California Numbered Exit Uniform System

Exit numbers in the United States are assigned to freeway junctions, and are usually numbered as exits from freeways. Exit numbers generally are found above the destinations and route number(s) at the exit, as well as a sign in the gore. Exit numbers typically reset at political borders such as state lines. Some major streets also use exit numbers. Freeway exits in the United States are usually numbered in two formats: distance-based and sequential.

Interstate Highways

The Federal Highway Administration (FHWA) generally requires exit numbers (mile-based or sequential) on the Interstate Highway System; the FHWA established that requirement in 1970. The ''Manual on Uniform Traffic Control Devices'' (MUTCD) encouraged use of mileposts and exit numbering by 1961. The MUTCD mandated exit numbering in 1971. The FHWA granted California an exception due to the cost of installing and maintaining additional signage; the state was able to obtain a waiver because it had already built most of its freeways, although some freeways in Los Angeles County received junction numbers: Interstate 10 (I-10) was the only freeway in the county that had a complete set of junction numbers. I-5, US Route 101 (US 101), and then State Route 11 (now I-110/SR 110) were numbered for short distances from downtown Los Angeles. Freeway connections were unnumbered, and junction numbers were only shown on plates, not on gore signs. In 2002, the Cal-NExUS program began to completely number California's junctions. The program is not well-funded, especially because of California's budget woes, so exits are only being signed with numbers when signs need to be replaced. As the efficiency of an exit numbering system for navigational purposes depends on all exits being consistently numbered, the usefulness of the system while only some exits are numbered is limited. Originally, the initial completion date for this project was set as November 2004. The deadline was then extended to 2008. However, the 2006 edition of the '' California Manual on Uniform Traffic Control Devices'' removed any sort of compliance deadline for the exit numbers.

, nine states—mostly in the Northeast—and the District of Columbia used sequential numbering schemes on at least one highway, although the 2009 edition of the MUTCD requires these jurisdictions to transition to distance-based numbering. Although a ten-year compliance period was proposed for the new edition of the MUTCD, a compliance date for this change was ultimately not adopted with the 2009 edition, meaning that the transition is accomplished through a systematic upgrading of existing signing and there is no specific date by which the change must be implemented. However, the FHWA has required that all federally funded routes with sequential numbering eventually be converted to mileage-based exit numbers. To that end, the FHWA has required each state that currently uses sequential exit numbering to submit a plan to eventually transition to distance-based exit numbers. Some of the states that currently have sequential numbering either have or intend to request a waiver from the Federal Highway Administration to retain their current numbering systems, while others have planned a gradual transition to mileage-based exit numbering over time as existing signage reaches the end of its serviceable life and is replaced.

The mile-based requirement mandates multiple exits in the same mile to use a letter suffix in alphabetical order. This also applies to divided interchanges, where two exits are used for opposite directions of the road, for example on full cloverleaf interchanges. Older exit numbering schemes sometimes use cardinal directions (E, N, S, W, often E-W or N-S) depending on the directionality of the cross route(s), for example I-93 in New Hampshire uses exits 15E and 15W for the cloverleaf interchange with US 202 in Concord which is signed east and west at the interchange. Many exits in the Northeastern states which currently or formerly used sequential numbering schemes had these directional abbreviations, but most have converted to A-B schemes. (, New Hampshire is the only state to have never used distance-based exits, including experimental dual exit/mile numbers/letters.)

The New Jersey Turnpike mainline splits into an Eastern Spur and Western Spur between interchanges 15 and 18. Because of this, E and W suffixes are present on these spurs (15E-16E-18E and 15W-16W-18W) to differentiate the interchange and roadway. One interchange on the Eastern Spur was constructed at a later time between 15E and 16E, creating an exit 15X. The letter X was used to represent access to the Secaucus Junction rail station (in the planning stages as Secaucus Transfer, or Xfer), and to avoid an Interchange 15EA designation.

Several states still maintain systems other than the MUTCD-standard mileage based systems, among these are:

* Alaska: Exits on freeway portions of Alaska's Interstate Highways are currently unnumbered.
* Connecticut: Sequential, except for I-395 and I-691. Other interstates will be converted to mile-based exit numbers by 2029. Connecticut planned to convert I-91 to mileage-based exit numbering in 1974, however, ConnDOT abandoned that initiative due to objections from local businesses.
* Delaware: Exit numbers are sequential on I-95 and I-495. I-295 has no exit numbers at all, however, DelDOT has made a reference on a 2016 construction notice referring to the exit to I-495 north as exit 2.
* District of Columbia: Historically, the only exit numbers posted in the District consisted of sequential numbers on I-295. The other freeways within the District of Columbia did not have exit numbers, but in 2008 the District began posting sequential numbers on I-395. , not all interchanges had received numbers. The close proximity of the interchanges on this short freeway, coupled with the lack of space for new interchanges, renders the sequential system more practical than the mileage-based.
* Maine: The first nine exits on I-295 through Portland and South Portland, as well as I-395 thru Bangor and Brewer are sequentially numbered.
* Massachusetts: Mileage based. I-291 and I-391 near Springfield, along with the Lowell Connector in Lowell, and Route 213 in Methuen are sequentially numbered. However, those roadways are short and have exits that are generally spaced in one-mile increments, closely matching the existing mile markers. The Lowell Connector does not have any mile markers currently posted along the roadway.
* Mississippi: Exits on I-69 are unnumbered.
* New Hampshire: All sequential. New Hampshire DOT has reportedly received permission to use federal funding to convert to mileage-based, but has yet to announce a formal plan for conversion. The New Hampshire General Court has considered legislation authorizing and directing the conversion to mile-based exit numbers, but former Governor Chris Sununu repeatedly stated his opposition to eliminating New Hampshire's existing sequential exit numbering system.
* New Jersey: Mileage-based with the exception of I-676, I-278, and the New Jersey Turnpike (part of which is concurrent with I-95), which are sequential.
* New York: Mostly sequential; exceptions include I-781 (Fort Drum spur), I-890 in Schenectady, I-99, Hutchinson River Parkway, Taconic State Parkway and I-84. I-95 mostly uses sequential numbering, however, exit numbers in The Bronx are mile-based. The mainline of the New York State Thruway utilizes a separate exit-numbering scheme separate from its Interstates; non-Thruway sections of I-87 and I-90 each use three independent (currently sequential) exit-numbering schemes.
* Pennsylvania: Interstates are numbered by milepost with the exception of I-579 and I-676; both are short urban freeways with no exit numbers at all.
* Rhode Island: Rhode Island experimented with dual exit/mile tabs in the 1970s. The state was denied a waiver from the FHWA to retain its sequential numbering system. The state completed renumbering all exit numbers from sequential to mile-based on November 3, 2022, with I-95 being the last interstate to do so.
*Texas: Exits on completed sections of I-69W, I-169, and I-369 are currently unnumbered.
* Vermont: Sequential, with no plans as of late 2018 to change to mile-based. Governor Phil Scott reached an agreement with the FHWA to use a dual sequential/mile-based exit numbering system starting in 2020. Under the agreement, existing sequential numbers will be retained, and supplemental signs added to each exit sign assembly indicating the mile-based exit number.

Two highways ( I-19 in Arizona and Delaware Route 1 E 1 have metric numbering, because they were constructed during the time when the US was thought to be completely converting to metric. DE 1 has used standard mileposts since 2003 when the metric-based posts were replaced, and several exit numbers (79, 83, 86, 88, 119) do not coincide with either the milemarker nor its kilometer conversion as they are offset by miles from a kilometer-based exit. I-19 currently has all exit numbers and distances in kilometers, but speed limits in miles per hour. The road has received funding for the distances to be changed back to miles, but in response to local opposition against exit number changes, the Arizona Department of Transportation had decided to spend the money on other roads instead.

Other highways

Exit numbering on non-Interstate highways is less consistent. For example, North Carolina uses mileage-based exit numbers on all of its freeways, including interstates.
* Alabama: only on US 78 (future I-22).
* Alaska: the Johansen Expressway has three interchanges with sequential exit numbers.
* In Arizona, many of its non-Interstate freeways utilize exit numbers such as the freeway loops ( SR 101 and SR 202) around Phoenix, US 60 and SR 51.
* In Arkansas, US 67 (Future I-57), Arkansas Highway 549 (AR 549), and US 70 on the Hot Springs bypass are the only non-Interstate freeways to have exit numbers. Currently, I-49 from I-40 in Alma to Bentonville in northwest Arkansas follows the old numbering system off its old designation I-540. The exit numbers and mileage are derived from their distance from where the Fort Smith section of I-540 begins at the Oklahoma state line.
* California uses exit numbers on most of its non-Interstate highways statewide when they are built to freeway standards. The notable exceptions are the Ojai Freeway section of SR 33 in and near Ventura, the westernmost section of SR 37 near Novato, the Westside Parkway section of SR 58 in Bakersfield, all but one of the freeway-style interchanges on SR 152 in central California (an interchange with SR 33 north near Santa Nella is numbered as exit 60), the small freeway section of SR 330 in Highland, and the freeway-style interchanges on the southern segment of US 395 in the southeastern part of California (an interchange in the northern segment of US 395 is numbered as exit 8 for SR 70, measured from the California-Nevada state line where US 395 re-enters California near Cold Springs, Nevada). However, like its Interstate Highways, the state's budget concerns have caused exits on these routes to only be signed with numbers when signs need to be replaced.
** On the expressway section of SR 86 near Thermal, the exit for Airport Boulevard is numbered as exit 16, measured from the start of the old SR 86S (S for "supplemental") at 81st Avenue near Oasis

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