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September 10, 2013 > What do highway numbers mean?

What do highway numbers mean?

By Britney Sanchez

All U.S. interstate and highways have a set numbering system in which help designate the type of road it is and where it goes. There are three different categories: U.S. Highways, Interstate Highways, and State/Provincial Routes.

The highway numbering movement began in 1902 with growing tourism promoted by the automotive industry that influenced more people to travel long distances. There was no cohesive structure to highways until, in 1914, the American Automobile Association (AAA) created the American Association of State Highway Officials (AASHO) and the American Association of State Highway and Transportation Officials (AASHTO) with the help of federal legislation. More funding from the federal government in 1916 improved roads and a fundamental numbering system for highways was created in 1925.

All highways are numbered by the direction of the route. Highways running North/South are marked with odd numbers and East/West routes are given even numbers. U.S. Highways or "Federal Highways" are assigned a number ranging from one to three digits. U.S. Highways ending in "0" designate a route that stretches from coast-to-coast (with the exception of US 2).

U.S. Highways running North/South, however, end in either a one or five. On North/South routes, the number begins to grow larger traveling from East to West (US 1 on the east coast and US 101 in the west), while East/West running route numbers grow larger going from North to South (US 2 being in the north and US 98 in the south). Spur routes, smaller freeways off of larger routes, have three digits. These are usually marked with a black and white shield-shaped sign.

In 1956, the National Interstate of Defense Highways was created under the Federal-Aid Highway Act in order to produce the Interstate network numbering system. One or two digit numbered Interstate highways are known as primary Interstates and major interstates. Interstate routes are numbered by multiples of five and extend across most of the country such as I-5 or I-95.

Routes of three digits are connected to a two digit highway that designates a city. The numbering for the three digit route comes from the major Interstate of two digits. An example of this is how I-880 forms a junction with I-80 in Oakland. The first digit represents the purpose of the highway. An odd number will lead to a city and an even number will go around the city.

State or Provincial Highways are routes that follow the numbering system for highways in states such as California. Though significantly shorter than their Federal and Interstate counterparts, they share the same odd/even numbering scheme as the US Highway system. Smaller and single digit numbers are most often reserved for main roads and local city areas. Numbers are divided by Northern and Southern locations, with each grouped by twos. For example, California State routes 22 and 23 are in Northern California, while 24 and 25 are in the south. Route 1 travels across the state from north to south. California State Highway signs initially displayed a black and white sign with a bear taken from the state flag. The design was changed in 1959 and the bear removed. Today's sign designs still display the same "minor's spade" shape, but are now green.

Route numbers for State or Provincial Highways correlate with County route schemes. County routes have a specific numbering system for their road in which the first digit is a letter and the second to third digits are numbers. Dividing the state by Northern and southern, the County numbering system uses the first letters of the alphabet (e.g. A) to identify a northern portion of the state. Higher numbers and letters are indicative of routes located or headed towards southern California. Therefore, an Alameda County road could be designated as Route J2 and Santa Barbara, Route S20.

Confusing? It can be, but the number system allows traffic control and planners to follow an established order that eliminates potential confusion in a complex world filled with highways, byways and roads.

1. Richard F. Weingroff. Federal-Aid Act of 1956: Creating the Interstate System, 2011.
2. Daniel P. Faigin. California Highways, 2013.
3. Hamish Reid. California Driving: Roads Traffic, 2012.
4. Community Manager of AAA Today. Birth of the U.S. Numbered Highway System, 2013.
5. AARoads blog contributor, California "S" County Roads, 2013.

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