In 1956 President Dwight D. Eisenhower championed the institution of the Interstate Highway System, citing the German Autobahn as inspiration, and the logistical necessity to move ground troops quickly in the event of a national emergency. Today the 46,800 mile network of highways collectively comprises the largest road network in the world.
But as you're driving across America, have you ever wondered to yourself what the road signs - the numbered highway markers - actually mean? Believe it or not, roads are not assigned some random highway number for kicks, but are instead part of a vast numeric system that can actually help you navigate yourself across the country. Fancy, huh?
- Primary Interstate highways are assigned a one or two-digit route number less than 100. Highway numbers that are divisible by 5 are considered to be major arteries of the system, carrying traffic great distances across the country like I-80 or I-35.
- Highways assigned an even number run East to West, starting with I-10 through the Southern states increasing to I-90 through the Northern states.
- Highways assigned an odd number run North to South, starting with I-5 which runs along the West Coast increasing to I-95 which runs along the East Coast.
- Spurs are offshoots from the main highway which often terminate in an urban area. They are generally assigned a three digit route number with the first digit being ODD to indicate it as a spur, such as I-394 in Minneapolis. Be careful with spurs, because they'll often abruptly drop you off in the middle of downtown.
- Loops are auxiliary routes which often by-pass an urban area and connect with the main highway at a later point. They are assigned a three digit route number with the first digit being EVEN to indicate it as a loop, such as I-680 in Omaha. Loops are often helpful in navigating around busy rush-hour traffic in an urban area.