California uses a postmile highway location marker system on all of its state highways, including U.S. Routes and Interstate Highways. The postmile markers indicate the distance a route travels through individual counties, as opposed to mileposts that indicate the distance traveled through a state. The postmile system is the only route reference system used by the California Department of Transportation (Caltrans). The system was operative by 1966.
California was the last state in the country to adopt mile markers, and exit numbers were not implemented until 2002.California Highways The state started the Cal-NExUS program in 2002, which would create a uniform exit numbering system for freeways.Cal-NexUS. Caltrans. Accessed: 10-24-2009. Included was a pilot program for the placing of mile markers along rural freeways. Currently, three freeway segments are a part of the experimental program: the Route 14 Freeway, the Route 58 Freeway in Kern County, and State Route 180 in Fresno. Caltrans has not decided if the mile marker program will be expanded to all rural freeways.Cal-NexUS FAQ. Caltrans. Accessed: 10-24-2009. Regardless, Caltrans will still use and maintain the postmile system on all freeways.
Official postmile definitions 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. The postmile values increase from the beginning of a route within a county to the next county line. The postmile values start over again at each county line.
Enforcement officers, maintenance forces and others use the postmile markers in the field to locate specific incidents or features with reference to the postmile system.
On some stretches of road, the following prefixes may precede the mileage on a postmile marker:
PrefixDescriptionRRealignmentMRealignment of a prior realignmentNRealignment of M mileageCCommercial lanes paralleling main highwayDDuplication (usually due to a meandering county line)GReposting duplicate PM at end of routeHRealignment of duplicationTTemporary connectionSSpurLOverlap due to correction or change
A postmile may also include a milepost equation.
Format A postmile marker is placed along the state highway. Each marker is stenciled with the route, county, and postmile at that location.
Bridge One of the common formats for postmiles are located on a freeway on bridges over cross streets. According to Caltrans, it displays the name of the bridge, the county and route number, and the postmile. The postmile is often painted onto the piers and/or abutments of bridges and overpasses.
Postmile markers These are the white metal paddle markers placed at one-mile intervals, with additional markers placed at significant features along the highway such as bridges and overpasses, junctions, or culverts. The markers are roughly the same size as a standard milepost used elsewhere, but they are white with black text. These markers also indicate turnouts and cross streets ahead.
Callbox Postmiles are also shown on callboxes. A blue placard is mounted on each of the state's callboxes: the top shows which county the callbox is in, and the bottom shows the 2-letter county abbreviation along with the route number and the location's postmile (in tenths of miles). 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.
County prefixes 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. The following table lists postmile and callbox prefixes by county.
County Bridge Callbox County Bridge Callbox Alameda ALA AL Orange ORA OR Alpine ALP AP Placer PLA PL Amador AMA AM Plumas PLU PM Butte BUT BU Riverside RIV RV Calaveras CAL CV Sacramento SAC SA Colusa COL CO San Benito SBT ST Contra Costa CC CC San Bernardino SBD SB Del Norte DN DN San Diego SD SD El Dorado ED EL San Francisco SF SF Fresno FRE FR San Joaquin SJ SJ Glenn GLE GL San Luis Obispo SLO SL Humboldt HUM HU San Mateo SM SM Imperial IMP IM Santa Barbara SB SR Inyo INY IN Santa Clara SCL SC Kern KER KR Santa Cruz SCR SZ Kings KIN KN Shasta SHA SH Lake LAK LK Sierra SIE SI Lassen LAS LS Siskiyou SIS SK Los Angeles LA LA Solano SOL SO Madera MAD MD Sonoma SON SN Marin MRN MR Stanislaus STA SS Mariposa MPA MP Sutter SUT SU Mendocino MEN MC Tehama TEH TE Merced MER ME Trinity TRI TR Modoc MOD MO Tulare TUL TU Mono MNO MN Tuolumne TUO TM Monterey MON MY Ventura VEN VE Napa NAP NP Yolo YOL YO Nevada NEV NV Yuba YUB YB
Similar reference markers in other jurisdictions Sonoma County uses a postmile system on its county roads, but the numbering usually starts at 10.00 rather than at a zero point.
Los Angeles County uses a postmile system similar to the state’s, but their postmile markers contain a red bar on its topCounty Sign Route 23
The states of Nevada and Ohio use reference markers very similar to California's postmile markers. Like California, these two states record mileages through individual counties in their respective route logs. Ohio's system is nearly identical to California's with its reference markers listing the route number, 3-letter county abbreviation, and mileage through the county. The Nevada system is also similar, utilizing 2-letter county abbreviations. However, Ohio uses standard mileposts in addition to reference markers on freeways, while Nevada uses standard mileposts in conjunction with postmile panels on Interstate highways only.
Also, all non-Interstates in Illinois and Kentucky have markers showing mileage from the western or southern border of the county.
See also
Milestone Reference marker (New York)
References
External links Caltrans Postmile Services