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Highway Numbering
Highway Numbering in California

Exit Numbers

[Exit Numbers]Yes, exit numbers have finally come to California. For those of you that have never been to California, let me explain. Caltrans has always used a Post Mile system for maintenance purposes, and used exit names for navigation purposes. The Post Mile system was developed and put in place many years before the federal system of numbering exits was created. More specifically, the post mile system was developed in concert with the building of the interstate highway system in the 1950s; the use of exit numbers became a federal requirement in 1971. Because California had already built more than 90% of the current highway system, the federal government allowed California to continue using the post mile system, citing the additional cost to the state to make the conversion.

In 1971, the Division of Highways conducted a pilot project on 5 different routes in the Los Angeles area to evaluate the benefits of exit numbering. No milepost markers were installed in this project. 313 signs were installed for 141 exits. A few of these signs remain in place on these freeways, but the numbers are slightly different from the current exit number determinations. The study recommended that exit numbering be installed on all freeways in urban areas in the state. However, there were concerns about the costs of adding and maintaining thousands of new signs on the highway system. There was also the question of whether to convert from the postmile system to a milepost system, which would have required changes to numerous databases. For these reasons, no programs to install additional exit numbering and mileposts were conducted.

Exit number panels were also developed for the first time in May 1971. The sign code was G70. The G70-2.1 was for exit numbers with 1,2 or 3 digits or letters. The G70-3.1 was for exit numbers with more than 3 digits. Both the 2.1 and 3.1 came in two different sizes, with one size for primary exit signing (meaning G83 and G85 signs) and the other size for secondary exit signing. In July 1971, the sign specs were revised, perhaps to eliminate the different size requirements for primary and secondary signing, which were blanked out. A handwritten note on the sign spec sheets says they became obsolete on January 11, 1972. New sign specs were released that day for the G70-2.2, and the G70-3.2, which replaced version 2.1 and 3.1, respectively. These 1972 versions have a handwritten note that says they were rendered obsolete on June 8, 2001, which is about the time the state began developing the current freeway exit numbering program, and new specs for the G70 were developed. These were released in May 2002. This implied that the G70 remained available for use from 1972 to 2001, although it was not in the Traffic Manual. In research done by Joe Rouse, there was even a 1984 state highway sign chart that included the G70.

In 1999, the California State Senate requested that Caltrans conduct another study regarding the cost of implementing mileposts and exit numbering. In 2001, Caltrans decided to implement an exit numbering program but not place milepost markers. The statewide mileposts and the exit numbering would be determined by calculating the cumulative postmiles of the route. The existing postmile system would remain in place and would continue to be the basis for highway data. The exit numbering system was solely for motorists' benefit.

In 2002, as a result of mandates from Governor Grey Davis and the head of Caltrans (Jeff Morales), Caltrans began installing exit numbers on freeway routes in the state. The estimated cost is upwards of $40,000,000. More than 23,000 signs featuring exit numbers with highly reflective sheeting and lettering will be placed at 5,800 freeway exits on 92 different routes.The first area to be numbered will be near Caltrans Headquarters, and initially, at least one sign has been renumbered per Caltrans district. Route will be numbered beginning with the southernmost and westernmost ends of the route, but exit numbers are used on interchanges on the freeway portions. Numbering should begin at the southernmost/westernmost beginning of the route (legislatively) in the state (unless errors are made or unconstructed and unplanned portions are ignored). The numbers progress from south to north on north-south routes and from west to east on east-west routes. Interchanges spaced less than one mile apart will be assigned a suffix letter (A, B C etc). Note: The new exit number signs (called the Cal-NExUS (California Numbered Exit Uniform System) system) will not replace the post mile system. According to Don Howe, the current maintainer, the term "nexus: in Cal-NExUS also refers to the 58 separate county-specific PM systems that "come together" into one statewide mileage-based system (at least for the counties that have freeways). The rationale behind Mileage based numbering (as opposed to metric) was due to the lack of steam in the metric-initiatives.

Exit number installation began in early 2002 and continues. The initial completion date for this project was set as November 2004. However, budget constraints have slowed the project, and the deadline was been extended. According to a Caltrans spokesman, with the downturn of the California economy in the last few years, funding to do corridor-wide exit number sign projects have been limited to updating signs damaged or in need or replacement of signs with updated EXIT number references using sign maintenance funding. Caltrans is also able to add EXIT numbers when performing rehabilitation projects or new Capital improvements. This limitation has hampered the statewide implementation plans of Districts and has placed some exit number sign update projects on hold at a lower priority to higher priority projects. As a result, a memorandum was signed (dated Oct 17, 2003) by Division of Traffic Operations Deputy Chief, Asif Haq, for Chief Karla Sutliff, that extended the phase-in compliance date for interchange exit numbering to be consistent with FHWA's "Target compliance dates" as outlined in the MUTCD 2003 Introduction pps I-1 thru I-6, see specific dates referenced on I-5 for Section 2E.28 Interchange Exit Numbering to be January 17, 2008. However, the 2006 California MUTCD deletes any compliance deadline.

The official policy is that Interchange numbering shall be used in signing each freeway interchange exit. Each freeway interchange exit will include a minimum of two numbered exit signs: (1) An Advance Guide sign with exit number, and (2) an Exit Gore sign with exit number and arrow or, if not available, an exit number on an adjacent Exit Direction sign at the gore. Where possible, interchange exit numbers are displayed with each Advance Guide sign, Exit Direction sign, and Gore sign on freeways.

Note: Caltrans is following the convention of when a route originates within a State, the southernmost or westernmost terminus shall be the beginning point for exit numbering. Sometimes, the terminus is the end of the constructed or determined portion to the S or W, if there are no plans to ever complete the legislative route. Examples of this are Route 170 and Route 14.

To minimize costs, the new exit number signs will take advantage of existing roadside and overhead signs. Where possible, add-on plates will be used. In some cases, a new sign will be installed. Part of the reason for wholesale replacement is the fact that button copy, which was previously used in California, is no longer manufactured (in other words, the state was stuck: the old way was no longer possible). Evidently, the basic approach will be to place number tabs atop the overhead signs and on advance signs. Ideally, they will go as tabs, but the tabs will, in some cases, be the same width as the sign panels themselves. There appears to be a wide variety of approachs. Some districts include the tab in the sign itself; some use a separately internally drawn box, some use one lines, some use two. Due to new wind loading requirements relating to fatigue (which were in place before the exit number program started), this will require redesign of some of the standard sign trusses. For some signs, if the truss cannot accomodate the extra tab (due to new wind loading requirements), the exit number will be incorporated into the sign itself, superimposed on the upper right corner of the sign panel. In areas where maximum wind loads or existing legends do not permit placement of an add-on plaque or panel, a new sign would be installed. More details are available at https://dot.ca.gov/programs/safety-programs/exit

According to Joe Rouse, Caltrans has changed their sign truss designs in order to meet new wind load standards developed by AASHTO. Caltrans originally placed its exit numbers in the sign panel rather than on top of the truss because the sign trusses that have been in use have not met these wind loading requirements. In 2020, a directive was issued regarding the use of the new sign trusses, and it is specifically noted that the new designs can accomodate exit number tabs. Furthermore, the directive requires that if plans call for an old sign panel to be replaced, the first option should be to use a new truss, but if that is not possible, then the new sign panel cannot exceed the area of the old panel by a certain amount (perhaps 20 square meters). Typically, Caltrans has been installing exit numbers on existing overhead trusses by installing a new sign panel, and the new panel is usually larger than the old one. However, because of this new restriction, Caltrans may be putting really tiny exit numbers on a new panel on an old sign truss, or having an entirely new truss with possibly an exit number tab.

Update: July 2020. At a recent meeting of the California Traffic Control Devices Committee, the California MUTCD was changed. The requirement is now that interchange numbering shall be used in signing each freeway interchange exit, and interchange exit numbers shall be displayed with each Advance Guide sign, Exit Direction sign, and Exit Gore sign. The exit number shall be placed on a separate plaque at above and abutting the top of the Advance Guide or Exit Direction sign. The option to include the exit number tab within the sign has been eliminated.
(Source: Andy Field and Joe Rouse, AARoads Discussion "New exit tabs on CA 57", October 2020)

The following are the guidelines that Caltrans uses when assigning numbers to signs (from Caltrans Policy Directive #TR-0204). The new MUTCD folds these directives into the California supplemental language (blue text with blue line on the page's edge):

  1. California interchange exit numbers follow the Federal Highway Administration (FHWA) Interchange Exit Numbering System of mileage-based reference post numbering as outlined in the latest edition of the Manual on Uniform Traffic Control Devices (MUTCD), Section 2E.28 Interchange Exit Numbering.
  2. Published county/route/postmile and odometer listings within each county provide the basis for continuous mileage-based interchange exit numbers for established California freeway routes. The California Numbered Exit Uniform System (Cal- NExUS) web site, provides a listing of proposed and installed freeway exit numbers indexed by route and direction. The website is updated regularly to reflect when exit number signs are installed at a specific exit. The website listing also includes exit number zone references to rest areas, vista points and weigh stations for information purposes only. These facilities are not considered interchange exits and are not signed with exit numbers. Adjacent interchange exits within the same mile zone of rest areas, vista points, and weigh stations are not assigned suffix letters.
  3. Statewide milepost numbering begins at 0.00, at the southernmost or westernmost terminus of a freeway route in the county of origin. State mileposts continue throughout each route alignment for the duration of the route. If the existing county reference post marker (postmile) is different than the odometer mileage progression, the odometer mileage is used (see exception 3a). There are no interchange exits numbered EXIT 0 (zero). The EXIT 1 zone covers 0.00 to 1.49 miles (rounded to the nearest hundredth of a mile), the EXIT 2 zone covers 1.50 to 2.49, and each exit number zone, thereafter, is one (1.00) mile in length.
  4. A suffix letter A, B, C, D or E is used on multi-exit interchanges, or on multiple interchange exits within the same exit number zone. If used, the suffix letter is displayed with the exit number in a single-line or two-line format. The suffix progression follows a consecutive south to north or west to east progression as the statewide mile post number increases, without any gaps, beginning with the suffix letter “A.” Just as the mileage number decreases in the southerly or westerly directions, the suffix letter begins in the descending direction with the most advanced letter used and descends towards the suffix letter “A” within a given exit number zone without any gaps (example: E, D, C, B, A).
  5. Where two (or more) routes share a common alignment, one route is identified as the dominant route for interchange exit numbering (see order of precedence in #10). State milepost progression increases for all routes, but will only be indicated with exit numbering on the dominant route (see exception 5a).
  6. Interchange exit numbering is determined based on where the centerlines of the freeway route and the intersecting route or city street meet. This can sometimes result in out-of-sequence exit numbers (for example, on Route 210, exits 43, 45, 44). The State Highway Log typically references this county/route/postmile location at interchange locations. Statewide milepost numbering will be continuous, except for the existing breaks in the route that will continue per the postmile orientation of the route, or as estimated on adjoining routes. There are no repeated exit numbers within the same directional route.
  7. No separate exit number signs are identified on specific carpool, or high occupancy vehicle (HOV) facility exits or HOV to HOV system connector ramps. With multiple specific sign packages and pavement markings required for HOV facilities, interchange exit numbering does not apply to these specialty exits and freeway to freeway connectors. This motorist aid system of exit numbering will only apply to mixed-flow lane exits and connectors accessible to trucks and all other freeway users.
  8. Where one or more lanes of traffic diverge from the main line at a single exit, the exit is numbered and signed at the main line diverge as one exit. Generally, there is adequate information displayed on guide signs downstream of the main line diverge to direct a road user to the desired destination, route or street (see exception 8a). Exit numbers are not required for exits from auxiliary lanes, connectors or collector-distributors (see exception 8b).
  9. Freeway routes have the following order of precedence for interchange exit numbering: 1) Interstates, 2) Interstate Business Loops/Spurs, 3) U.S. Highways, 4) California State Routes. Where two routes have the same classification, the lower-numbered route typically has a higher order of precedence.
  10. At an interchange where a freeway route changes to another freeway route, as a road user continues on the mainline, the transition to the route with lesser precedence should be considered a numbered exit and the transition to the route with greater precedence should not be considered a numbered exit.

The document identifies the following exceptions:

As of 2004, Joe Rouse, who at that time was head of the numbering program, provided an update on the installation progress. He noted the following:

<- Numbering of California State Signed Routes -> Post Miles

© 1996-2020 Daniel P. Faigin.
Maintained by: Daniel P. Faigin <webmaster@cahighways.org>.