Auxiliary_Interstate_Highway

List of auxiliary Interstate Highways

List of auxiliary Interstate Highways

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Auxiliary Interstate Highways (also called three-digit Interstate Highways) are a subset of highways within the United States' Interstate Highway System. The 323 auxiliary routes generally fall into three types: spur routes, which connect to or intersect the parent route at one end; bypasses, which connect to the parent route at both ends; and beltways, which form a circle that intersects the parent route at two locations. Some routes connect to the parent route at one end but to another route at the other end; some states treat these as spurs while others treat them as bypasses. Like the primary Interstate Highways, auxiliary highways meet Interstate Highway standards (with rare exceptions).

Quick Facts Dwight D. Eisenhower National System of Interstate and Defense Highways, System information ...

The shorter auxiliary routes branch from primary routes; their numbers are based on the parent route's number. All of the supplement routes for Interstate 95 (I-95) are designated with a three-digit number ending in "95": I-x95. With some exceptions, spur routes are numbered with an odd hundreds digit (such as I-395), while bypasses and beltways are numbered with an even hundreds digit (such as I-695). Because longer Interstates may have many such supplemental routes, the numbers can repeat from state to state along their route, but they will not repeat within a state.

There are three states that have no auxiliary Interstate Highways: Alaska, Arizona, and New Mexico. North Dakota has an auxiliary route, but it is unsigned, and Wyoming's does not meet Interstate Highway standards.

Terminology and guidelines

Routes that begin with an even number generally connect to the main highway in two locations, while odd numbers only connect in one location.

Auxiliary Interstates are divided into three types: spur, loop, and bypass routes.

The first digit of the three digits usually signifies whether a route is a bypass, spur, or beltway. The last two digits are derived from the main Interstate Highway. For instance, I-515 contains an odd number in the first digit (5), which indicates that this freeway is a spur. The last two digits signify the highway's origin. In this case, the "15" in I-515 shows that it is a supplement to I-15.

Exceptions to the standard numbering guidelines exist for a number of reasons. In some cases, original routes were changed, extended, or abandoned, leaving discrepancies in the system. In other cases, it may not be possible to use the proper number because the limited set of available numbers has been exhausted, causing a "non-standard" number to be used.

Spur route

A spur route's number usually has an odd number for its first digit.[2] It is usually one of the following:

  • It may serve another section of a city or metropolitan area not served by the main freeway (most often the central business district), terminating at a regular city street/avenue or at a substandard freeway, such as I-185 in Columbus, Georgia.
  • It may represent the first portion of a contemplated extended freeway, one that downgrades to below Interstate standards with plans to upgrade it later on. An example is I-540 in Arkansas.
  • It may connect two unrelated Interstate highways—as I-390 in New York State and I-355 in Illinois do.
    • States differ on their interpretation of the numbering convention in this case. In the I-390 example above, the route has both ends at Interstates, but not at the same Interstate on both ends, and is assigned an odd first digit. Another example is I-275 in Tennessee: it is a connector between I-40 and I-75 (a similar case of having both ends at Interstates but not at the same Interstate) and is assigned an even first digit.
    • This may even vary within the same state. For example, in Michigan, both I-196 and I-696 intersect I-96 at one end and I-94 at the other end.

Examples include:

Sometimes, a three-digit Interstate Highway branches off from another three-digit Interstate Highway. These spurs do not connect directly with their parent highways, but are associated with them via the three-digit highways they do intersect with.

Examples include:

Bypass

A bypass route may traverse around a city, or may run through it with the mainline bypassing. In a typical 3-digit Interstate Highway, bypasses usually have both its two termini junctioned with another Interstate highway. Bypass routes are preceded by an even number in the first digit.[2]

Examples include:

In the case of an auxiliary Interstate highway which has both ends at Interstates but not the same Interstate, some states treat these as bypasses while others treat these as spurs—see Spur route above.

Beltway

A beltway (also known as a loop route) completely surrounds a metropolitan city, and it is often connected with multiple junctions to other routes. Unlike other auxiliary Interstate Highways (and by extension, all primary Interstate Highways), beltways do not have termini; however, they have a place where the highway mileage resets to zero. Beltways are also preceded by an even number in the first digit.[2]

Some examples of beltways include:

Auxiliary Interstates

Note: this table sorts the route numbers by parent highway.
More information Number, Length (mi) ...

See also

Notes

  1. According to the FHWA, I-275 in Michigan is only 29.97 mi (48.23 km) because they do not count the length overlapping I-96.[3] MDOT and most major map publishers do count the overlap.[12][13][14]

References

  1. [1]
    Weingroff, Richard F. (Summer 1996). "Federal-Aid Highway Act of 1956, Creating the Interstate System". Public Roads. 60 (1). Washington, DC: Federal Highway Administration. Retrieved March 16, 2012.
  2. [2]
    DeSimone, Tony (October 31, 2002). "Interstate Route Numbering". Route Log and Finder List. Federal Highway Administration. Retrieved February 3, 2008.
  3. [3]
    Adderly, Kevin (December 31, 2015). "Table 2: Auxiliary Routes of the Dwight D. Eisenhower National System of Interstate and Defense Highways as of December 31, 2015". Route Log and Finder List. Federal Highway Administration. Retrieved February 6, 2016.
  4. [4]
    Special Committee on U.S. Route Numbering (December 8, 1990). "Report of the Special Committee on U.S. Route Numbering to the Executive Committee" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. Archived from the original (PDF) on October 16, 2017.
  5. [5]
    Warring, KS (January 2, 2008). "Interstate 905 Freeway Interchanges" (PDF). California Numbered Exit Uniform System. Sacramento: California Department of Transportation. Retrieved February 5, 2009.
  6. [6]
    Cavanaugh, Patricia (October 2006). "Politics and Freeways: Building the Twin Cities Interstate System". University of Minnesota.
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    Humphrey, Spencer (March 7, 2024). "Multiple OKC-area highways, turnpikes to be designated as interstates in coming month". KFOR-TV. Retrieved March 10, 2024.
  8. [8]
    Tennessee Department of Transportation (October 31, 2003). "TDOT Announces Decision on State Route 840 North" (PDF) (Press release). Tennessee Department of Transportation. Archived from the original (PDF) on November 27, 2007.
  9. [9]
    Federal Highway Administration (October 31, 2002). "Table 2: Auxiliary Routes of the Dwight D. Eisenhower National System of Interstate and Defense Highways as of October 31, 2002". Route Log and Finder List. Federal Highway Administration. Retrieved July 8, 2007.
  10. [10]
    Dozier, Daniel A. (September 5, 2013). "Request for I-69 Designation for I-164 from I-64 to US 41" (PDF). Letter to Richard J. Marquis. Indianapolis: Indiana Department of Transportation. Archived from the original (PDF) on March 4, 2016. Retrieved January 9, 2015 – via American Association of State Highway and Transportation Officials.
  11. [11]
    Highway Information Services Division (December 31, 2013). Highway Location Reference. Maryland State Highway Administration. Retrieved March 2, 2012.
  12. [12]
    Michigan Department of Transportation (2021). Next Generation PR Finder (Map). Michigan Department of Transportation. Retrieved October 11, 2021.
  13. [13]
    Rand McNally (2008). "Michigan: Cities" (Map). The Road Atlas. 1 in≈5 mi. Chicago: Rand McNally. p. 52. Detroit & Vicinity inset. § I3. ISBN 0-528-93981-5. OCLC 226315010.
  14. [14]
    Google (February 24, 2010). "Overview Map of I-275" (Map). Google Maps. Google. Retrieved February 24, 2010.
  15. [15]
    "Ask SAM: Upgrades needed before US 52 can be called I-285". Winston-Salem Journal. January 10, 2014. Retrieved January 10, 2014.
  16. [16]
    "NCDOT: Project U-2826". Archived from the original on October 29, 2011. Retrieved April 17, 2014.
  17. [17]
    "State Seeking Future Interstate Designation for US 264 to Greenville" (Press release). North Carolina Governor's Office. Archived from the original on November 10, 2016. Retrieved November 10, 2016.
  18. [18]
    Borggren, Erica J. (October 6, 2014). "I 490 Illinois Establish" (PDF). Archived from the original (PDF) on March 3, 2016.
  19. [19]
    Special Committee on U.S. Route Numbering (June 25, 1979). "Route Numbering Committee Agenda Showing Action Taken by the Executive Committee" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. p. 501. Retrieved November 13, 2014 – via Wikimedia Commons.
  20. [20]
    Special Committee on U.S. Route Numbering (November 14, 1980). "Route Numbering Committee Agenda" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. p. 519. Retrieved November 13, 2014 – via Wikimedia Commons.
  21. [21]
    DeBonis, Mike (November 28, 2011). "Interstate 695 Reappears in D.C." The Washington Post.
  22. [22]
    Highway Information Services Division (December 31, 2013). Highway Location Reference. Maryland State Highway Administration. Retrieved September 24, 2012.
  23. [23]
    Special Committee on U.S. Route Numbering (September 24, 2017). "Special Committee on U.S. Route Numbering" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. p. 4. Archived from the original (PDF) on June 3, 2019. Retrieved October 21, 2017.
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