California postmile

[1] California was the last state in the country to adopt mile markers, and exit numbers were not implemented until 2002.

[2] The state started the Cal-NExUS program in 2002, which would create a uniform exit numbering system for freeways.

[6] Postmiles on callboxes are approximate due to a convention that all callboxes on the northbound or eastbound side of a divided roadway are assigned even numbers while all those on the southbound or westbound side are assigned odd numbers, even though the call boxes are often located directly across from one another.

Alphabetic prefixes on postmile markers and bridges differ from callbox prefixes because the callbox system is maintained by each county, while Caltrans maintains postmile markers and bridge signs.

Listed in miles, postmile values usually increase from south to north or west to east depending upon the general direction the route follows within the state.

Like California, these two states record mileages through individual counties in their respective route logs.

Also, all non-Interstates in Illinois and Kentucky have markers showing mileage from the western or southern border of the county.