) by the time they read the east coast.

Now, for another wrinkle: Around cities, traffic flow is a bit trickier to plan for. Civil planners designated with a 3-digit number an alternate route which directs traffic around the heaviest traffic areas. Because many of these routes branch off of two-digit interstates, this 3-digit system was developed using some of the same digits.

Take an interstate bypass like I-664. The “I” obviously stands for interstate. The first “6” digit is even. This means that this alternate route branches off I-64 going AROUND the city.

Now, take an interstate bypass like I-164. This interstate begins with a digit which is odd –  the numeral 1. This means that the interstate bypass in this example goes INTO and often THROUGH a city.

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