The US interstate highway system is laid out following several rules. Knowing these rules can help you find your way from point A to Point B. The first and most helpful rule is the mile marker or “lollypop” which are on the right side of the highway in between cities and on both sides in the inner cities. These lollypops are usually little green signs spaced about a mile apart with a number on them. The number represents the mile mark of the highway. The numbers start at 0 on the far west and south of each state. So if you are traveling east on the 10 and have crossed the New Mexico border one mile ago you are on mile marker 1.
This can come in very handy in several ways. Most States have marked their exit numbers by the mile marker so if you are headed north and need to be taking exit 310 and have just crossed mile marker 179 you know you have 131 miles until your exit. Another use of these mile markers is confirming your direction. If you are on an even number highway and the numbers on the lollypop are getting smaller then you have confirmed that you are headed west. (Even number highways run east - west and mile markers start at 0 in the west and grow easterly). So with a odd number highway and the numbers are getting smaller you are headed south (odd number highways run north – south and mile markers start at the south 0 and increase northerly)
Of coarse there is always a highway marker sign at every on ramp so you can catch these signs which will clearly mark exactly what road you are on and what way you are going. A speed limit sign will always follow them, which is another good thing to check. Now I say most stated mark their exits by the mile marker, some states in the northeast are in the process of changing over to this method PA for instance.
Beltways
Many larger cities have a interstate beltway around them. You do not have to have a map to figure out how this works. The beltways are numbered by the highway they center around so for instance Kansas City. Lets say you are headed into Kansas City from the east on the 70 and you know you want to go to the 35 to head south at Kansas city to San Antonio to see David.. As you approach you will see a clearly marked sign pointing you to the 435. Knowing that the first even digit is just added to the number of the highway the beltway is centered around you can determine that you want to take this exit to the south and get on the 435 which will take you to the 35 for your journey south. (The 435 will intersect the 35 twice) I picked Kansas City for this demonstration since it is one of the hardest Cities to remain on the highway you are on through the town. They seem to like to combine all the highways together there and then have you scoot through lanes of traffic to find your exit back to where you were. Staying on the 70 through Kansas City is like a slalom course.
