Prior to I-25, there was a different main highway that connected Denver to several of the Northern Front Range cities in Colorado.  The number of this highway has changed a few times during the past century, but its general corridor has remained the same: it still runs through Ft. Collins, Loveland, Berthoud, Longmont, Lafayette, Broomfield, Westminster, and Denver.  Not all of those cities had even been established at the time of the 1916 map shown below, but the highway corridor running along the Northern Front Range is readily apparent (going forward I will refer to this road as the NFRH, for "North Front Range Highway"):

Our planet is spheroidal in shape, which means its surface is curved.  So making a map of the Earth's surface involves taking something that is curved and projecting it onto something flat (such as a piece of paper or a computer screen).  But this flattening inherently causes some distortion from reality.  It is not possible for any one map projection to preserve all of the following: 1.) direction, 2.) shape, 3.) area, and 4.) distance.  So when a cartographer chooses a particular map projection, they are choosing to preserve one or more of those traits at the expense of others.

Lots of people (myself included) have an odd fascination with the superlatives of just about any topic.  As it relates to highways, a common question is "What is the longest US route?"  (answer)  And then related questions branch off from there:

• What was the longest US route historically?  (answer)
• What is the longest north-south US route?  (answer)
• What is the longest 3-digit US route?  (answer)
• What is the longest 3-digit US route that runs east-west?  (answer)

Eventually the questions start swinging around to the opposite extreme, and those are the topics of this post.  Specifically we set out to answer these questions:

• What is the shortest US route?
• What was the shortest US route historically?
• What is the shortest 2-digit US route?
• What was the shortest 2-digit US route historically?

Currently the longest single-state mileage of any US route is 893 miles (US 83 in Texas).  Historically, before US 101 was truncated to Los Angeles, that route was undoubtedly the record-holder: the California segment of US 101 was about 941 miles (give or take a few, depending on which year, since the alignment changed many times and in many places). 

Historic US 99 in California was the second-longest route through a single state, although its mileage is even more difficult to measure, since it was replaced by I-5 in many areas, and as a result some segments of the original route have been vacated.  The Historic Highway 99 Association of California offers a length of 917 miles.  Although that page does not specify a year, I am sure that figure is reliable, since my own back-of-the-envelope calculation yielded a similar distance.  (Note that drivers choosing US 99E between Sacramento and Red Bluff had to travel 2.2 miles further than those who chose US 99W.)

Thanks to this blog post, I recently became aware of "the Palm and the Pine" along what is now CA state hwy. 99, just southeast of Madera.  In the median of the highway, a palm tree and a pine tree are planted side by side (one representing southern California, and the other representing northern California):

US 96, US 14, US 75, US 99, US 240, US 42, US 138, US 360, US 431, US 380, San Antonio NM, Astoria, US 650, US 28, US 113, Crescent Jct, San Angelo, Long Beach, US 270, US 412, US 277, Springer, Trinidad, US 41, US 99, US 130, US 209, Toledo, Cleveland, Cumberland Gap, Cincinnati, US 91, US 75, US 175, US 80, Louisville, US 601, US 167, US 111, US 97 ​

The other day I was driving north on C-470, and I wanted to go east on the 6th Avenue Freeway towards downtown Denver.  That movement is shown on the map below:

I rarely drive that direction along C-470, but I have lived in Denver for a long time, and I'm pretty confident about knowing my way around.  So as I approached, I was quite certain that I would need to follow eastbound I-70, and that the exit for eastbound US 6 would come up shortly after that. 

​But then I saw this: the first sign that references US 6 on northbound C-470:

The photo below was taken looking east along the international boundary between Canada (to the left) and the U.S. (right).  The large structure (with the flags on top) is the Peace Arch, which straddles the border.  (It is not square to the boundary line; rather it is situated at a slight diagonal that roughly matches the angle of the roads that run through here.)  If you look closely, you can see three boundary obelisks in the foreground:

I am about to ask a simple question.  It is not a trick question, so no reason to over-think it.  The map below (like most maps) is oriented with north at the top.  You might not be able to make out much detail, but that's ok, because all I want you to do is take a look at the highway shown in blue.  And the question is simply this: does this highway run north-south?  Or does it run east-west?

US 87 and US 287 converge in Dumas, Texas, and share about 49 miles of pavement down to Amarillo, where the two routes separate again.  ​