Extreme points on the US highway system

Wikipedia hosts an interesting article (or at least it's interesting to geography nerds like me) which lists the extreme points in the United States (e.g. the northernmost points in the US, the southernmost points, and so on).  This blog post could be considered a subset of that article, as I am discussing the extreme points on the US highway system.  (Since the US route network exists only in the 48 contiguous states, Alaska and Hawaii are outside the scope of this post, not to mention all US territories.)  We will start with the most obvious, and from there it will get more complicated.

Easternmost points

Most map projections make it rather clear that Maine is the easternmost state (although it is even farther east than many people realize).  The easternmost US route terminus is where US 2 almost reaches the Canada border, about three miles east of its junction with US 1 in Houlton ME:

Historically (before I-95 was built) US 2 actually did reach the Canada border.  However, even that was not the easternmost point on the US route system.  At Houlton, the US-Canada boundary is a surveyed line running due north-south.  But about 13 miles south of Houlton, the boundary is defined by the St. Croix River and its headwaters.  That river flows to the southeast, and US 1 serves some of the towns in that valley, thus swinging out even farther east than Houlton.  Because of that, the easternmost point on the US route network is located in the town of Perry ME.  The exact point is 300 feet north of US 1's bridge over the Little River, at its intersection with Shore Road:

There are other geographical points of interest in the immediate area.  Two miles further north on US 1 is a marker denoting the point where the highway crosses the 45th parallel (halfway between the equator and the north pole).  3/10ths of a mile south of the Little River bridge is the junction with state highway 190, which leads to Eastport, which is the easternmost city in the US.  Not far from there is Lubec (the easternmost municipality), and Quoddy Head (which is the easternmost point of land in the contiguous US).

Southernmost points

The most common projection used for maps of the US tends to make Texas look like it extends farther south than Florida.  But in reality, the southernmost point in Texas is on the same latitude as Hialeah FL.  That means Miami, and all points to the south of there, are farther south than anyplace in Texas.  So the southernmost US route terminus is where US 1 ends in Key West FL:

US 1 was extended south to Key West in 1939; prior to that extension the southernmost endpoint was where US 1 and US 94 shared a common terminus in Miami.  

However, the Key West terminus is not the southernmost point on the US route system.  The Key West terminus is located on Whitehead Street at its intersection with Fleming Street.  From Fleming, northbound US 1 actually begins by heading five blocks to the southeast on Whitehead, before turning northeast onto Truman Avenue.  So that turn in US 1 marks the southernmost point on the US route network.

From that intersection, if you continue southeast on Whitehead for another four blocks, you reach another extreme point, or at least a reasonable substitute: the well-known Southernmost Point Buoy.  That is a tourist-friendly, publicly-accessible location for the marker, but it is not actually the southernmost point.  There are some points on Ft. Zachary Taylor Beach which extend further south, but access requires an entry fee.  And Whitehead Spit on the nearby Truman Annex extends even further south, but the Naval Air Station is not accessible to the public.

From the buoy, heading back northwest on Whitehead to the aforementioned southernmost point on US 1, there is a sign pointing out both directions on US 1.  Google Street View imagery from Nov. 2025 shows someone taking a photo of that sign:

This is amusing to me, because in my imagination she thought she was photographing the terminus of US 1, and she may have been wondering why there were no other tourists around.  In actuality she was indeed capturing an interesting point on US 1, but not the point that most Key West visitors intend to photograph.

Westernmost points

The westernmost US route terminus is where US 199 ends at its junction with US 101 in Crescent City CA:

That may be a little surprising, since US 199 is considered a north-south route (one might expect that an east-west route would extend farther west).  Historically US 101 in Crescent City ran slightly farther west, and therefore US 199's historic terminus was a bit farther west as well.  US 199 is only slightly farther west than several other current and historic endpoints along the northwest coast of the US, with the closest contenders both in Oregon: US 20[w] in Newport and historic US 28 in Florence.

And the westernmost point on a US route is indeed in Oregon; specifically in Port Orford.  If one starts at 16th Street and goes exactly one mile north on US 101, they will be at the westernmost point on the US highway system (where the road makes a tiny curve to the west before angling back east again):

Northernmost points

Typical maps of the US make it appear that Maine extends farther north than it actually does.  In reality the 49th parallel is farther north than anyplace in Maine.  Once you realize that, then you might conclude that the northernmost US route would be a tie, since there are a dozen US routes (and historically more) that end along the Canada border between Washington and Minnesota, where all endpoints are nominally at 49 degrees north latitude.  

However, while the legal definition of the boundary is 49 degrees north, the defacto boundary is the line that was actually surveyed along the frontier and accepted by the two nations.  The initial surveying work began during the 1850s, and it was completed in the 1870s.  Then a resurvey was done during the first decade of the 20th century (i.e. over 100 years ago).  Surveyors back then used tools that would be considered rudimentary today.  Given the equipment available to them at the time, they did a remarkably accurate job.  Nevertheless, there are some places where the boundary as surveyed dips to the south of the 49th parallel, and there are other places where the border veers to the north of the parallel.  I have read that if one measures the area of land that technically should have been in Canada, and compares that to the acreage that should have been in the US, then Canada has a net gain of 67 square kilometers.  I'll have to take their word for that.  But the question I set out to answer was this: 

Given the slight deviations along what was intended to be a straight line of latitude, is there a US route that extends farther north than all of the others?  

As it turns out: yes, there is.  Currently the northernmost US route terminus is where US 95 reaches the Canada border, because at Eastport (ID) the boundary line is roughly 200 feet north of the 49th parallel:

Historically the northernmost terminus was US 99, because in Blaine (WA) the Canada border is about 500 feet north of the 49th parallel.  That point is quite well-known because it is the same place where Interstate 5 ends today: the Peace Arch border crossing:

Note there is one area of the 48 states that lies significantly north of the 49th parallel: Minnesota's Northwest Angle.  There, one can find a Northernmost Point Buoy, which is fashioned after the aforementioned buoy in Key West.  But like the one in Key West, the northernmost buoy is more of a tourist photo op, not located at the actual northernmost point (the true northernmost point is about nine miles northwest of the buoy and is rather inaccessible except by boat).  All of that is interesting, but it is not relevant to the northernmost point on the US route system, because no US routes serve the Northwest Angle.  In fact, if one decides to drive to the Angle, they must pass through Canada in order to reach it.

Points of highest elevation

The US route system's highest point is US 34 along Trail Ridge Road through Rocky Mountain National Park in Colorado: 12,183 feet above sea level.  There is no sign marking the summit (nor even a place to pull off the road), but this video captures a drive along that segment:

 

That segment of US 34 is closed for most of the year.  The highest elevation along a US route that is open year-round is also in Colorado: US 6 over Loveland Pass reaches an elevation of 11,992 feet.  Six other US routes have passes in Colorado that reach elevations of 10,000 feet or more (US 24, US 40, US 50, US 160, US 285, US 550).  In fact, Colorado is the only state where US routes exceed 10k feet, with one exception: Beartooth Pass (US 212 along the Wyoming/Montana border) has a summit of 10,947 feet (also closed for most of the year).

Points of lowest elevation

Currently the lowest elevations on the US route network are in New Orleans; this map indicates that both US 90 and US 61 pass through areas of the city that are slightly below sea level:

Historically, US 99 reached approximately 50 feet below sea level as it passed the Salton Sea in California (that road has since been redesignated as state highway 86).  Lots more interesting information about the US highway system can be found here.