List of suffixed Interstate Highways
In the United States, there are currently seven routes in the Interstate Highway System that are signed with letter suffixes to the route number. Interstate 35 (I-35) splits into I-35E and I-35W in the Dallas–Fort Worth metroplex in Texas, and similarly splits into I-35E and I-35W in the Minneapolis–St. Paul area in Minnesota. Other suffixed Interstates include I-69C, I-69E and I-69W in South Texas, and I-480N in Ohio, which is designated as such on mile markers but is otherwise unsigned. The state of Maryland has several unsigned suffixed Interstate designations that are designated by the Maryland State Highway Administration, rather than by the Federal Highway Administration (FHWA).
|Dwight D. Eisenhower National System of Interstate and Defense Highways|
Highway shields for Interstate 35E and Interstate 69C
The 1958 Interstate Highway System plan included many suffixed Interstates.
|Formed||June 29, 1956|
|Interstates||Interstate X (I-X)|
There were once many more suffixed Interstates, as the three-digit Interstates were not designated until after all major routes were assigned numbers, including some short connections and spurs. (A few of the shortest, including I-190 and I-195, were assigned three-digit numbers almost immediately.) Most were not equal splits like on I-35, but had the main route continue through, and often the suffixed route never returned to its parent. In 1980, the American Association of State Highway and Transportation Officials (AASHTO) abolished the majority of suffixes due to confusion, renumbering them as three-digit Interstates. For example, I-15E in California has since become I-215.
|Number||Length (mi)||Length (km)||Southern or western terminus||Northern or eastern terminus||Formed||Removed||Notes|
|I-5W||—||—||I-5 in Tracy, CA||I-5 in Dunnigan, CA||—||—||Replaced by I-580, I-80 and I-505|
|I-5E||—||—||I-5 in Tracy, CA||I-5 in Dunnigan, CA||1958||1982||Replaced by I-5|
|I-15E||—||—||I-15 in Temecula, CA||I-15 in Devore, CA||1973||1982||Renumbered from I-215 in 1973 and back to I-215 in 1982|
|I-15W||—||—||I-15 in Murrieta, CA||I-15 in San Bernardino, CA||1957||—||Became I-15 in 1957|
|I-15W||—||—||I-80N in Rupert, ID||I-15 in Pocatello, ID||1958||1980||Became I-86 in 1980; was also planned as I-82N|
|I-24W||—||—||I-55 in Hayti, MO||I-40 in Jackson, TN||—||1964||Did not connect to I-24; renumbered I-155|
|I-35W||85.20||137.12||I-35 in Hillsboro, TX||I-35 in Denton, TX||1959||current|
|I-35E||96.76||155.72||I-35 in Hillsboro, TX||I-35 in Denton, TX||1959||current|
|I-35W||—||—||I-35 in Wichita, KS||I-70 in Salina, Kansas||—||1976||Renumbered I-135|
|I-35W||41.78||67.24||I-35 in Burnsville, MN||I-35 in Forest Lake, MN||—||—|
|I-35E||39.34||63.31||I-35 in Burnsville, MN||I-35 in Forest Lake, MN||—||—|
|I-59B||—||—||Bypass for I-59 around Birmingham, AL||—||—||Renumbered I-459|
|I-69W||1.43||2.30||Fed. 85D at Mexican border on World Trade International Bridge at Laredo, TX||I-35/US 83/US 59/Loop 20 in Laredo, TX||2014||current|
|I-69C||18.02||29.00||I-2/US 83/US 281 in Pharr, TX||US 281/Bus. US 281 near Edinburg, TX||2013||current|
|I-69E||53.31||85.79||East Rio Grande Valley segment: US 77/US 83/University Boulevard in Brownsville, TX
Corpus Christi area segment: US 77/SH 44 in Robstown, TX
|East Rio Grande Valley segment: US 77/Bus. US 77 near Raymondville, TX
Corpus Christi area segment: I-37/US 77 in Corpus Christi, TX
|I-70S||—||—||I-70 in Washington, PA||I-70/I-80S in New Stanton, PA||1958||1964||Became part of I-70 and former I-70 became parts of I-79 and I-76|
|I-70N||—||—||I-70 in Frederick, MD||I-83/I-95 in Baltimore, MD||1958||1973||Became I-70|
|I-70S||—||—||I-70 in Frederick, MD||I-66/I-95 in Washington, DC||1958||1973||Became I-270|
|I-75E||—||—||Bypass for I-75 around Tampa-St. Petersburg, FL||—||1973||Renumbered I-275; later swapped with I-75 in 1973|
|I-80N||—||—||I-5 in Portland, OR||I-80 in Echo, UT||1958||1980||Became I-84|
|I-80S||—||—||I-25/I-70 in Denver, CO||I-80 in Big Springs, NE||1958||1980||Became I-76|
|I-80N||—||—||I-80 in Neola, IA||I-29 in Loveland, IA||—||1973||Became part of I-680|
|I-80N||—||—||I-80/I-90 in Lorain County, OH||I-80S/SR 5 in Braceville Township, OH||1960||1962||Redesignated as I-80|
|I-80S||—||—||I-80 in Youngstown, OH||I-295 in Camden, NJ||—||1970||Extended west to Lodi, OH, by 1962 over former I-80; east end truncated to Monroeville, PA, and the part east of Monroeville renumbered I-76 in 1964; the rest became part of I-76|
|I-81S||—||—||I-81 in Scranton, PA||I-80 in Crescent Lake, PA||—||1964||Formerly I-82, became I-81E (now I-380)|
|I-81E||—||—||I-81 in Scranton, PA||I-80 in Scotrun, PA||1964||1973||Formerly I-81S, became I-380|
|I-82S||—||—||Burley, ID||Tremonton, UT||1957||—||Became I-84|
|I-82N||—||—||Burley, ID||Pocatello, ID||1957||—||Became I-86|
|I-90N||—||—||Buffalo, NY||Canadian border at Lewiston, NY||1957||1959||Original designation for I-190 in New York, renamed I-190|
|I-94N||—||—||Muskegon, MI||I-94 in Grand Rapids, MI||1957||1959||Became I-196 in 1959 and then I-96 in 1964|
|I-180N||—||—||I-80N||Boise, ID||—||1980||This was the only suffixed three-digit Interstate (until I-480N in Ohio was designated); all other spurs of suffixed routes had no suffix; became I-184|
|I-270 Spur||2.10||3.38||I-270 in Bethesda, MD||I-495 in Bethesda, MD||1975||current||Signed as I-270 Spur; designated internally by MDSHA as I-270Y.|
|I-480N||1.99||3.20||I-480 in Maple Heights, OH||US 422 in Warrensville Heights, OH||1974||current||Signed as I-480 on guide signs and reassurance markers, signed as I-480N on mile markers|
|I-495X||1.50||2.41||I-495 in Bethesda, MD||Clara Barton Parkway in Cabin John, MD||1965||current||Also known as Cabin John Parkway; designated internally by MDSHA as I-495X; unsigned; trucks are not allowed on the length of the freeway|
|I-895A||0.71||1.14||I-895B in Brooklyn Park, MD||I-97 in Ferndale, MD||1965||current||Unsigned. Internally designated by MDSHA as I-895A|
|I-895B||2.67||4.30||I-895 in Brooklyn Park, MD||Governor Ritchie Highway in Glen Burnie, MD||1965||current||Unsigned. Internally designated by MDSHA as I-895B|
- Weingroff, Richard F. (Summer 1996). "Federal-Aid Highway Act of 1956, Creating the Interstate System". Public Roads. Washington, DC: Federal Highway Administration. 60 (1). Retrieved March 16, 2012.
- Kansas Department of Transportation (2009). "1970s". Kansas Celebrates 50 Years of Interstates. Kansas Department of Transportation. Archived from the original on February 12, 2012. Retrieved July 16, 2013.
- "Spring to Bring Debut for Interstate Road Numbering". The Herald-Press. St. Joseph, Michigan. Associated Press. January 8, 1959. p. 5. OCLC 10117184. Retrieved July 11, 2018 – via Newspapers.com.
- "Route Number Changes Slated". Lansing State Journal. December 12, 1963. p. 10. OCLC 61312043. Retrieved September 17, 2017 – via Newspapers.com.
- Highway Information Services Division (December 2013). "Highway Location Reference" (Webpage). Maryland Department of Transportation.
- Office of Technical Services (January 1999). "Technical Services Straight Line Diagram for I-480N" (PDF). Ohio Department of Transportation.
- Kirby, J.P.; et al. "Frequently Asked Questions - What are/where all the suffixed Interstates?". misc.transport.road.