50 Interstate Oddities

This list was first published on The View From Wisconsin blog in honor of the 50th anniversary of the Interstate Highway System.  It is now published here as the standalone page with the list is offline and it is otherwise available only in the blog post archive.

1. Interstate 97, Maryland. Interstate highways are divided into three general groups: "mainline" Interstate highways, consisting of one or two-digit designations running either north-south (odd numbers) or east-west (even numbers); "bypass" Interstates that circle around a city or a region, with three-digit designations beginning with an even number; and "spur" Interstates that travel from another interstate into a city or downtown area. The longest Interstate is I-90, traveling from Seattle, WA to Boston, MA over 13 states for a total distance of 3,020.54 miles. On the other end of the spectrum is Interstate 97, the shortest mainline Interstate. I-97 travels from I-695 south of Baltimore, past the east side of the Baltimore-Washington International Airport, to US 50/131 just east of Annapolis, for a total of 17.62 miles.
2. Interstate 90, Chicago, IL. The Chicago Skyway is a 7.8 mile toll bridge connecting downtown Chicago with East Chicago, IN. For the longest time, since the "bridge" was opened in 1958, it was considered to be part of I-90 – the longest Interstate highway in the United States. In 1999, however, the city of Chicago discovered in looking through its old records that it was never technically approved as an Interstate highway. Because of this, the city began placing "TO I-90" on all of the reassurance markers on the city-maintained Skyway. However, in 2005 the Federal Highway Administration (FHWA) refuted the mistake, saying that the Skyway has always been part of the Interstate system. The Skyway was "privatized" in 2004, as an international company based in Australia signed a 99-year lease to operate and maintain the toll bridge for the city, under the name Skyway Concession Company, LLC.
3. Interstate 4, Florida. The Interstate Highway System is formally known as the Dwight D. Eisenhower National System of Interstate and Defense Highways. Too many people forget that defense was the reason why the Interstate system was built in the first place; Eisenhower's 1919 convoy of troops and tanks across the US was a primary reason that the government started the program after World War II. It is because of this secondary purpose that not all Interstate highways cross state lines. There are 17 Interstate highways in the continental 48 states that are found in only one state. Interstate 4 is the furthest south of all of them, crossing the middle of the state of Florida from Tampa, through Orlando to Daytona Beach. It is also one of only three single-digit Interstates in the United States; the other two are Interstate 5, which travels from the Mexican border south of San Diego all the way to the Canadian border north of Bellingham, WA, and Interstate 8, which also travels from San Diego east to Casa Grande, AZ and I-10.
4. Interstate 78, New Jersey. The eastern end of I-78 connects Newark International Airport with Manhattan, crossing Newark Bay into Jersey City. However, when the Turnpike Extension ends, I-78 runs across surface streets for several city blocks to the entrance of the Holland Tunnel. I-78's eastern terminus is in the Tribeca District of Manhattan. This is one of a handful of instances of an Interstate having a section of "at-grade" intersections – though it is reasonable to consider that I-78 actually ends at its intersection with NJ 139. Originally, I-78 was intended to cross lower Manhattan into Brooklyn, then up to Queens and into the Bronx where it would end at the I-95/295 interchange. The section crossing lower Manhattan was never built; the section on the other side of the island is now I-278.
5. Interstate 878, Queens NY. As a rule, Interstate highway "spurs" are not very long stretches of freeway. Their intent is to take drivers on a brief stretch of freeway into the downtown portion of a city. Some are so short that they aren't even worth signing as an Interstate – thus creating what is known as a "hidden" Interstate route. An example of this is a section of the Nassau Expressway in New York that connects the Van Wyck Expressway (I-678) and the JFK Expressway (the eastern part of the "loop" around JFK International Airport) is just under three-fourths of a mile. The section is designated as Interstate 878, but is not signed as such over the short route (the rest of the Nassau is signed NY 878). There are a myriad of reasons for the designation; the most logical is that the stretch connects the two parts of the freeway into JFK. There are other "hidden" Interstates, mostly because the stretch of freeway already carries one or more highway designations – such as I-595, which is signed as US 50/301 between I-95/495 outside of Washington, DC to the southern end of I-97 in Annapolis, MD. I-595 is considered to be the longest "hidden" Interstate in the US.
6. Interstate 476, Pennsylvania. Some three-digit interstates are longer than some two-digit "mainline" interstates. One example is I-476, which runs from Chester, PA west of Philadelphia and northwards to I-276 where it becomes the northeast Extension of the PA Turnpike. This section of the Turnpike extends northward to a terminus at Clarks Summit and I-81, just north of Scranton, PA – for a total length of 129.61 miles, the longest three-digit Interstate in the US. I-476 is slightly misnumbered, as it is mostly a north-south route. The original portion of the freeway, from the PA Turnpike down to the Schuylkill Expressway, wasn't finished until the 1990's. The southern portion of the Interstate was finally completed to I-95 in Woodlyn, PA by the Boeing plant along the Delaware River in 1993. Three years later, the Pennsylvania legislature passed a measure to resign the northern extension of the Turnpike as I-476.
7. Interstate 375, Detroit, MI. As pointed out previously, Interstate spurs are generally short freeways that route traffic into a central section of a city or other metropolitan area. Sometimes, the spur is simply a continuation of an existing freeway to a downtown location, after intersecting with another freeway. An example of this would be I-375 in Detroit. I-75, better known as the Chrysler Freeway, swings west once it reaches downtown Detroit, becoming the Fisher Freeway. The Chrysler Freeway doesn't end at that point, though; it continues on to Jefferson Avenue, along Chrysler Drive, ending near the Renaissance Center and the Ambassador Bridge to Windsor, ONT. This short section, signed as I-375, is only 1.06 miles in length – the shortest signed Interstate in the US.
8. Interstate 12, Louisiana. This Interstate is one of the 17 "Intrastate" highways in the US. It is essentially a long 85-mile bypass of I-10, running along the northern edge of Lake Ponchatrain in the Gulf Coast region of Louisiana between Baton Rouge and Slidell, LA. Because a large portion of the twin spans of I-10 across Lake Ponchatrain were damaged in Hurricane Katrina, I-10 was temporarily routed along I-12 until October of 2005, when a two-lane section of the bridge was reopened to traffic.
9. Interstates 35W and 35E, Dallas/Fort Worth. In 1980, the American Association of State Highway and Transportation Officials (AASHTO) declared that Interstate highways should no longer carry a letter designation, and urged state Department of Transportation officials to change existing letter designations to numbers. In the Dallas/Fort Worth Metroplex area, neither city wanted to change the name of their freeway to a three-digit "bypass". So, the two lettered freeways from Hillsboro to Denton, Texas, remain as one of only two left in the US. I-35E is the longer of the two freeways, at 96.76 miles due to its winding route around Waxahachie before entering Dallas.
10. Interstate 16, Georgia. Interstate 16 in Georgia connects Macon, in the middle of the state, to the Atlantic coast city of Savannah. The eastern terminus of the 166.81 mile Interstate is approximately three miles due south of the Georgia/South Carolina border along the Savannah River – making it one of the 17 single-state Interstates. Its western end is at I-75 on the north side of downtown Macon. Like most highways in Georgia, I-16 runs concurrently with GA 404 for its entire length, though the latter is unsigned. The freeway is also named the Jim L. Gillis Highway for its entire length.

11. Interstate 516, Savannah, GA. The W.F. Lynes Parkway on the western edge of Savannah, GA is one of several Interstate highway spurs that travel in both directions from the mainline Interstate – that is, it crosses over the two-digit interstate or intersects and runs concurrently with its parent before traveling off in another direction. The southern spur serves Hunter Army Air Field southwest of Savannah, while the northern spur follows the route of US 80 west to Garden City. The seven-mile-long bypass is somewhat of an oddity, as it contains two 90-degree turns on each side of I-16, making it look like a "Z" on the map. The southern spur connects with the Southwest Bypass, which circles around the west side of Hunter AAF to GA 204. Like other highways in Georgia, I-516 is overlapped by GA 21 for its entire route. US 17 and US 80 join the freeway at exit 3, with US 17 North heading off with I-16 East while US 80 continues on with the Lynes Parkway to exit 7A. US 80 actually runs alongside the last mile of the freeway before heading south and then west, paralleling I-16.
12. Interstates 55, 64 and 70, East Saint Louis, IL. Saint Louis, MO, is considered to be the Gateway to the west by many. It also is a focal point for four Interstate highways that cross or converge on the city. Three of them meet at the south end of the Jefferson National Expansion Memorial (the Gateway Arch), and crosses the Poplar Street Bridge over the Mississippi River to East Saint Louis. This convergence is only one of two instances of three mainline, two-digit Interstate highways sharing the same stretch of road for an extended length. The section extends for just over three miles, until it reaches Interstate 64's eastern section. When a new bridge over the Mississippi is constructed up-river, this alignment may be changed. MoDOT actually claims that I-44 follows the triplex across the Poplar Street Bridge, ending at the state line over the river. This would seem to indicate that the Missouri section of the Poplar Street Bridge is actually a "quadruplet" of four Interstates; however, signage on I-44 eastbound ends at its interchange with I-55 a mile to the southwest.
13. Interstate 170, Saint Louis, MO. Known better to locals as the Inner Belt Expressway, I-170 is one of only three Interstate "spurs" that cross their mainline highway west of the Mississippi River. The heavily-traveled highway runs north to south through the Saint Louis suburbs of Hazelwood, Berkeley, St. John, Overland, University City and Clayton, from Lambert International Airport and I-270 to Interstate 64. The spur was supposed to continue south to I-44 and along River des Peres to I-55 near Bella Villa; the municipalities in south St. Louis County, however, voted the plan down. The freeway right of way was sold off, and a Target store sits right at the end of I-170.
14. Interstate 76 (Colorado to Nebraska, and Ohio to New Jersey). When AASHTO decreed an end to lettered Interstates, it caused some states to renumber sections of freeway to designations already in use in other states. Interstate 76 is such an example; the section from Arvada, CO (northwest of downtown Denver) to I-80 west of Ogallala, NE (I-76 is only in Nebraska for a little over a mile) was changed from I-80S. I-76 was already in use as a freeway designation in the east, having replaced the same I-80S designation from the greater Akron, OH area to the New Jersey Turnpike northeast of Philadelphia, PA. I-76 was actually first designated in the east in 1963 from Camden, NJ to Pittsburgh, PA. I-76 was later routed south into Philadelphia and the Walt Whitman Bridge, ending at I-295 in New Jersey. As the eastern I-76 only touches I-80 once (outside of Youngstown, OH), it would not make much sense for the two routes to be connected via a duplex signing with I-80. The I-76 designation is appropriate for both sections of freeway, as the state of Pennsylvania is well known as being the location of the signing of the Declaration of Independence in 1776, and Colorado became a state in the US Centennial year of 1876.
15. Interstates 35W and 35E, Minneapolis/Saint Paul, MN. This is the only other lettered freeway pair in the US, and it has the same issues as its other pair in Dallas/Fort Worth. The difference here is that it would be relatively easy to re-route I-35 through both cities; I-35 could take the route of I-35W from Applewood into Minneapolis, then multiplex with I-94 east into Saint Paul, then head north on the route of I-35E to Lino Lakes. The remaining sections could be renumbered I-235 and I-435. However, the Twin Cities, like many siblings, do not want to "share" I-35. Unlike its sister Interstate in Texas, I-35W is the longer of the two sections in Minnesota at 41.78 miles, due to its three "step-overs" in downtown Minneapolis.
16. Interstate 394, Minneapolis, MN. When the freeway system was being planned in the Twin Cities in the 1950's, it was decided that US 12 (also known as Wayzata Boulevard) would be turned into a freeway from 3rd Avenue North in Minneapolis out towards St. Louis Park and points west. Originally, only the spur from I-94 east to Washington Avenue in downtown Minneapolis was planned as I-394. The extension to the west and I-494, constructed and opened in the late 1980's, was later added to the route. I-394 was one of the last major Interstates to be completed in the Twin Cities region. The section from I-94 to I-494 is the first route in Minnesota to have a toll "lane"; MNDOT converted reversible high-occupancy vehicle (HOV) lanes into toll lanes requiring a MNPASS transponder for electronic toll collection. The tolls started to be charged in May of 2005. The east spur may become an off-ramp to a new Minnesota Twins ballpark, planned for a parking lot just off the end of the freeway at Washington, near the Target Center.
17. Interstate 180, Hennepin, IL. As you are driving down I-80 through the central plains of Illinois, you come upon a strange freeway interchange: I-180, just east of Princeton, IL. This freeway spur heads south for about 10 miles, takes a hard left and crosses over the Illinois River into Hennepin. There doesn't seem to be any reason for the freeway to exist, until you realize that Interstate highways have a secondary purpose: defense. LTV Steel was a major defense contractor, located in Hennepin – which is why the freeway was built in the 1960's (it opened in 1969). This is the only case of an Interstate highway built for private enterprise in the US. There is a possibility that the freeway could be extended to Peoria on a bypass of IL 29, running alongside the Illinois River, but for now it is a very low-traffic freeway – since LTV Steel went bankrupt in 2002 and the plant was closed.
18. Interstate 84 (Oregon to Utah and Pennsylvania to Massachusetts). This is another case of a lettered Interstate changing numbers. The western section of I-84 was formerly I-80N, traversing from Portland to I-15 in Utah, before re-designation in 1980. I-84 actually violates the AASHTO rules about numerical placement of Interstates, as it intersects with I-82 north just east of Umatilla Army Air Field and Depot in northeast Oregon. The eastern section was already in place between Scranton, PA and the Massachusetts Turnpike. The section of I-84 between Hartford, CT and the Massachusetts Turnpike was originally signed as I-86, and I-84 would have instead diverted along what is now I-384 towards Providence, RI. That section was never built past Bolton, CT.
19. Interstates 90, 94 and 39, central Wisconsin. From the time it opened in 1961, the section of I-90 and I-94 from Wisconsin Dells (later from Tomah) to Madison was the only co-signed Interstate in the state of Wisconsin. In the 1990's, as US 51 was being bypassed to the south in Illinois, a decision was made to do the same to the stretch of US 51 from Portage to Merrill, WI. In 1999, the US 51 freeway in Wisconsin was upgraded to an Interstate designation; since the section in Illinois had already been designated as I-39 (and there was no other number available in the corridor), the section was renumbered as such. A year later, the stretch between Cascade Mountain and the Cherry Valley Interchange in Rockford was re-signed with Interstate 39 signs. This made the 33.5 mile section from Cascade to the Badger Interchange with I-94 east and WI 30 the longest concurrent stretch of three "mainline" Interstates in the US. I-39 and I-43 are slightly out of alignment with the Interstate grid, as they are located east of three higher-numbered freeways (I-45, I-49 and most of I-55).
20. Interstate 43, Wisconsin. Originally the northern spur of the north-south freeway in downtown Milwaukee, I-43 was originally planned to connect downtown Milwaukee (at the current Marquette Interchange) to the unbuilt Belt Freeway, near the Milwaukee-Ozaukee County line. It would have then connected with a northern leg of the Lake Freeway (also unbuilt) that was planned to head north towards Michigan. I-43 was eventually completed near the Lake Michigan shoreline to Sheboygan, Two Rivers and up to Green Bay. Its northern terminus is at US 41 on the northwest side of downtown Green Bay. In 1990, the I-43 designation was placed on the WI 15 Rock Freeway on the southwest side of Milwaukee, extending I-43 to its current length of 191.55 miles to its new terminus at Interstate 90/39 on the east side of Beloit. The I-43 highway continues west into Beloit on WI 81, as the WI 15 designation was reassigned elsewhere in the state (northwest of Appleton). I-43 misses the Illinois border by 2.2 miles on I-39/90. I-43 and I-94 are the only two Interstates that cross, intersect or multiplex with all but one of the other signed Interstates in Wisconsin. The lone Interstate not touched by the pair is I-535, the Blatnik Bridge, in Superior.

21. Interstate 180, Cheyenne, WY. In the 1970's, state officials in Cheyenne wanted to have the capital city served by an interstate highway spur. There was only one problem: the section of highway that would be most logical to have such a spur was already in a built-up area of the city, and officials didn't want to demolish or bypass existing businesses in order to create interchanges. Thus, the city took the funding and simply built two bridges – one over the Union Pacific rail yards, and the other a viaduct over Crow Creek. The Interstate designation was allowed by AASHTO, despite the sub-standard roadway type, since the monies had already been approved for the designation. I-180, which follows US 85, Business I-25 and Business US 87 to Lincolnway, just south of downtown Cheyenne, opened to traffic in 1984. The "interstate" has four stoplights, including its terminus at Lincolnway.
22. Interstate 86 (Idaho and Pennsylvania to New York). For most of the 1980's and 1990's, the only I-86 was the one that ran from Pocatello and I-15 to I-84 in Idaho – the former 63-mile stretch of I-15W. When the section of I-80N from Hartford, CN to the Massachusetts Turnpike was first renumbered, it carried the I-86 designation until it was changed to I-84. In 1999, the New York state route 17 was converted to Interstate I-86 from just outside of Erie, PA to East Corning, NY. The rest of the route, heading east to I-87 and the New York State Thruway, is currently signed "FUTURE 86". The section is not yet completely Interstate standard, as it contains some at-grade intersections in the Horseheads, NY area.
23. Interstate 390, western New York. The New York State Thruway bypasses the lakeshore city of Rochester to the south, so a spur highway was built to connect the Thruway with the city. Originally, NY 47 was a southern bypass around the city, extending from Gates Center on the west to Brighton and east Rochester. The part of the I-390 spur from the Thruway would create an "Outer Loop" connecting the "Inner Loop" (Interstate 490, which was a bypass into the city of Rochester and to an even smaller, two-mile loop in the downtown). However, the routing was not taken well by locals, and the freeway was instead routed to the west to Gates Center. I-390 continues north as NY 390 to the Lake Ontario State Parkway. The southern leg of I-390 was a bypass of old US 15 between the Thruway and Avoca, NY. The 76-mile "spur" connects with I-86 and the Southern Tier Expressway south of Avoca. The freeway is part of a future I-99 corridor, extending south all the way into Pennsylvania.
24. Interstate 238, San Leandro, CA. This freeway is a connector between I-580 (the MacArthur Freeway) and I-880 (the Nimitz Freeway), on the east side of San Francisco Bay. The connector is an extension of the Arthur Breed Freeway, which connects the San Leandro/Oakland area with I-5. CA 238 heads south from the eastern end of I-238 down Mission Boulevard into Freemont, CA – hence the reason for the name of the freeway. However, the section is actually misnumbered, as the I-38 corridor would be somewhere closer to Los Angeles than San Francisco – if there were an Interstate 38. I-238 is the only bypass/spur Interstate without a parent. The state of California chose the 238 designation in 1983 because they had already used up their three-digit Interstate designations for I-80 in the state. It is possible that the stretch could be renumbered I-480, now that the Embarcadero Freeway has been torn down in downtown San Francisco. However, the negative feelings of Bay Area residents towards I-480 (the "world's longest off-ramp," as it was derisively called) may be too much to justify resigning this 2.16 mile stretch of freeway.
25. Interstate 49, Louisiana. Originally running from Shreveport, through the middle of Louisiana to Lafayette and I-10, I-49 was slated to route down and around through the bayou area to the south side of New Orleans. The portion of I-49 under construction south of I-10 was in one of the heaviest-hit parts of Louisiana during Hurricane Katrina; the section is considered to be crucial to a possible future evacuation route from the southern parishes of the state. I-49 is slated to expand northward beyond the state line, connecting north to Kansas City, MO between Shreveport and the Arkansas state line. The plan is to route I-49 north to Texarkana (the existing I-130), Fort Smith, AR (I-540) and Joplin, MO, bypassing US 71 for most of the length. The section between Texarkana and Fort Smith is the most troublesome, as it would require construction through the Ouachita Mountains.
26. Interstate 540, Arkansas. This Interstate connects Bentonville, AR – the home of Wal-Mart stores – with Fort Smith and I-40. Currently, it is one of the few three-digit Interstates to cross over and run concurrently with its "parent" interstate, though it did not begin life that way: initially, I-540 was the spur from Van Buren, AR southwest into Fort Smith, crossing the Arkansas River. Then, in 1995, Arkansas 540 between I-40 at Alma and Mountainburg was opened and re-designated as I-540. Both "spurs" begin their mile marker designation at I-40 with exit 1. The northern extension was opened to Springdale in 1999, then to US 62 west of Rogers in 2000, and then to the north side of Bentonville in 2001. A northern toll road extension is set for completion in 2007-2008 to Bella Vista and the Missouri state line. This tollway will bypass US 71 to the west, entering Missouri near Pineville, with a northern terminus at the existing US 71 freeway in Anderson, MO. When the tollway is completed, it will extend I-540 all the way north to I-44 in Joplin. The entire freeway is planned to become part of the new I-49 corridor, extending south to Texarkana and Shreveport, LA.
27. Interstate 88 (IL and NY). One interstate designation, two states – and no connection in-between. The original section of I-88 was built to connect Binghamton and Schenectady, NY in the 1970's, connecting central New York with the Capitol District. In 1988, the state of Illinois changed the designation of the east-west Tollway (IL 5) from Chicago to US 30 outside of Rock Falls to I-88. The Interstate was later extended west to meet I-80 outside of east Moline (IL 5 continues west into Moline and Rock Island). In 2004, the Tollway was renamed the Ronald Reagan Memorial Tollway, in honor of the late President. Reagan's hometown of Dixon is located near the western end of the Tollway. Both sections of I-88 are single-state Interstates that do not cross a state line.
28. Interstate 526, Charleston area, SC. The state of South Carolina features many interesting locales, such as Hilton Head Island and Myrtle Beach. It also features three separate Interstate spurs that cross over their mainline routes in both directions. The furthest south of these is I-526, which heads off to the west side of Charleston to US 17, and circles around to the east through Hanahan on the Mark Clark Expressway to Mount Pleasant, SC. I-26, meanwhile, spurs into the city of Charleston, ending at US 17 in downtown. The Expressway was approved as an Interstate in 1989. I-526 is planned to continue from its western terminus at US 17 south towards Folly Beach, then east onto James Island and connecting with the SC 30 Freeway (the James Island Expressway). This last stretch of highway would be integrated into I-526, ending the three-quarter loop in downtown Charleston. The proposed west end of I-526 would be about a mile southwest of the eastern terminus of I-26.
29. Interstate 185, Greenville, SC. Originally a spur into downtown Greenville from I-85 northbound – there was no access from southbound I-85 – the freeway ended at the Greenville Medical Center. In 1999, the interchange at I-85 was made full access, while the new Southern Connector toll road was built to the south, creating a bypass of the city by connecting to I-385 in Simpsonville, SC. The new tollway was opened in 2001 as the only Interstate toll road in South Carolina. (The only other toll road is the Cross Island Parkway on Hilton Head Island, extending from US 278 to Palmetto Bay Road on the south end of the island.) Because the tollway was designated to carry the I-185 shield, the "spur" was extended to 17.7 miles in length.
30. Interstate 385, South Carolina. This is the other I-85 spur out of Greenville, SC, connecting the Interstate with I-26 near Clinton, SC on the western edge of the Sumter National Forest. I-385 originally was the northern spur into downtown Greenville, passing Greenville Downtown Airport. The freeway ends six blocks east of US 29; the last six blocks on E. North Street are signed as Business I-385 near the Bi-Lo Center. The freeway was later extended south to connect to US 276, where it now meets I-185 between Mauldin and Simpsonville. The freeway section of US 276 south to Clinton, SC was renumbered I-385 when the northern portion was completed, and US 276 was truncated at I-385. I-385 and I-185 are the two closest Interstate spurs in the US that cross their parent highway.

31. Interstate 95, New Jersey. Interstate 95 is the longest north-south Interstate in the US, traveling through 15 states and Washington, DC from Miami, FL to Houlton, ME. However, if you drive north from Philadelphia into Trenton, NJ, you may be in for a shock. As you circle around to the northeast of Trenton, you come upon the exit for US 1. As you pass the exit, you suddenly see signs informing you that you are now on I-295, heading south to Mercerville. What happened to I-95? It's a simple explanation: NIMBY (Not In My Back Yard). The people of Princeton and New Brunswick, NJ (located northeast of the US 1 exit) did not want to have a freeway running through their county. There were also complaints from the New Jersey Turnpike Authority, which did not want a freeway "bypassing" their turnpike just miles to the south. The freeway was supposed to meet up with I-287 near south Bound Brook; I-95 was then to head east to the Jersey Turnpike near Perth Amboy. Since the project, known as the Somerset Freeway, was killed back in the 1980's, I-95 has had a gap between the New York metro area and Trenton ever since. A new interchange near Newportville, PA will connect the southern leg of I-95 to the eastern extension of the Pennsylvania Turnpike (I-276), which will then route I-95 over to the New Jersey Turnpike and finally "close off" I-95 – sometime around 2010.
32. Interstate 595, Fort Lauderdale, FL. The Everglades Expressway – better known as "Alligator Alley" through the southern edge of Florida – connects the Gulf coast of the state with the greater Miami/Fort Lauderdale area. In the 1960's, this freeway – called the Port Everglades Expressway – was planned to connect Alligator Alley to US Highway 1 in Fort Lauderdale, originally as a toll road. When I-75 was routed south into Miami, the expressway was changed to an Interstate east of the Sawgrass Expressway. By 1989, the entire freeway was opened all the way to the Fort Lauderdale/Hollywood International Airport and US 1. Since the highway was built as a spur from I-95 to the Everglades, the Interstate was given the designation I-595. The section is one of a handful of Interstate spurs that crosses over its parent freeway.
33. Interstate 17, Arizona. This single-state Interstate has an unusual feature: unlike other Interstates that usually begin with a mile marker of 0 or 1, I-17 begins at mile marker 194. The reason for this was the method that the state of Arizona used to reckon mileage. If a route did not enter Arizona from another state, it used the mileage of the route where its southern or western end is located, instead of a zero mile marker. I-17's exit numbers are actually those of the former longer routing of AZ 69, which branched off from US 89 at MM 201, since the two roads were paired together as the Interstate was being completed into Phoenix. AZ 69 now "ends" at I-17 in Cordes Junction. I-17 is one of the most scenic Interstates, traveling 145.76 miles from the Phoenix valley past Piestwa Peak, through the Agua Fria National Monument north to Flagstaff. The landscape is dramatic, going from desert landscape and saguaros to forest and mountains. It is also the gateway to the Grand Canyon area, along US 89 north of Flagstaff. (Personal note: I have driven most of the length of this Interstate. It is very beautiful and scenic.)
34. Interstate 19, Arizona. Because this stretch of single-state Interstate connects Tucson with the Mexican border, I-19's exit numbers (along with distance markers) are signed in kilometers instead of miles. Speed limit signs, however, are still posted in miles per hour. The state decided in 2004, however, that as the signs wear out on the freeway, they will be replaced by mile markers instead. I-19 bypassed old AZ route 89 for its entire 63.35 mile (101.95 km) distance to Nogales. In Nogales, the freeway ends 100 yards north of the Mexican border; about a quarter-mile east at the end of Business I-19 is the beginning of Mexico Federal Highway 15 (M-15). M-15 travels south along the coast of the Gulf of California to Mazatlan and Guadalajara, and then crosses central Mexico to Mexico City (Ciduad de Mexico) – over 1,400 miles, almost 23 times longer than I-19. Not all of M-15 is Interstate grade, however; most of the sections that are freeway-grade are actually toll roads.
35. Interstate 585, Spartanburg, SC. After many years of having I-85 cross about a mile north of Spartanburg, a bypass was built a few miles further north. The old section of I-85 was re-designated as "Business I-85" – but nothing was done about the I-585 spur that took traffic into Spartanburg along the US 176 freeway to US 221 on the north side of the city. To add to an already strange situation, I-585 is signed "early" on US 176 in Spartanburg, with Interstate shields posted several blocks south of the interchange with US 221. Thus, I-585 is an Interstate spur that doesn't extend far enough to its "parent" Interstate in one direction, and extends too far in the other direction. The section of US 176 between the two I-85 legs is being upgraded to freeway status to eventually connect I-585 with I-85 near the campus of USC-Spartanburg.
36. Interstate 27, Texas. This "intrastate" highway connects two of the biggest cities in the Texas Panhandle, Amarillo and Lubbock. The 124.13 mile stretch is one of three single-state mainline freeways in the state of Texas – more than any other state. The freeway's southern terminus is on the far south side of Lubbock, where it meets the southern leg of the TX 289 "loop" around the city. The freeway continues south for about four miles as US 87. I-27's northern terminus is at I-40; the freeway continues north for about a half-mile as US 60, 87 and 287. I-27 follows and is co-signed with US 87 for its entire length. The Interstate is located right in the middle of the Port-to-Plains High Priority Corridor, which could result in its extension all the way south to I-10 and the Mexican border – and, possibly, extended to the north all the way to Denver, CO.
37. Interstate 37, Texas. If the cities of Dallas, TX and Saint Paul, MN could only agree, this could be the number of the Interstate through their cities. Right now, it is a 142-mile connector freeway from San Antonio down to Corpus Christi and the Gulf coast. The southern terminus is the only place in the US where an Interstate, US highway and state highway end at the same place, at the junction of US 181 and TX 35 in downtown Corpus Christi. I-37's northern terminus is at US 281, where it continues to the northern leg of TX Loop 1604. US 281 then continues north as a regular highway into Wichita Falls, missing the Dallas/Fort Worth Metroplex by 20-25 miles to the west. I-37 is unique in that it is one of the only limited-access routes available during a hurricane evacuation situation from the southern Gulf coast of Texas. Because of this, the freeway has crossing gates that allow traffic to travel in "contra-flow" mode – both sides of the freeway traveling in the same direction. I-37 will eventually meet up with a new I-69 near George West at its intersection with US 59.
38. Interstate 45, Texas. This single-state freeway connects the two largest metropolitan areas in the state of Texas – Dallas and Houston. The southern terminus is actually at Galveston, at the interchange of TX 87 and TX Spur 342 on Galveston Island. The freeway services the Johnson Space Center, and then continues north into Dallas. Drivers would be led to believe that the freeway ends at I-30 in Dallas, but in reality the last half-mile before the interchange is signed as US 75, and is actually the unsigned I-345 (or IH-345 in Texas). In an exit numbering anomaly, I-345 continues I-45's exit numbers north to the Woodall Rogers Freeway, where the numbering "restarts" at Exit 1. I-45 is the longest Interstate in the US ending with a 5 that does not travel from border-to-border (at least touch either the Mexican or Canadian border) or cross state lines. It was also the key evacuation route for Hurricane Rita in 2005 – but the length of the highway and heavy flow of traffic turned the freeway into a parking lot, literally. Cars headed north out of the path of the hurricane ran out of gas, and stations along the route ran out of fuel.
39. Interstate 101 (DelMarVa – never built). Delaware's status as the First State does not generally overcome the fact that it is one of the smallest states in the Union. It also has only about 20 miles of Interstate highway within its borders. On top of this, its capital city of Dover is one of only five state capitals not served by an Interstate highway. In addition to Juneau, AK (mentioned elsewhere), the others are: Carson City, NV; Jefferson City, MO; and Pierre, SD. Dover is located the furthest away from the nearest Interstate, at approximately 45 miles south of I-95 in Wilmington. The state of Delaware decided to build a southern extension of the Delaware Turnpike from just south of the Chesapeake and Delaware Canal down the length of the state to Dover AFB outside of the capital. When the extension was completed, state officials petitioned AASHTO to authorize construction of an Interstate 101 that would traverse the rest of the length of the Delaware Peninsula to Salisbury, MD and down the Virginia section of the Peninsula to the Chesapeake Bay Bridge-Tunnel and into Virginia Beach. The request was denied, as AASHTO did not want to authorize a three-digit mainline Interstate. The 165-mile tollway extension remains signed as Delaware Highway 1.
40. Interstate 794, Milwaukee, WI. If you ever have the opportunity to drive from downtown Chicago up Lake Shore Drive to the northern suburbs, consider this while you are driving: this section was actually the southern section of what is now Interstate (and Wisconsin State Highway) 794 in Milwaukee. When planners began mapping out routes for possible Interstates, they intended to supplement the north-south Freeway coming out of downtown Milwaukee with a freeway that would run along the lakeshore and down to the state line, where it would meet a similar freeway coming north from Illinois. This proposal, called the Lake Freeway, would start at the two "ends" and gradually built to meet at or near the state line. Besides Lake Shore Drive and the Edens Expressway, there are two short stretches in North Chicago and Waukegan that were parts of the southern end of the Lake Freeway. The northern end in Milwaukee was proposed in the late 1960's, and was approved by a county-wide referendum in 1974; however, mass opposition to the project caused construction to be stalled. This resulted in downtown Milwaukee having two "stub" freeways, one on the north side of downtown (called the Park Freeway, signed as WI 145) and Interstate 794. I-794 is the section of the East-West Freeway (Interstate 94) located east of its intersection with the North-South Freeway (now known as Interstate 43 at what is now known as the Marquette Interchange) located southwest of downtown Milwaukee. In the 1970's, the section of I-794 east went essentially nowhere. The freeway had two ramps, one heading north and one heading south, both ending in open air to unbuilt freeways. In the early 1980's, the northern ramp was rebuilt to lead to Lincoln Memorial Drive, while the southern ramp was routed to the new Hoan Memorial Bridge over the Port of Milwaukee, terminating at the US Coast Guard Station. It would take many years of political infighting to complete the freeway as far south as Layton Avenue in Cudahy. Because of all the opposition, the "freeway" was downgraded to a limited-access highway, with a traffic signal at the Oklahoma Avenue exit. The signal was necessitated because of the lack of space for a proper off-ramp on the southbound side. WI 794 now ends beyond Layton Avenue on the Far East side of Mitchell Airport at the intersection of Edgerton and Pennsylvania Avenues.

41. Interstate 73, North Carolina. I-73 is currently a single-state Interstate, but it is not planned to remain that way. The existing stretch, extending south along the US 220 freeway from Greensboro to Ulah, NC, is planned to extend south to Charleston, SC and as far north as Sault Ste. Marie, MI. So far, however, most of I-73 is signed as "FUTURE 73" on non-Interstate sections of highway in central North Carolina. I-73 is co-signed with I-74 along its current route; I-74 is another violation of AASHTO guidelines, in that its designation should not be allowed as US 74 runs along the southern edge of the state. In fact, where I-73 and I-74 are currently planned to separate near East Rockingham, I-74 and US 74 would run concurrently on the same stretch of freeway towards Wilmington, NC. There is some debate as to whether I-73 is actually the shortest mainline Interstate in the US, as it is listed at only 12 miles on its own (separate from I-74).
42. Interstate 87, New York. I-87 is a single-state interstate, but it actually does touch a border – the Canadian border between New York and Quebec north of Champlain, NY. The Interstate travels south alongside the Vermont border to Albany as the Adirondack Northway, where it intersects I-90 and the New York State Thruway. I-87 takes over the Thruway's southern leg down past west Point and the US Military Academy. It continues south, missing the New Jersey state line at Suffern, NY by little more than 500 yards at its junction with I-287. I-87 and I-287 duplex all the way to the Hudson River, crossing over the Tappan Zee Bridge and then heading south into the Bronx. In New York City, the freeway is known as the Major Deegan Expressway, from its border with Yonkers to its southern terminus at the Bruckner Expressway and I-278, just north of Randalls Island and the Triborough Bridge. In 1967, Parade magazine declared the Adirondack Northway (or simply "The Northway") to be America's Most Scenic Highway.
43. Interstate 96, Michigan. I-96 was originally a bypass of US 16, heading from Muskegon to Detroit as a single-state Interstate. Its western terminus is US 31, northeast of Muskegon; it traverses the lower peninsula of Michigan, through Grand Rapids and Lansing. In Lansing, it runs for seven miles concurrently with I-69 – the only instance in the US where two Interstates with "reflective" numbers run concurrent with each other. I-96 heads east from the south side of Lansing, past the GM Proving Grounds in Milford to Farmington Hills. It then joins with I-275 south to Livonia, where it heads back east into Detroit on what is now known as the Rosa Parks Memorial Freeway. I-96 ends at the Fisher Freeway, about a mile west of the site of Tiger Stadium in downtown Detroit and two miles northeast of the Ambassador Bridge into Canada.
44. Interstate 465/865, Indianapolis, IN. The "Indianapolis Loop" around the capital city of Indiana has many odd features as it circles around Marion County. First of all, the I-465 freeway crosses, intersects or runs concurrent with four separate freeways (five if you count the I-865 spur to the northwest of Indy). It also runs concurrently with five US highways (and crosses a sixth to the west). A seven-mile section of I-465 from the East Street exit to the interchange with I-74 east near the Marion County Fairgrounds is actually a co-signed route of seven different Interstate, state and US highways: I-74, I-465, US 31, US 36, US 40, US 52 and IN 37. Indiana route 37, which runs concurrent with I-69 from northeast Indianapolis, is slated to be the eventual route of I-69 as it is completed on its proposed routing to Texas. I-465's "branch" highway, I-865 in northwest Indianapolis, allows traffic headed south on I-65 to take the northern leg of the bypass, since the intersection of I-65 and I-465 on the west side of Indy does not allow for a northbound exit on the western leg of the loop. The entire length of the bypass, numbered from its southern interchange with I-65 to the west around the "loop", is about 54 miles – meaning drivers would only need to circle the loop approximately nine and a quarter times to equal the length of the Indianapolis 500. If you did so from the southern I-65/I-465 interchange headed west around Indy, you would hit mile number 500 at the southern edge of Speedway, Indiana.
45. The "Interstates" of Hawaii. The state of Hawaii has three "Interstates" on the island of Oahu; all three connect Pearl Harbor with the other military installations around Honolulu. These Interstates are designated H1, H2 and H3, roughly in that order from the west to the east side of the island. H1 runs along the southern shore of Oahu, from Kapolei, around Pearl Harbor to just past Diamond Head State Monument. H2 extends north from H1 and Pearl Harbor to Wahiawa and the Schofield Barracks Military Reservation. H3 runs from northwest Honolulu at Aliamanu Military Reservation to the Hawaii Marine Corps Base on Kaneohe Bay. A "spur" highway, H-101, has also been designated in recent years. Contrary to popular belief, there has never been any idea of building a Trans-Pacific Freeway from Oahu to the mainland of north America. All three of Hawaii's Interstates have an "Ø" marker at their termini, instead of signposts indicating their end.
46. The "Interstates" of Alaska. Alaska has four highways that are designated as Interstates, though only two sections of them (A1 and A3) have been upgraded to freeway status – and both of those are around the Anchorage area: the New Seward Highway, heading south out of the city to the Kenai Peninsula, and the Glenn Highway, which is 5th Avenue in downtown Anchorage. None of the Alaskan "Interstates" are signed as such. Though the capital city of Juneau does have a state highway running through it (AK 7), it is not considered to be an Interstate highway, making it one of only a handful of state capitals not served by an Interstate. By the way: the Alaska Highway is designated as Interstate A2 between Fairbanks and the state border with Canada and the Yukon Territory – but is not Interstate grade. The closest Interstate to the Alaska Highway is Interstate 5 in Bellingham, WA; the distance between the end at Dawson Creek and I-5's terminus at the Canadian border is approximately 1,180 kilometers (733 miles).
47. The "Interstates" of Puerto Rico. Puerto Rico's Interstates are also unsigned; however, unlike Alaska, the island has many freeways (called "autopistas"), many of them tolled. Puerto Rico's Interstates are designated in the same way as Federal highways, and are maintained as "state" highways. The island's "Interstates" are PRI 1, running from San Juan to Caguas, down to the southern coast and then over to Ponce (numbered mostly as PR 1); PRI 2, running from San Juan along the northern and western coast to Mayaguez, then south and east to Ponce (numbered as PR 2); and PRI 3, running along the eastern coast from San Juan to Fajardo and Roosevelt Roads Naval Station, then south and west to meet up with PRI 1 near Salinas (numbered PR 3).
48. Interstate 676, Philadelphia, PA. The Vine Street Expressway was built in downtown Philadelphia more or less as a "parkway" to connect the Schuylkill Expressway (so named for the river it follows) to the Benjamin Franklin Bridge. Only one problem: at the foot of the Bridge are Franklin Square and the northern end of Independence Mall. Freeway planners knew better than to try to bulldoze American history – the site is supposedly where Franklin flew a kite in his experiments with electricity – so the Interstate designation for the Expressway "ends" at North 6th Street. A spur continues to the north over to the Vietnam Veterans Memorial Expressway (I-95); an entrance to the Franklin Bridge is located near the southern end of Franklin Square. I-676 continues on the other side of the Franklin Bridge in New Jersey, connecting downtown Philadelphia to I-76 on the opposite side of the Walt Whitman Bridge. The two blocks are a rare occurrence on an Interstate: at-grade intersections with surface streets between two sections of a freeway. The westbound section of I-676 has an Interstate-grade exit to I-95, but drivers continuing on I-676 have stoplights at North 7th and 8th Streets. Another slight oddity: the section of I-676 in Pennsylvania is signed east-west, but the section in New Jersey is signed north-south.
49. Interstate 99, central Pennsylvania. This is the freeway that drives "road geeks" crazy. This Interstate is a bypass of US 220 through central Pennsylvania, extending from Bedford north to Bald Eagle, PA. The primary reason for vexation is the old adage: location, location, and location. The route designation does not follow the AASHTO rules for placement of an Interstate; the "proper" location would be along the Atlantic coastline. The credit for the rule breaking comes from Rep. "Bud" Shuster (R-PA), in whose district I-99 runs. Shuster had the I-99 designation written into an appropriations bill, the National Highway Designation Act of 1995, to supersede AASHTO rules. It is currently the second shortest mainline Interstate in the US at just under 70 miles. It is scheduled to eventually extend northward to State College, PA (home of Penn State University) and Interstate 80 at Bellefonte. Eventually, it is scheduled to connect I-80 via Williamsport to I-86 in Corning, NY, bypassing US 15, with a possible extension via I-380 to Rochester. That day is a long way off, however; there are environmental concerns with the section between Bald Eagle and State College. In excavations for the route of the freeway near Skytop Mountain, the rocks were found to contain large amounts of pyrite – a substance that, when exposed to oxygen and water, turns into sulfuric acid. The state has been attempting to get rid of the acidic waste for several months, and construction on the segment between Bald Eagle and State College has been hampered by the environmental issue. Highway observers argue that because of its distance and planned location, a spur designation (such as I-576) would have sufficed. The problem, though, is that I-99 does not have a direct interchange with I-76 or I-70, since the latter two are routed on the Pennsylvania Turnpike. To reach the turnpike, drivers have to exit onto Business US 220 north of Bedford to reach the exit. The freeway extends for a mile and a half beyond the Turnpike to US 30, signed only as US 220.
50. Interstate 70, Breezewood, PA. This is the result of what happens when Federal regulations brush up against the desires of a state government. The Pennsylvania Turnpike is one of the oldest limited-access tolled freeways in the US, pre-dating the Interstate system by nearly two decades. In 1940, an exit was created at a small town named Breezewood where US 30 (then known as the Lincoln Highway) met up with the Turnpike. Because the exit was the first major stop as the Turnpike crossed the Allegheny Mountains, it turned into a tourist trap of sorts, with all sorts of hotels, motels, gas stations and truck stops. When the Interstate Highway Act was signed into law in the 1950's, it was planned that a section of I-70 would meet up with the Turnpike – which was to be designated I-76 – at Breezewood. However, the act specified that Interstates could only be designated on existing toll roads if certain requirements were met: either the money that went into building the roads would be completely repaid by the tolls (and then the toll road would be disbanded), or the state authorities would provide access to an alternate, non-tolled route on a Federally-sanctioned highway – like US 30. The Turnpike Authority didn't want to build a new interchange at Breezewood, since it would require constructing a new on-ramp and a new toll plaza (tolls were taken as vehicles enter the turnpike). Because of this, I-70 was routed to "end" at US 30, about one-quarter of a mile west of the entrance to the Turnpike – and the western leg of I-70. The ramp at the end of the eastern leg of I-70 leads to a stretch of highway that has 37 restaurants, gas stations, truck stops and motels – all on that quarter-mile strip between the two exits on US 30. The "gap" remains because the owners of the various businesses have allies in the Pennsylvania state government to prevent any changes to the "interchange."