|Q||How are highway numbers assigned?|
Highway numbers are basically assigned when legislative approval is given through the California Transportation Commission. The numbers are determined generally by consensus of several agencies on what numbers are available and the location within the state. Numbers are given in the following manner: If the route is determined to be a west to east route, such as Interstate 80, the number will be an even number. If the route is determined to be a south to north route, such as Interstate 5, the number will be odd. However, there are some rare exceptions to that rule, primarily on routes that were created before the rules were established.
All of this is overseen by the California Transportation Commission and you can get more info by contacting the following web site: http://www.leginfo.ca.gov/calaw.html
At that site, put a check mark in the box for Streets and Highways Codes. Then click search. On that page click on Article 2, California Transportation Commission Section 70-86. There is information in Sections 75, 81 and 82 that gives more information. If you look through many of the other links there is a lot of helpful information.
In short, the answer to this question is not an easy one. You can get a good idea of the process from the links availabe with the info in the Streets and Highway Code.