Why did California choose not to number its freeway interchange exits in the past?
The California system for identifying precise locations on highways was developed and put in place many years before the federal system of numbering exits was created in concert with the building of the interstate highway system in the 1950s. The California system uses post miles that begin and end at county lines, rather than at a state border. The use of exit numbers became a federal requirement in 1971. By that time, California had already built more than 90 percent of the highway system we still use today. The federal government allowed California to continue using its system citing the additional cost to the state to make the conversion. All of California’s traffic and accident information is based on the existing county-specific post mile system in use in the state.
