List of auxiliary Interstate Highways

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).

Dwight D. Eisenhower National System of Interstate and Defense Highways
Highway shield for Interstate 295
Interstate Highways in the 48 contiguous states
System information
Formed	June 29, 1956[1]
Highway names
Interstates	Interstate X (I-X)
System links
Interstate Highway System Main Auxiliary Suffixed Business Future

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.

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-115 contains an odd number in the first digit (1), which indicates that this freeway is a spur. The last two digits signify the highway's origin. In this case, the "15" in I-115 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 that does not currently meet Interstate Standards but it may be upgraded later on. An example is I-369 in Texas, which currently does not connect with parent route I-69.
• It may connect two unrelated Interstate highways, like I-390 in New York State and I-355 in Illinois.
  • States differ on their interpretation of the numbering convention when an Interstate behaves in this case In the I-390 example above, the route is assigned odd first digit. The I-275 in Tennessee, a connector between I-40 and I-75, 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:

• I-110 in California links I-10 with the Port of Los Angeles. This freeway was built before the creation of the Interstate Highway System as the Harbor Freeway, and was later adopted into the Interstate Highway System.
• I-180 in North-Central Pennsylvania connects Williamsport and Lycoming County with I-80 in Milton, but does not actually enter Lycoming County. I-180 also serves as a connection to those traveling to New York and I-86 via U.S. Route 15 and the Future I-99 Corridor at its western terminus.
• I-190 in New York connects the cities of Niagara Falls and Buffalo with I-90.

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:

• I-380, located in the San Francisco Bay Area of Northern California begins at I-280 and connects with US 101 at San Francisco International Airport.
• I-190 in Massachusetts branches off from I-290 near Worcester.
• I-795 in Baltimore County, Maryland branches off from I-695.

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:

• I-220 in Louisiana serves as a bypass of downtown Shreveport.
• I-440 forms a loop around the south side of Nashville.
• I-890 travels through downtown Schenectady, which I-90 avoids.

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:

• I-275 in Ohio, Kentucky and Indiana encircles the city of Cincinnati.
• I-465 in Indiana encircles the city of Indianapolis.
• I-495 in Maryland and Virginia encircles the city of Washington, D.C., and is referred to as "The Capital Beltway".

Note: this table sorts the route numbers by parent highway.

Number	Length (mi)[3]	Length (km)	Southern or western terminus	Northern or eastern terminus	Formed	Removed	Notes
H-201	4.10	6.60	H-1 in Halawa, HI	H-1 in Honolulu, HI	02004-01-012004[4]	current	Signed as Route 78 until 2004
I-105	17.32	27.87	SR 1 in El Segundo, CA	I-605 in Norwalk, CA	01963-01-011963	current	Replaced segments of SR 42
I-205	12.97	20.87	I-580 near Tracy, CA	I-5 near Tracy, CA	01970-01-011970	current
I-305	6.00	9.66	I-80 in West Sacramento, CA	I-80 Bus/US 50/SR 99 in Sacramento, CA	01981-01-011981	current	Unsigned
I-405	72.15	116.11	I-5 in Irvine, CA	I-5 in Mission Hills, CA	01964-01-011964	current
I-505	32.98	53.08	I-80 in Vacaville, CA	I-5 in Dunnigan, CA	01977-01-011977	current	Originally part of I-5W
I-605	27.40	44.10	I-405 in Seal Beach, CA	I-210 in Irwindale, CA	01964-01-011964	current
I-805	28.02	45.09	I-5 in San Ysidro, CA	I-5 in Sorrento Valley, CA	01959-01-011959	current
I-905	8.96[5]	14.42	I-5 in San Ysidro, CA	Fed. 2 at the United States-Mexico border in Otay Mesa, CA	proposed	—	Currently SR 905, proposed to be signed as an Interstate
I-105	3.49	5.62	OR 99 in Eugene, OR	I-5 in Springfield, OR	01958-01-011958	current
I-305	—	—	Pine Street in Salem, OR	I-5 in Keizer, OR	01957-01-011957	01976-01-011976	Canceled
I-405	3.53	5.68	I-5 in Portland, OR	I-5 in Portland, OR	01958-01-011958	current
I-505	3.17	5.10	US 30 in Portland, OR	I-405 in Portland, OR	01969-01-011969	01979-01-011979	Canceled
I-205	36.64	58.97	I-5 in Tualatin, OR	I-5 in Salmon Creek, WA	01958-01-011958	current
I-405	30.30	48.76	I-5/SR 518 in Tukwila, WA	I-5/SR 525 in Lynnwood, WA	01957-01-011957	current
I-605	—	—	WA 99 in Federal Way, WA	I-5 in Everett, WA	—	—	Never built, was planned to bypass Seattle, WA
I-705	1.50	2.41	I-5/SR 7 in Tacoma, WA	Schuster Parkway in Tacoma	01978-01-011978	current
I-210	4.9	7.9	I-10 in Mobile, AL	I-65 in Prichard, AL	—	—	Currently I-165, the route number was decommissioned because it had no connection to I-10
I-410	—	—	I-10/I-17 in Phoenix, AZ	I-10 in Phoenix, AZ	—	—	Now part of I-10 in Phoenix, AZ
I-510	—	—	I-10/SR 51 in Phoenix, AZ	SR 101 in Phoenix, AZ	—	—	Currently designated as SR 51 (Piestewa Freeway)
I-710	—	—	I-10 in Tucson, AZ	North Campbell Avenue/East 6th Street in Tucson, AZ	—	—	Mostly never built freeway that was to connect to University of Arizona campus from I-10
I-110	20.43	32.88	SR 47 in San Pedro, CA	I-10/SR 110 in Los Angeles, CA	01978-01-011978	current	Originally part of US 6, then signed as SR 11
I-210	48.72	78.41	I-5 in Sylmar, CA	SR 57/SR 210 in Glendora, CA	01964-01-011964	current	Does not connect physically with I-10 as segment from SR 57 east to I-10 is still signed as SR 210, formerly SR 30 prior to 2007.
I-710	19.66	31.64	Terminal Island in Long Beach, CA	Valley Boulevard in Alhambra, CA	01983-01-011983	current	Originally signed as SR 7
I-110	6.94	11.17	US 98 Bus. near Pensacola, FL	I-10 near Pensacola, FL	01969-01-011969	current
I-110	8.89	14.31	I-10 in Baton Rouge, LA	US 61 in Baton Rouge, LA	01964-01-011964	current
I-210	12.40	19.96	I-10 west of Lake Charles, LA	I-10 east of Lake Charles, LA	01964-01-011964	current
I-310	11.25	18.11	US 90/LA 3127 in Boutte, LA	I-10 west of Kenner, LA	01983-01-011983	current
I-310	2.70	4.35	US 90 Bus. in New Orleans, LA	I-10 in New Orleans, LA	01964-01-011964	01969-01-011969	Canceled Vieux Carré Riverfront Expressway
I-410	1.90	3.06	LA 67 in Baton Rouge, LA	I-10 in Baton Rouge, LA	01961-01-011961	01964-01-011964	Renumbered as I-110
I-410	48.5	78.1	I-10 west of New Orleans, LA	I-10 in New Orleans, LA	01969-01-011969	01977-01-011977	Canceled southern bypass of New Orleans; completed portions became I-310 and I-510
I-510	3.04	4.89	LA 47 in New Orleans, LA	I-10/LA 47 in New Orleans, LA	01992-01-011992	current
I-610	4.52	7.27	I-10 at Metairie–New Orleans, LA line	I-10 in New Orleans, LA	01965-01-011965	current
I-910	9.70	15.61	US 90 Bus. in Marrero, LA	I-10/US 90 Bus. in New Orleans, LA	01999-01-011999	current	Unsigned; completely concurrent with US 90 Bus.; both designation are temporary placeholders for Future I-49
I-110	4.10	6.60	US 90 in Biloxi, MS	I-10 in D'Iberville, MS	01988-01-011988	current
I-310	—	—	US 90 near the Port of Gulfport, MS	I-10 in Gulfport, MS	proposed	—	Future spur into Gulfport, MS
I-110	0.92	1.48	Av Abraham Lincoln at the United States-Mexico border in El Paso, TX	I-10 in El Paso, TX	01967-01-011967	current
I-410	49.49	79.65	Beltway around San Antonio, TX		01959-01-011959	current
I-610	37.97	61.11	Beltway around Houston, TX		01975-01-011975	current
I-215	54.50	87.71	I-15 in Murrieta, CA	I-15 in Devore, CA	01982-01-011982	current	Originally signed as I-15E, then SR 215
I-115	1.19	1.92	I-15/I-90 in Butte, MT	Iron Street in Butte, MT	01971-01-011971	current
I-315	0.83	1.34	I-15 in Great Falls, MT	I-15 Bus/US 89 in Great Falls, MT	01960-09-191960	current	Unsigned
I-215	11.10	17.86	I-15/Clark County Route 215 in Enterprise, NV	I-11/US 93/SR 564 in Henderson, NV	01996-01-011996	current
I-515	20.54	33.06	US 93/US 95 in Henderson, NV	I-15/US 93/US 95 in Las Vegas, NV	01976-01-011976	02024-01-012024	Not signed until 1994, this route is entirely concurrent with US 93/US 95; replaced by northward extensions of I-11 in 2017 and 2024
I-215	29.02	46.70	I-80 in Salt Lake City, UT	I-15 in North Salt Lake, UT	01963-01-011963	current
I-415	2.39	3.85	I-80 in Salt Lake City, UT	4430 S in Holladay, UT	01965-01-011965	01969-01-011969	Designation was scrapped to provide a single route number 215 for the entire route.
I-516	6.49	10.44	SR 21/SR 204 in Savannah, GA	SR 21 in Garden City, GA	01985-01-011985	current
I-420	5.40	8.69	I-285 in College Park, GA	I-20 in Atlanta, GA	01983-01-011983	01986-01-011986	Never built, was planned to bypass Atlanta, GA
I-520	23.34	37.56	I-20 in Augusta, GA	I-20 in North Augusta, SC	01980-01-011980	current
I-220	17.62	28.36	I-20/LA 3132 in Shreveport, LA	I-20 in Bossier City, LA	01979-01-011979	current
I-420	10.20	16.42	I-20 in West Monroe, LA	I-20 in Monroe, LA	01957-01-011957	01964-01-011964	Canceled bypass of Monroe
I-220	12.01	19.33	I-20 in Jackson, MS	I-55 in Ridgeland, MS	01981-01-011981	current
I-820	35.17	56.60	I-20 in Fort Worth, TX	I-20/US 287 in Fort Worth, TX	01959-01-011959	current
I-222	—	—	I-22 in Graysville, AL	I-422 in Brookside, AL	proposed	—	Proposed connector between I-422 and I-22 due to the inability to make a direct connection between the two routes.
I-422	—	—	I-20/I-59/I-459/US 11 in Bessemer, AL	I-59 in Argo, AL	proposed	—	Currently under construction; will only be indirectly connected to I-22 via I-222.
I-124	1.97	3.17	I-24 in Chattanooga, TN	US 27 in Chattanooga, TN	01960-01-011960	current	Unsigned
I-225	12.00	19.31	I-25 in Denver, CO	I-70 in Aurora, CO	01976-01-011976	current
I-425	5.31	8.55	I-25/US 36 at Welby, CO	I-70/US 36 at Denver, CO	—	01959-01-011959	Renumbered as I-270 by AASHTO
I-126	3.68	5.92	I-26 in Columbia, SC	US 21/US 76/US 176/US 321 in Columbia, SC	01961-01-011961	current
I-326	5.24	8.43	I-26 in Cayce, SC	SC 48 in Columbia, SC	01976-01-011976	01995-01-011995	Now part of I-77, formerly unsigned
I-526	19.26	31.00	US 17 in Charleston, SC	I-526 Bus./US 17 in Mount Pleasant, SC	01989-01-011989	current
I-129	3.48	5.60	US 20/US 75/US 77 in South Sioux City, NE	I-29/US 20/US 75 in Sioux City, IA	01976-01-011976	current
I-229	14.97	24.09	I-29 in St. Joseph, MO	I-29/US 59/US 71 in St. Joseph, MO	01986-01-011986	current
I-229	11.33	18.23	I-29 in Sioux Falls, SD	I-90 near Sioux Falls, SD	01966-01-011966	current
I-130	5	8.0	I-30/I-49 in Texarkana, AR	US 59/US 71 near Texarkana, AR	02000-01-012000	02014-01-012014	Was given a future designation during its existence due to not being upgraded to Interstate Highway standards; freeway became part of I-49 once completed
I-430	12.93	20.81	I-30/US 67 in Little Rock, AR	I-40/US 65 in Little Rock, AR	01980-01-011980	current
I-530	46.65	75.08	US 65 in Pine Bluff, AR	I-30/I-440 in Little Rock, AR	01999-01-011999	current
I-630	7.40	11.91	I-430 near Little Rock, AR	I-30 in Little Rock, AR	01985-01-011985	current
I-235	13.78	22.18	I-35/I-80 in West Des Moines, IA	I-35/I-80 near Des Moines, IA	01961-01-011961	current
I-135	95.74	154.08	Kansas Turnpike/I-35 in Wichita, KS	I-70/US 81 in Salina, KS	01976-01-011976	current
I-235	16.52	26.59	I-135/US 81 in Wichita, KS	I-135/US 81/K-15/K-254 in Wichita, KS	01965-01-011965	current
I-335	50.13	80.68	I-35/Kansas Turnpike/US 50 in Emporia, KS	I-470/Kansas Turnpike in Topeka, KS	01987-01-011987	current
I-435	80.81	130.05	Beltway around Kansas City, KS, and Kansas City, MO		01965-01-011965	current
I-635	8.90	14.32	I-35 in Overland Park, KS	I-29/US 71 in Kansas City, MO	01968-01-011968	current
I-335	2.74[6]	4.41	I-94 in Minneapolis, MN	I-35W in Minneapolis, MN	01964-01-011964	01978-01-011978	Canceled
I-535	2.78	4.47	I-35/US 53 in Duluth, MN	US 53/WIS 35 in Superior, WI	01971-01-011971	current
I-235	5.36	8.63	I-35/I-40 in Oklahoma City, OK	I-44 in Oklahoma City, OK	01989-01-011989	current
I-335	19.6	31.5	SE 89th Street in Oklahoma City, OK	I-44 in Luther, OK	02024-01-012024	current	Routed along the Kickapoo Turnpike[7]
I-635	37.00	59.55	SH 121 in Grapevine, TX	I-20 in Balch Springs, TX	01959-01-011959	current
I-440	9.96	16.03	I-30/I-530 near Little Rock, AR	I-40/AR 440 near Little Rock, AR	02003-01-012003	current
I-540	15.87	25.54	US 271/AR 253 near Fort Smith, AR	I-40 in Van Buren, AR	01965-01-011965	current
I-140	25.4	40.9	US 17 near Winnabow, NC	I-40/US 17 in Wilmington, NC	02008-01-012008	current
I-240	9.54	15.35	I-26/I-40/US 74 near Asheville, NC	I-40/US 74A in Asheville, NC	01980-01-011980	current
I-440	16.77	26.99	I-40/US 1/US 64 near Cary, NC	I-40 near Raleigh, NC	01991-01-011991	current
I-540	25.84	41.59	I-40 near Durham, NC	I-87/US 64/US 264 near Knightdale, NC	01997-01-011997	current
I-840	21.9	35.2	I-40/I-73/US 421 in Greensboro, NC	I-40/I-85/I-785/I-85 Bus. in Greensboro, NC	02011-01-012011	current
I-240	16.22	26.10	I-44/US 62 in Oklahoma City, OK	I-40/US 270 in Oklahoma City, OK	01965-01-011965	current
I-440	9.96	16.03	I-40/I-240 near Oklahoma City, OK	I-35 in Oklahoma City, OK	—	01975-01-011975	Now part of I-44
I-140	11.17	17.98	I-40 near Farragut, TN	US 129 near Alcoa, TN	01987-01-011987	current
I-240	19.27	31.01	I-40 in Memphis, TN	I-40 in Memphis, TN	01970-01-011970	current
I-440	7.64	12.30	I-40 in Nashville, TN	I-24 in Nashville, TN	01987-01-011987	current
I-640	7.03	11.31	I-40 in Knoxville, TN	I-40 in Knoxville, TN	01982-01-011982	current