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?
Here is another way to ask the question: let's say you were to drive the blue route from the point on the left side to the point on the right. If you had to describe the general direction of your movement using only one of the following two words, which one would you choose: north or east? Obviously the road is not perfectly straight, but I hope you can agree that the highway generally runs east-west.
In case that is not plain to see, consider this data: the total distance along the blue line is about 60 miles. The rise of the highway (the variance between its northernmost point and its southernmost) is about 16 miles. But its run (its east-west span) is 42 miles, which is over 2.5 times greater than its rise.
Now, here are a few more details about that map: the highway shown in blue is a segment of U.S. Route 285. The marker in the lower left is at Kenosha Pass (in the mountains about an hour outside of Denver). In the upper right is the southern part of the Denver metro area. Let's zoom in on that section of the map. Note how this particular segment of the highway comes close to having a due east-west orientation:
At first glance that may seem ridiculous, but here I will briefly sabotage my own argument by stating that there is a rational explanation why the Colorado Department of Transportation (CDOT) signs US 285 as a north-south route. The map below shows US 285 in its entirety: 846 miles through Colorado, New Mexico, and Texas:
Another example is U.S. Route 24, which begins in Colorado and heads east to Ohio. The highway is signed east-west in those two states, as well as every state in between (red on the map below). But in the Toledo area, US 24 begins heading northeast and crosses into Michigan. In the Detroit area US 24 runs due north-south along Telegraph Road, and around Pontiac it even curves slightly back to the northwest before terminating. As a result, Michigan DOT signposts US 24 as a north-south route (blue on the map below):
The reasons are essentially the same as those listed above for US 41 in Miami: 1.) around the Ohio-Michigan line, US 24 ceases functioning as an east-west route and begins functioning as a north-south route, never resuming an east-west direction-of-travel; and 2.) every day thousands of drivers in metro Detroit would be confused if they saw "east" and "west" signs along Telegraph Road. Here are a few other examples:
However, as the road continues north from Fairplay, right around Kenosha Pass US 285 ceases to function as a north-south route. Instead, it begins functioning as an east-west route (blue on the maps above). And US 285 never resumes a north-south direction-of-travel. Rather, it ends in Denver, and in fact its final ten miles are on a nearly exact east-west alignment.
Those last ten miles are along Hampden Avenue through the Denver area. (Well, technically US 285 bypasses Hampden in Englewood and Sheridan, but most people still refer to US 285 as "Hampden"). The Denver metro segment of US 285 handles exponentially more traffic volume than any other section of the highway. Every day thousands of drivers come to a junction with Hampden, knowing that they want to turn either east or west, yet seeing signs only for "North" or "South" on US 285. Just a few examples:
The vast majority of drivers who turn west on Hampden do not have a destination someplace in southern Colorado. Rather, most of them have a more local destination: somewhere in the Denver area, or perhaps a bit further west, say Conifer or Bailey. Only a very small percentage are heading anywhere beyond Kenosha Pass. In other words: almost all of these drivers are heading west (not south). Ask any Denverite which direction they need to go in order to reach the mountains, and they will invariably say "west". All of this prompts the question: why should US 285 -- which heads west from Denver into the mountains -- be signposted as "South"?
It does not have to be that way. CDOT has the authority to sign US 285 as an east-west highway between Denver and Kenosha Pass. The precedent for this type of situation has already been established by DOTs in many other states. Changing the directional references along this 60-mile stretch would not impact any surrounding state, because the east-west segment of US 285 is entirely insular to Colorado. On the other hand, this change would greatly benefit untold thousands of drivers in the Denver area -- residents and visitors alike. For the overwhelming majority of people using US 285 around Denver, it would be much less confusing to have the highway signposted as an east-west route.