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Gaps in US highways
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Why some US routes consist of two separate segments
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The initial reason I envisioned this page was because there were a couple factoids that needed to be addressed: 1.) US routes do not exist within the boundaries of Yellowstone National Park, and 2.) for that reason some US highways consist of two non-contiguous segments. But then of course there are other US routes with gaps that have nothing to do with Yellowstone. So ultimately I decided to create a page which covers all of the US routes that have various types of discontinuities.
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Some of these discontinuities have been acknowledged by AASHTO, while others have not, so they can be classified into two broad categories: official gaps and unofficial gaps.
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Official gaps
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By "official" I mean either 1.) gaps that were defined in AASHTO's route log, or 2.) gaps that were not mentioned in the route log, but were nevertheless made official by AASHTO action (or AASHO prior to 1973). We will begin with the first type, and Yellowstone National Park provides several examples.
Since the very beginning of the US route system, US highways have never gone through the Park. Actually, there is one exception to that statement (which we will discuss later), so to be more accurate: US routes have never gone through the main part of Yellowstone, i.e. never along any segment of the Grand Loop Road. Rather, US highway designations have always ended at the National Park boundary. However, some of those designations resume on the opposite side of the Park. From the outset, there were examples of both; this is a clip from the US highway map that AASHO released in November 1926, which accompanied their announcement of the brand-new US route system: |
c. 1926, AASHTO
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US 87W
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At the time, US route 191 ended at Yellowstone's west entrance, while US 20 ended at the east entrance (as a matter of fact, US 20[E] still ends there). Notice that US 87W was shown on the north side of Yellowstone as well as the south, but it was not shown as passing through the Park. That was reiterated in AASHO's inaugural route log of April 1927. Notice that the description of US 87W indicated a gap in the route between Gardiner (i.e. Yellowstone's north entrance) and the south entrance:
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US 89
US 87W no longer exists. To the north of the Park, it followed what is now US 89, and to the south it followed what is now US 287. Those designations were implemented already by the mid-1930s, and were illustrated on this map:
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c. 1939, Rand McNally
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Also by that time both US 12 and US 14 had been extended to the Park, ending at the northeast and east entrances, respectively. US 20 still ended at the east entrance, but US 191 no longer quite made it to the west entrance. Instead it turned north at West Yellowstone, becoming the first (and only) US route to be signposted within the boundaries of Yellowstone (more on that below). US 89 had replaced US 87W as the only US route assumed to go "through" the Park (even though the US 89 designation did not exist within the Park itself). Here is the relevant part of that route's entry from AASHO's 1935 route log:
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"Implied" routes
That is a term that is often used in the road enthusiast community, as in "US 89 had an implied route through Yellowstone". I have no objections to that term, as long as we can agree on exactly what is "implied". Since there were (and are) US routes with the same number on opposite sides of the Park, it is obvious there was an implication that drivers on one of those US highways could pass through Yellowstone and then resume travel on that same route. However, no specific route through the Park has ever been implied. For example: is US 89 traffic supposed to use the west Grand Loop or the east Grand Loop? That is a question that cannot be answered, because either option would work, as would a hybrid option using some combination of both sides. So it is up to each individual driver, and NPS has never made any attempt to influence that decision by defining the route of US 89 through Yellowstone.
So already by 1935, US 89 consisted of two separate sections. As of 2020, the mileage breakdown was as follows:
A note about US highway nomenclature: anything I have put in [brackets] is not an official part of the US route designation. For example, both US 89[N] and US 89[S] are signposted in the field simply as "US 89". AASHTO's route logs differentiated the two by referring to them as "US 89 north section" and "US 89 south section". On this page (and throughout this website) I have streamlined this nomenclature by using [N] and [S], or in other cases [E] and [W].
- US 89[N]: 399.7 miles (all in MT)
- Undefined (and therefore unmeasurable) route through Yellowstone
- US 89[S]: 839.3 miles (WY through AZ)
A note about US highway nomenclature: anything I have put in [brackets] is not an official part of the US route designation. For example, both US 89[N] and US 89[S] are signposted in the field simply as "US 89". AASHTO's route logs differentiated the two by referring to them as "US 89 north section" and "US 89 south section". On this page (and throughout this website) I have streamlined this nomenclature by using [N] and [S], or in other cases [E] and [W].
US 20
As noted previously, what is now US 20[E] was around from the very beginning, running between Boston and Yellowstone's east entrance. Then in about 1940 a separate section of US 20 was commissioned: US 20[W] runs from West Yellowstone to Oregon. Here is the 2020 mileage of those sections:
- US 20[W]: 856.8 miles (OR through MT)
- Undefined (and therefore unmeasurable) route through Yellowstone
- US 20[E]: 2346.5 miles (WY through MA)
US 287
US 287 was commissioned in 1935, with its north end at Yellowstone's south entrance. In 1965 US 287 was implied to extend through the Park to West Yellowstone, then continuing north from there. As of 2020 US 287's two sections measured as follows:
- US 287[N]: 281.2 miles (all in MT)
- Undefined (and therefore unmeasurable) route through Yellowstone
- US 287[S]: 1604.5 miles (WY through TX)
US 191
Previously we discussed how US 191 initially began at West Yellowstone and went south from there. Then in 1934 US 191 was extended north from West Yellowstone. But in about 1980 the US 191 designation was removed from its original segment (West Yellowstone to Idaho Falls), and instead US 191 was assumed to pass through the National Park, re-emerging at Yellowstone's south entrance.
- US 191[N]: 440.0 miles (MT and WY)
- Undefined (and therefore unmeasurable) route through Yellowstone
- US 191[S]: 1211.3 miles (WY through AZ)
So that makes four US routes (20, 89, 191, and 287) that have implied but undefined connections through Yellowstone. But there are other US highways that have gaps which are unrelated to Yellowstone:
US 2
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US 2 is the lone example that involves an international boundary. US 2[E] runs through a few New England states and then ends essentially at the Canada border south of Montreal, while US 2[W] runs between Michigan and Washington. This clip from the 1927 route log shows described the routes on both sides of that discontinuity:
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Historically US 2[W] could be conceptualized as a "reappearance" of US 2[E] into the U.S. from Canada at Sault Ste. Marie. But in 1984 the segment of US 2 between SSM and St. Ignace was decommissioned, so now it makes even less sense to think of US 2 as a single highway with an implied routing through Canada. Rather, US 2 actually consists of two separate routes that happen to share the same number.
US 422
In the original 1926 list of US routes, there was only one US 422: the one running between Cleveland and Ebensburg PA. But Pennsylvania did not begin signposting their routes until 1928 because they had numerous objections to AASHO's plan, and they threatened to leave their US routes unmarked unless AASHO acquiesced to their demands. One of their requests was to re-number the segment of US 120 between Philadelphia and Reading as US 422. AASHO immediately recognized that this would create two non-contiguous segments of US 422, and in June 1927 they questioned Pennsylvania about it:
Undaunted, Pennsylvania instructed AASHO to forge ahead with the change...
...and thus was born the strange situation with two separate routes numbered US 422. I mean "strange" in the sense that all other official gaps in US routes were there because of jurisdictional issues, i.e. because a foreign country or a National Park was situated between the two highway segments. But that was not the case with US 422. Rather, this gap came about because Pennsylvania's ideas about the US route system were not in complete alignment with AASHO's original intent, and within their own boundaries Pennsylvania was determined to mold the US route system into something that conformed to their slightly peculiar vision.
US 10
It should be acknowledged that in AASHTO's latest route log, there was one additional highway that was listed as having two separate sections: US 10. This was because of its ferry segment across Lake Michigan. It seems odd that US 10 was considered to have two segments, whereas US 9 (which also has a ferry segment) was listed as a single route. Regardless, the point is moot now, because a 2015 AASHTO action made the Ludington-Manitowoc ferry an official part of US Route 10. So US 10 no longer has an official gap in its route. However, I do consider both US 9 and US 10 to have unofficial gaps; I discuss those more later on this page.
A bit more about National Parks
Above I mentioned that US 191 is the one exception to the statement that no US routes go through Yellowstone (this blog post has more info). To be clear: US 191 does have a gap through the Park, between West Yellowstone and the south entrance (as noted above). However, the Montana segment of the highway between West Yellowstone and Big Sky is all considered by AASHTO to be part of US 191. That includes a 20.2 mile segment that crosses inside the northwest corner of Yellowstone, although there is no entrance gate/fee station on either end. US 191 is reportedly even signposted through that Yellowstone segment (which includes a 5.9 mile stretch that passes in and out of Wyoming).
So it is not entirely accurate to say that no US routes exist in Yellowstone. Moreover, it is absolutely incorrect to assume that the National Park Service has a broad policy that disallows US route designations within any of its holdings. For example, US 34 and US 36 both run through Rocky Mountain NP; US 33 and US 211 both run through Shenandoah NP. So it is up to individual Parks to decide whether or not to signpost US routes within their boundaries. However, there is another National Park that is similar to Yellowstone in terms of how it handles US routes, and that brings us to another subcategory:
So it is not entirely accurate to say that no US routes exist in Yellowstone. Moreover, it is absolutely incorrect to assume that the National Park Service has a broad policy that disallows US route designations within any of its holdings. For example, US 34 and US 36 both run through Rocky Mountain NP; US 33 and US 211 both run through Shenandoah NP. So it is up to individual Parks to decide whether or not to signpost US routes within their boundaries. However, there is another National Park that is similar to Yellowstone in terms of how it handles US routes, and that brings us to another subcategory:
Gaps made official by AASHTO action
At the time of its 1952 extension into Tennessee, and for almost the next two decades, US 441 was signposted through Great Smoky Mountains National Park. But at their November 1970 meeting, AASHO approved a National Park Service request to remove US 441 signs through the Park, and ever since then US 441 has had a gap. Here is an excerpt from the actual minutes of that meeting:
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However, for some reason even AASHTO's latest route log still did not show US 441 as having a north section and a south section. Nevertheless, the action noted above clearly indicates that US 441 no longer exists within GSMNP, so it serves as an example of an official gap despite not being reflected in the route log. Here is the mileage breakdown as of 2023:
As of the last time I checked Google Maps, the former segment of US 441 through GSMNP was still labeled with a US 441 shield; you can check whether that is still the case by viewing this next map. The red segment has not officially been designated US 441 since 1970; the Park refers to it simply as Newfound Gap Road: |
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In addition to US 441, there are at least a couple more US routes that have similar gaps... at least in the sense that they are not noted in the route log but were still made official by AASHTO action. The difference is that I consider them to be... well, "illegitimate" for lack of a better word. I will discuss those more towards the end of this page. But for now we should skip to the next major category:
Unofficial gaps
By "unofficial" I mean the gaps in these routes were neither created by AASHTO nor are they recognized by AASHTO. Nevertheless, it would be absurd to act as if they do not exist. I have classified these unofficial gaps into two subcategories: "defacto gaps" (which physically cannot be traversed) and "perceived gaps" (which are not technically gaps but can easily be perceived that way), and under each of those headings are additional subclassifications. Let us begin with real, physical gaps:
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Defacto gaps
One of the best examples is US 87 in Wyoming. In the 1990s a segment of US 87 was damaged by a series of landslides (the red segment shown on the following map). For various reasons WYDOT opted not to rebuild the road, and instead asked AASHTO to shift the US 87 designation onto SH 193 (blue segment). AASHTO refused, suggesting instead that WYDOT direct US 87 traffic onto I-90. WYDOT rejected that idea, and ever since then the whole situation is at an impasse. AASHTO still considers US 87 to run along the red and orange segments, yet that road literally cannot be used for the purpose of through traffic. WYDOT has changed the geometry of the highway junctions such that US 87 traffic seamlessly flows onto SH 193 and back again, but they have not signposted SH 193 as US 87 (despite the US 87 labels shown on this Google Map):
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Seasonal gaps
US 34 and US 212 both go over high-altitude mountain passes that receive heavy snowfall. These road segments are not cleared of snow and are closed to traffic every winter. And winter lasts a long time in the Rockies: in fact, on an annual basis these sections are actually closed to traffic for a longer period of time than they are open. The red segments shown on the maps below are closed annually, which has the effect of dividing their respective US routes into two disconnected sections:
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Perceived gaps
Above we briefly touched on the fact that US 9 and US 10 both have ferry segments. Those ferries are officially considered part of the US routes, so technically there is no gap in US 9 or US 10. Nevertheless, these segments have a significant difference when compared to any other US highway, because obviously neither the car nor the driver has an active role while in transit between the ferry docks. So these segments of US 9 and US 10 could be thought of as "perceived gaps due to mode of transportation". And one might be particularly inclined to perceive a gap in US 10 when they see the erroneous "US 10 Ends" sign that Michigan has been known to post at the approach to the Ludington ferry dock.
Signage gaps
Motorists also perceive a gap in a US route in places where no US highway shields are posted on the road to reassure them, or to direct them to make a turn, or to take an exit. There are innumerable examples of missing signs, and in most cases the lack of signage is unintentional on the part of the state DOT. Signs get damaged, or they fade to illegibility, or they get stolen. Or sometimes the sign maker (either the DOT sign shop or a private contractor) omits a US route shield simply due to oversight or human error.
However, there are some DOTs that intentionally do not sign some of their US routes. Most often this is done in places where the US highway joins with an Interstate highway, but only the Interstate route is signposted. From AASHTO's perspective the US route exists along with the Interstate, but from a driver's perspective there is nothing to inform them that the US route exists along that segment. The reason commonly given for this type of signage policy is to reduce expense, driver confusion, and "sign clutter". Arkansas is known for this practice, as are some other states, but it is probably Colorado that is most notorious for it. As just one example: between north Denver and the town of Byers, US 36 traffic ostensibly follows a 43-mile segment along Interstates 70 and 270. However, there is no signage directing US 36 traffic onto those Interstates, nor is there a single reference to US 36 anywhere along that entire stretch. And many other US routes that enter Colorado have a similar signage gap where they join an Interstate, including US 6, US 24, US 40, US 50, US 85, US 87, US 287.
However, there are some DOTs that intentionally do not sign some of their US routes. Most often this is done in places where the US highway joins with an Interstate highway, but only the Interstate route is signposted. From AASHTO's perspective the US route exists along with the Interstate, but from a driver's perspective there is nothing to inform them that the US route exists along that segment. The reason commonly given for this type of signage policy is to reduce expense, driver confusion, and "sign clutter". Arkansas is known for this practice, as are some other states, but it is probably Colorado that is most notorious for it. As just one example: between north Denver and the town of Byers, US 36 traffic ostensibly follows a 43-mile segment along Interstates 70 and 270. However, there is no signage directing US 36 traffic onto those Interstates, nor is there a single reference to US 36 anywhere along that entire stretch. And many other US routes that enter Colorado have a similar signage gap where they join an Interstate, including US 6, US 24, US 40, US 50, US 85, US 87, US 287.
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Illegitimate gaps
Above I mentioned that there are some gaps which were made official by AASHTO action, yet I consider them to be illegitimate. Why? These are decisions that were made in recent years, a timeframe during which AASHTO's Special Committee on Route Numbering often seems to operate as if they have lost sight of some basic conditions that need to be in place before a road can be approved as a US route. One seemingly-obvious requirement of a US route is: motorists should be able to drive the route from one end to the other. Yet in 2009 AASHTO approved a change to a US route that made it impossible for drivers to follow that route. I will try to explain using this screenshot taken from OTIS (CDOT's Online Transportation Information System). The basemap shows all roads in white; roads overlaid in red are CDOT's responsibility. The highway on the left is I-25. On the right is CDOT's definition of US 85:
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CDOT, accessed Jan. 2023
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Towards the upper left, US 85 uses a freeway overpass (which provides no access to I-25), and then upon resuming a northerly direction, US 85... just ends. According to CDOT, US 85 continues north from that point by using I-25, but that is easier said than done, because there is no way for drivers to make that movement. Traffic continuing north on Venetucci Boulevard is on a locally-maintained road that CDOT insists is no longer US 85. So the only other option would be to turn around, backtrack about 1.5 miles to Academy Boulevard, and then use that to get on I-25. But Academy is no longer a state highway either, and CDOT has not posted signs directing US 85 traffic to use Academy.
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This is a colossally ridiculous arrangement, and AASHTO never should have approved it. In their 2009 application to AASHTO, CDOT included a small-scale, low-detail map which served to downplay the fact that US 85 has no access to I-25 at that point. AASHTO should have told CDOT, essentially, "If you want this laughable arrangement to be part of your state highway system, that's your call, but you do not have permission to use a US route shield on a dead-end segment like that. You may move US 85 traffic over to I-25, and change this nine-mile segment of US 85 to a state highway designation. Or you may come up with a different solution, but US 85 must be a continuous route."
Unfortunately, that was not the last of the nonsense coming out of Colorado. In 2015 CDOT removed from their inventory a one-mile segment of US 6 in Rifle, turning it over to the City for maintenance. On this map, US 6 runs horizontally along the north bank of the river, and you can see that there is no red line where it passes through the main part of Rifle: |
CDOT, accessed Jan. 2023
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Across the U.S. there are many, many segments of US routes like that (i.e. they are maintained not by the state DOT but rather by a more local entity, such as a county, a township, a city, etc.) I am not aware of any other state that reports those situations to AASHTO, but for whatever reason CDOT felt the need to get AASHTO involved. And rather than simply reporting it to AASHTO, they actually asked AASHTO to decommission this one-mile segment of US 6. AASHTO should have responded, "This is of no concern to us, and we are not going to create a tiny discontinuity in the middle of a 3200-mile route simply because it's maintained by a municipal government. If you don't want to allow a local government to signpost a US route, then you are welcome to move US 6 traffic onto I-70, but US 6 must be a continuous route." So how did AASHTO actually respond? Well, they... just approved it.
Research and/or photo credits: Tom Fearer; Dale Sanderson
Page originally created 2023;
last updated Jan. 8, 2023.
last updated Jan. 8, 2023.
