List of gaps in Interstate Highways

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Dwight D. Eisenhower National System of Interstate and Defense Highways
Interstate 95 marker Interstate 70 marker
Highway shields for Interstate 95 and Interstate 70, highways with true gaps and freeway gaps
Interstate Highways in the 48 contiguous states
System information
Formed: June 29, 1956[1]
Highway names
Interstates: Interstate X (I-X)
System links
I-70 briefly follows an at-grade portion of US 30 with traffic lights in Breezewood, Pennsylvania

There are gaps in the Interstate Highway system, where the roadway carrying an Interstate shield does not conform to the standards set by the Federal Highway Administration (FHWA), the body that sets the regulations for the Interstate Highway System. For the most part, the Interstate Highway System in the United States is a connected system, with most freeways completed; however, some Interstates still have gaps. These gaps can be due to unconnected segments of the same route or from failure of the road to fully conform to Interstate standards by including such things as at-grade crossings, traffic lights, undivided or narrow freeways, or movable bridges (lift bridges and drawbridges). This article deals with present-day gaps, as such examples were far more numerous during construction of the Interstate Highway System and the upgrading of existing roads to meet these standards, which did not occur everywhere at the same time. Temporary gaps, such as lane closures that reduce traffic to one lane and reduce speed limits, are also excluded.

True gaps[edit]

True gaps are where two disjoint sections of road have the same Interstate highway number and can reasonably be considered part of "one highway" in theory, based on the directness of connections via other highways, or based on future plans to fill in the gap in the Interstate, or simply based on the shortness of the gap. The two sections are either not physically connected at all, or they are connected but the connection is not signed as part of the highway. It should be noted that most of these gaps (except for the one on I-95) exist because the two segments are actually two unrelated highways that were built at different times, but assigned the same number; many times, the same number was assigned to the second segment with the intention of eventually connecting it to the first segment.

Freeway gaps[edit]

Freeway gaps occur where the Interstate is signed as a continuous route, but part or all of it is not up to freeway standards. This includes drawbridges where traffic on the Interstate can be stopped for vessels. This does not include facilities such as tollbooths, toll plazas, agricultural inspection stations, or border stations.

At-grade intersections and traffic lights[edit]

Surface street section of I-78 in Jersey City, New Jersey

Several Interstates in rural areas of the U.S. have at-grade intersections (including median breaks) with minor farm access roads. This is usually due to the lack of an old highway; the need to provide access to property that was accessed via the road prior to its upgrade to an Interstate; and the high cost to construct an interchange for the small amount of traffic that would use such a connection or to build a frontage road parallel to the freeway to the nearest interchange. Other at-grade intersections are restricted to municipal service vehicles, of which make it easier for maintenance to be done in places like in the mountains as well as tollways.

Undivided and narrow freeways[edit]

Two-lane stretch of I-93 through Franconia Notch in New Hampshire
Two-lane stretch of I-81 on the Thousand Islands Bridge crossing part of the Saint Lawrence River
The Mackinac Bridge, which carries I-75, has no hard shoulders, and only has a 4-inch-tall (10 cm) divider between the opposing directions

This section addresses two-lane freeways and other narrow or undivided freeway sections of the Interstate, excepting instances of continuing routes using one-lane ramps and merge leads. Narrow gaps between opposing directions with jersey barriers taller than four feet (1.2 m) are excluded from this section; therefore the separation criteria is really either a 4-foot-tall (1.2 m) wall, or a 100-foot-wide (30 m) median, whichever is greater.

  • I-40's western 15 miles (24 km) in North Carolina in the Harmon Den Wildlife Management Area has several S-curves, a Jersey barrier with extremely narrow left shoulders and a few at-grade intersections albeit in RIRO style.
  • I-55 has only one lane for northbound through traffic for several hundred feet at the Poplar Street Bridge in St. Louis, Missouri, where the highway approaches the Poplar Street Bridge, which carries the highway over the Mississippi River toward East St. Louis, Illinois. A similar situation exists on the southbound lanes as I-55 must travel down a one-lane twisty ramp onto the main highway once traffic enters the Missouri side of the bridge. In 2015, the Missouri Department of Transportation will widen the Poplar Street Bridge to allow northbound traffic two lanes onto the bridge.[11]
  • Interstate 70 is one-lane only for these following reasons:
  • The Murray Baker Bridge, which carries I-74 over the Illinois River in Peoria, Illinois, has no shoulders, which makes it too narrow for Interstate standards. Trucks of all sizes, however, are permitted on this bridge.
  • The Mackinac Bridge, which carries I-75 over the Straits of Mackinac between St. Ignace and Mackinaw City, Michigan, has no wide median or hard shoulders due to space constraints. Nor does it have a Jersey barrier; instead, it has either a 4-inch-tall (10 cm) yellow divider between the opposing directions (where the inner lanes are a metal grate) or a flat double-yellow line (where the inner lanes are paved). The speed limit is also reduced to 45 mph (70 km/h) for cars and 20 mph (30 km/h) for trucks. The highway returns to Interstate standard for about 50 miles until it reaches the Sault Ste. Marie International Bridge, which carries undivided lanes to the Canada–US border in the middle of the bridge, where I-75 terminates.
  • A short stretch of I-278 is two-lane in Astoria, New York, and has height limits due to its being on the Grand Central Parkway, a height-restricted parkway.
  • The Thousand Islands Bridge, which carries I-81 over part of the Saint Lawrence River, is an undivided two-lane road.
  • I-93 is a two-lane divided parkway, or a "super two", through Franconia Notch in New Hampshire. A four-lane Interstate Highway was once proposed here, but the concept was abandoned because of environmental concerns, in part because of vibrations that could harm the Old Man of the Mountain rock formation (prior to the formation's 2003 collapse). This section of highway was for many years marked as US 3 and "To I-93", but these have now been replaced with regular I-93 signs. The Federal Highway Act of 1973 exempts this stretch from the Interstate Highway standards that apply elsewhere, and this highway is considered to be I-93 for all practical purposes.[12]
  • Most of Interstate 476 under the jurisdiction of the Pennsylvania Turnpike Commission has a four-foot (1.2 m) median with a Jersey wall. This is because the Northeast Extension was constructed in the 1950s and used a narrow profile construction, which at one point had a double yellow line. Portions of it extending north from milepost 20 are being widened to six lanes with a 24-foot (7.3 m) median.
  • Some stretches of Interstate highway use a barrier transfer machine on some bridges to convert inner lanes from one direction to the other, where it would be too costly to upgrade/rebuild to a higher-capacity bridge. In any case the traffic distribution is strongly asymmetric depending on the hour of the day. This kind of bridge typically contains undivided lanes without the flexible Jersey barrier that is manipulated by machines.

Movable bridges[edit]

A six lane freeway in an urban area with a vertical lift bridge in the distance. A green sign with flashing lights on the right side of the road reads Drawbridge ahead 700 feet.
I-280 westbound approaching the movable Stickel Bridge over the Passaic River in New Jersey

By Interstate standard, all bridges on the Interstate system must be fixed as to not interrupt the flow of traffic. Several bridges on the system, however, are movable:

Other movable bridges on the Interstate System have been replaced after spending many years as part of the system. These include:

  • I-75 had a bascule bridge from 1960 to 1988 at Zilwaukee, Michigan, just north of Saginaw; the high-level Zilwaukee Bridge replaced it on December 23, 1987, for northbound traffic, and on September 19, 1988, for southbound traffic.[17] Interstate 675 was built as an in-town bypass of the bascule bridge prior to the construction of the tall Zilwaukee bridge. Since the completion of the tall Zilwaukee bridge in 1987, I-675 has had less traffic than its capacity; though it is a feasible detour for bridge, or other maintenance between both ends of the loop.
  • I-280 formerly had a drawbridge, the Craig Bridge, in Toledo, Ohio. The fixed-span Veterans' Glass City Skyway replaced the drawbridge on the Interstate Highway in 2007.

Freeway-to-freeway crosspaths without direct connection[edit]

Connection gaps[edit]

Auxiliary Interstates (also known as three-digit Interstates) are intended to connect to their parent either directly or via a same-parented Interstate (like I-280 in California being connected to I-80 via I-680). Often, these connection gaps occur to eliminate concurrencies between other three-digit routes. Freeway gaps (signed or unsigned) that officially connect auxiliary routes to the parent are excluded.

Current day examples[edit]

  • I-210 in California does not currently connect directly to I-10 or any of its spurs according to freeway signage. It was signed all the way to I-10 until 1998, when California State Route 57 replaced the portion of I-210 through Covina and San Dimas to provide a proper connection to current State Route 210. The former portion of I-210 now known as SR 57 still remains on the Interstate Highway System federally defined as Interstate 210[18] maintaining its connection to I-10, but it is not signed as per Caltrans tradition to sign state highways by their state definition over their federal definition. State Route 210, built as an extension to replace Route 30, connects to I-10, and California is petitioning to have that portion signed as I-210 as well. When that happens, this gap will close.
  • Interstate 269 is near Memphis, Tennessee, but doesn't actually connect to Interstate 69 yet, since I-69 is still under construction.
  • None of the spurs of I-78 (I-278, I-478, I-678, I-878) connect to its parent, nor is there any surface-street with a state route designation with the same number that continues with a solid connection. (see disputed gaps below)
  • Interstate 585 near Spartanburg, South Carolina uses a business loop, albeit in freeway form of I-85, but this puts the example in some dispute of consensus (see disputed gaps below)
  • Interstate 495 doesn't currently have any official connection to Interstate 95, though it has a FUTURE sign along US-64 in North Carolina until as far east as Interstate 95.
  • Numerous three-digit Interstate routes are unsigned on some portions, which would lead some to think they were "connection gaps". However these aforementioned "connection gaps" don't even have internal unsigned concurrencies on other Interstate highway segments between the "parent route" and signed terminus.

Disputed gaps[edit]

Gaps where different criteria constitute contradictory circumstances.

  • I-265—the Indiana portion of I-265 does not yet connect with the Kentucky portion. Each of the two segments, circling the outskirts and suburbs of Louisville, ends before crossing the Ohio River, making them completely in separate states, thus following numbering guidelines. A bridge to connect the two segments is currently under construction.[19]
  • None of the spurs of I-78 (I-278, I-478, I-678, I-878) connect to its parent. I-78 was planned to extend through New York City and end as two branches, where I-295 and I-695 now end at I-95. I-478 comes the closest, and would have intersected if the Westway project were not canceled; I-278, the only I-78 spur to leave New York City, was planned to extend northwest to I-78 at Route 24. Since all the spurs are interconnected, only one of them needs to be eventually connected to its parent route for all of them to conform to numbering standards.
  • I-585 used to connect with I-85 in Spartanburg, South Carolina, but I-85 was moved to a new bypassing route and the section of I-85 where I-585 now ends was redesignated Business I-85. The signed connection to I-85 is via a surface section of US 176.
  • I-90 at the Chicago Skyway—historically, the Skyway was commonly considered to be, and was signed as, part of I-90 (originally I-94). However, around 1999, the City of Chicago determined it may never have applied for approval to sign it as an Interstate. (It also is not designed to Interstate standards.) The city re-signed the Skyway, and it is now mostly posted with "TO I-90/94" signs with a few older signs remaining. However, the Illinois Department of Transportation has always and continues to report the Skyway as part of the Interstate system, and the Federal Highway Administration still considers it as such. An FHWA legal memo says "There is no doubt about it. The Chicago Skyway is officially part of I-90 that (has) always been included in the Dwight D. Eisenhower National System of Interstate and Defense Highways."[20][21]
  • The northern end of the I-99 freeway ends less than 1 mile (1.6 km) from I-80 in Pennsylvania, and motorists can continue north on US 220/PA 26 along the surface street to grade-level ramps to access I-80. Once the extension of I-99 is completed, it will be concurrent with I-80 to the east.

See also[edit]


  1. ^ 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. 
  2. ^ "Report to SCOH May 19, 2012" (PDF). [dead link]
  3. ^ "Alliance for I-69 Texas: More Houston Areas Freeway Added to Interstate 69" (Press release). 
  4. ^
  5. ^ Malme, Bob. "I-73 Segment 4". Self-published. Archived from the original on January 1, 2009. Retrieved November 19, 2009. [unreliable source]
  6. ^ Malme, Bob. "I-73 Segment 9/I-74 Segment 10". Self-published. Archived from the original on December 30, 2008. Retrieved November 19, 2009. [unreliable source]
  7. ^ Malme, Bob. "I-74 North Carolina Progress Page". Self-published. Archived from the original on July 25, 2010. Retrieved August 28, 2009. [unreliable source]
  8. ^ Roig-Franzia, Manuel (November 22, 2001). "The Town That Stops Traffic: Travelers Encounter Way Station as Way of Life in Breezewood". Washington Post. p. B1. 
  9. ^ Google (August 28, 2009). "Intersection of 14th St (ostensibly 78 West) and Erie St" (Map). Google Maps. Google. Retrieved August 28, 2009. 
  10. ^ Staff. "Road & Highway Facts". Michigan Department of Transportation. Retrieved October 28, 2014. 
  11. ^ "I-64 Corridor Improvements" (PDF). 
  12. ^ Weingroff, Richard (April 7, 2011). "Interstate System Conditions and Performance". Highway History. Federal Highway Administration. Retrieved August 20, 2012. 
  13. ^ Project staff. "Home". Columbia River Crossing. Oregon Department of Transportation and Washington State Department of Transportation. Retrieved August 28, 2009. 
  14. ^ Read, Richard (July 5, 2013). "Bridge Funds to Nowhere: Some of the $175 million in work for the now-defunct Columbia River Crossing might be useful someday, but much of it is just gone". The Oregonian. Portland, OR. p. A1. Retrieved July 5, 2013. 
  15. ^ Highway Information Services Division (December 31, 2007). Highway Location Reference. Maryland State Highway Administration. Retrieved April 15, 2009. 
  16. ^ Highway Services Division (2010). "Movable Bridges on State Maintained Highways" (PDF). Maryland State Highway Administration. Retrieved October 18, 2010. 
  17. ^ Staff writer (September 19, 1988). "Zilwaukee Bridge Now Open North, South—Partly". Toledo Blade. p. 1. 
  18. ^ Federal Highway Administration. National Highway System: Los Angeles, CA (PDF) (Map). Scale not given. Federal Highway Administration. Retrieved February 5, 2012. 
  19. ^ "Home". Ohio River Bridges Project of Kentucky and Indiana. Kentucky Transportation Cabinet and Indiana Department of Transportation. Retrieved August 28, 2009. 
  20. ^ Office of Operations. "Tolling and Pricing Program". Federal Highway Administration. Retrieved August 28, 2009. 
  21. ^ Samuel, Peter (June 29, 2005). "Skyway Is Interstate 90 Unless State Withdraws Reports: Feds". TollRoadsNews. Archived from the original on September 22, 2008. 

External links[edit]