In this episode, we explore numbering systems in state highways. It is the start of a four part miniseries on highway numbers in California. Specifically, this episode explores the rhymes and reason for the assigning of signed route numbers to highways with the state shield. This includes looking at the patterns in those numbers, and how the numbering system stands today after the Great Nenumbering. The subsequent episodes in the miniseries will explore the numbering system of US Highways, the numbering of and the history of California’s Interstates, and the signed county route system.
The episode also explores another numbering system on state highways: Post Miles. As opposed to sequential mileage numbers as is found in other states, California uses a system called post miles that identifies points along a highway using a combination of a county and a mile point from the southern/western county line, possibly with clarifying prefixes or suffixes. We discuss this system is good detail.
Our interview is with Andy Richardson, who retired from Caltrans as a Subject Matter Expert in Geographical Information Systems, Linear Referencing Systems, and Postmiles. Andy worked as a GIS specialist for the State of California since 1988, including Caltrans between 2001 and his retirement in 2021. In his last years at Caltrans, he implemented the Department’s current Linear Referencing System.
For more information and links for further explortion, visit the show page on CARoutebyRoute.

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