Factoids: Highway Route Numbers

Have you ever wondered how freeways are numbered? Believe it or not, there is a system for numbering highways and freeways! First off, to provide a visual perspective, here is a map of the San Francisco Bay Area.

San Francisco Bay Area Freeway System

State Highways

California State Routes are designated with the this symbol. As a general rule, odd numbered routes are generally south to north, while even numbered routes are generally east to west.

Business Routes

Business routes are generally local streets or roads in a city or urban area that provides guidance for the traveling public to leave the main highway, patronize local businesses, and continue on to rejoin the main route at the opposite end of the city or urban area.

The Interstate System

Numbering conventions for the interstate system are as follows: routes with one or two-digit numbers are north-south or east-west through routes.  Routes with three-digit numbers, where the first number is odd, are interstate spur routes (routes that branch off from the main freeway). Routes with three-digit numbers, the first of which is even, are loops through or belt routes around cities.

Ever wonder why most of the freeways in and around the Bay Area have the number “80” in them? Well that is because spur routes and loops through or belt routes are numbered after the through route that they branch off of. For example, Interstate 80 is the through route, while interstates 880, 280, and 680 are belt routes around the city. Interstate 580, and 780  are spur routes associated with the through route, interstate 80.

Greater Los Angeles Area

The same nomenclature rules hold true in the Los Angeles region. Interstates 10 and 5 are the major through routes that go through the area with respective spur routes (110, 710, 105, ) and belt routes (210, 405, and 605).


1 Comment

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One response to “Factoids: Highway Route Numbers

  1. I like this article! Very informative.. and it explains why there are so many 80’s in the bay area, I’ve always been curious about that

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