Suppose a time comes when you need to make your way across the country without luxuries such as a GPS. Those convenient little devices have spoiled a lot of people over the years. I have always kept a road atlas in my vehicle and always will. It is a very thick and detailed one that covers the entire country. Without it, however, I am still confident that I can eventually get to where I need to be. It is all a matter of knowing the interstate system and selecting roads that correspond with where you want to go.
The interstate system in the United States is officially known as the Dwight D. Eisenhower System of Interstate and Defense Highways. Creating it began in the 1930's but it was not until 1952 that Congress approved funding and the real fun got underway. By 1956, a uniform system was adopted. This included guidelines as to things such as access, speed allowance, and the number of lanes and this width of those lanes. It also took into consideration the space allotted for shoulders alongside the interstate.
A numbering system was put into place as well, and it is this numbering system that can get you to your desired location if you apply it to your travels. Interstates with odd numbers always run north and south. Those with even numbers run east and west. If you are travelling a north and south interstate in the west, it will have a lower number than a similar interstate on the east side of the country-for example, I-15 is toward the west coast while I-81 is on the east. When travelling east to west, you will find lower numbers in the south, such as I-10 being the southernmost interstate in comparison to I-94 in the far north.
Some interstates that pass through major cities also utilize a loop system, or beltway, which allows for avoiding the heart of the city and thus the traffic there. These are expressed in three digit numbers. For example, the I-210 loop goes around Lake Charles, Louisiana. When there are multiple loops or beltways off of the same interstate in the same state, the numbers increase as the loops increase. In this case, 210 is on the western side of the state of Louisiana, but when you get to New Orleans, you will come across the 610 loop. Both of these cities, and thus their loops, are off of I-10, hence the 10 in the number. The loop numbers are lower in the west and rise as you travel east. These loop numbers are re-used in each state, however, so there could be a dozen 610's around the country.
Interstate exits are also numbered in one of two different manners. Some of them are numbered by mile marker, starting at the most western or southern point. In that case, exit 36 will fall near mile marker 36. If there are three exits in the area of mile marker 36, they will be numbered 36A, 36B, and 36C. The mile marker exit system is handy because it allows you to know how many miles you are into a particular state and how many miles from one exit to another. Also used is a consecutive number system. It starts at the most western or southern point, but it numbers exits in order as they exist rather than by the mile, beginning with the number one.
If you are aware of how the interstate system works, you will always have a general awareness of where you are in the country. You will also be able to judge which interstates you need to take to get to another region of the country. Knowing which loop exit number you are at can also help you figure out where you are in a state. Having a working knowledge of the interstate system will be very useful in a SHTF situation if you have to travel to allies in another part of the country and GPS is no longer capable of taking you directly to their door. They don't call it a system of defense highways for no reason; knowing them can someday help you defend yourself.