How are they numbered?
The United States Interstate sign is a red, white and blue shield and has the word “interstate” on the top, the state housing the interstate, and the route number.
Interstates are one, two, or three digit numbers. If a interstate has a “0” at the end, (examples: 40, 70, 90) the interstate is running from east to west. If an interstate has a “5” at the end, (examples: 5, 15, 35, 95) it runs from south to north. The interstates are numbered going from west to east. Interstate 5 is on the west coast, I-95 is on the east. Interstate 45 is running up the middle of the country. The east-west interstates are numbered starting with the south. Interstate 10 is running at the bottom of the country, while interstate 90 is running at the top. I-40 is running through the middle. If the interstate is a three-digit number, then it is a route that either is a spur or a circle around a specific space. (examples: 495, 240, 305) The end two numbers depends on what the parent interstate is. For example, if there is a route coming off of interstate 94, a three digit route may be 794. The first number depends on whether the interstate is a circle route (connects back to the parent interstate twice, making a circle) or a spur route (has only one end connecting to the parent route). If the first number is a even number, then it is a loop route. (examples: 440, 836, 205) If the first number is a odd number, it is a spur route. (examples: 770, 515, 926). There are other routes that do not end with a “0” or “5”. It is still the same rule, if the last number is a odd number, it runs north to south, if it is a even number it runs east to west, it is just it does not span the whole country.
Business routes are loops or spurs around a city that have the same parent number as the interstate it is coming off of. The sign is a green shield with the word “business” at the top, whether it is a loop or spur, and the parent route number.
Here are some real-world examples of what I just explained above.
I-40 is probably the best example because it covers everything I just talked about.
I-40 goes from California to North Carolina, (east to west) therefore the last digit is a zero. There are many spur or loop routes coming off of Interstate 40. An example would be in Nashville, Tennessee. There is a I-840 and I-440. They are both loop routes, because the first digit is an even number. In Fort Smith, Arkansas, there is an interstate 540. This interstate is a spur route and only has one end connecting to I-40. In Winston Salem, North Carolina, there is a I-40 Business loop around the city.
I-95 is a interstate running from Florida to Maine, going north to south on the east coast, hence the name, 95.
Interstate 95 goes the whole way up the country, going from the most southern point of Florida (Miami) to the border of Maine with New Brunswick, Canada.
Interstate 95 goes through a total of 14 states, not including Washington D.C. It goes through many large cities such as Miami, Richmond, Washington, Baltimore, Philadelphia, New York, and Portland.
I-95 is the parent of 24 interstate routes. There are two city loops and one spur route coming off of I-95 just in Washington, D.C.
I-27 goes south from Amarillo to Lubbock, Texas. Since it does not end with a “0” or a “5”, it does not span the whole country. The end number is a odd number, so that means it runs north to south.
The US highway system is over 160,000 miles in total that is somewhat similar to the US interstate system. The US highway system is also very different. The odd numbers are usually run north to south, (example: US-21 runs from Columbia, SC to Charlotte, NC, which is north to south.) which is the same as the interstate system. What isn’t the same is that the smaller numbers in the US highway system start on the east. (US-1 starts in Jacksonville, FL and US-101 starts in Los Angeles, CA). The even numbers, just like the interstate system, run from east to west, but unlike the interstates, the lower number is on the canadian border while the higher ones are at the gulf coast and Mexico. (US 2 is against the Canada border while US-98 is at the bottom of the country. The most major routes usually end with a 0 or 1, but there are many exceptions to this (US-51 goes from the southern part of Louisiana to almost the Michigan-Wisconsin border. An acception to this would be US-25 which runs from Georgia to Ohio. There are also, just like the interstates, spur, loop and business routes. There are also “alternate” routes and “direction” routes.
Business routes (US highways)
Business routes are pretty much exactly the same as interstate business routes, they are spur or loop routes off of a major US highway. The only thing that is different is, well, there’s a lot more of them. In a town called Sedan, Kansas with about 1,000 people (as of 2017), has a business route going through it (Business US-166).
Another thing that US highways and Interstates have in common is loop, spur, and parent routes. They work a little bit differently though. Just like interstates, a 3-digit US highway has a parent route. You find the parent route by looking at the last two numbers of the 3-digit highway (Example: the parent route of route 643 would be 43). The 3-digit route does not necessarily have to connect directly to the parent route. It can run closely beside it or just be connected by other routes. Technically, route 936 could be across the country from route 36, it would just have to be connected by other highways. US-395 runs closely to the left of US-95. US-422 is directly connected to US-22 in Pennsylvania. US-431 is only connected to US-31 by other routes, not directly.
Story by Ryan Oast
Image credit: https://upload.wikimedia.org/wikipedia/commons/e/e9/Greensboro_road_signs.jpg