What are highway mileage signs based on?

Factual Questions
1

This came up during a conversation at work. Someone said that the mileage signs on highways are based on the distance to the City Post Office. Living in Dallas, I asked, “Which one? What if the Post Office changed location?” The conversation fell apart at that point with too many what ifs. I thought that the signs referred to the distance to the center of the city, but even that is questionable. How is the city center determined? Houston, for example, sprawls unevenly, in multiple directions. So, basically 2 questions: 1. To what point are highway mileage signs referring and 2. How is the center point of a city determined?

2

We had a thread on this very recently and the general answer is that the point that is defined is usually the town hall rather than a post office (which makes sense).

3

The story I was told many years ago was that the signs gave the distance to the main post office, which in many cases is quite near the city hall. However, in Dallas, it probably refers to the old Terminal Annex building at 207 E. Houston St. - right next door to the “Old Red Courthouse”, the original Dallas City Hall.

I do not have any cites for this, but it was told to me by my mother about 40 years ago, and has been borne out in those cases where I’ve checked it. YMMV :smiley:

4

WAG here: I’ve always assumed that it is actually the distance to the exit. My experience tends to support this. In cases where more than one exit, I have no decent guess.

5

Based upon my personal experience, the signs were placed wherever the forman told us to put them. He would, of course know the exact distance to City Hall, or the County Courthouse, whichever was appropriate.

Sgt Schwartz

6

I looked for a thread on this subject before I posted this one and I could not find one. If you could point me to it, it would be helpful.

7

I didn’t really mean the signs that read, “5 miles to US 35 Exit 22,” for example. I really meant the signs on the side of the road that list the next few upcoming cities and the distances to those cities:
Dallas 5
Podunk 25
Houston 255

8

Here’s a link to the thread.

9

Here’s the recent thread, for reference.

10

There is a small town I drive through from time to time. As you approach the town there is a sign that says, “SmallTown 5 miles”. Driving another 3/4 miles toward the town there is another sign that reads, “SmallTown 6 miles”.

11

You were obviously driving on a treadmill.

12

But did he take off?

13

I haven’t seen anything quite this obvious, but I have noticed that the “point” is not always the specified distance away.

For example, if I’m driving along and I see a sign that says “Anywhere 25,” I typically glance at my odometer and add 25 to whatever I see, which should allow me to use the odometer to estimate my distance from Anywhere at any point on my route. (Specifically, if my odometer says 1000 when I see the sign, that means that my odometer should be close to 1025 when I arrive at Anywhere. If I glance at my odometer later and see 1010, that means that Anywhere should be 15 miles ahead.)

But no, this does not work. There is usually a 3-8 mile difference. In the above example, I am quite likely to glance at my odometer and see 1010 just as I pass a sign that says “Anywhere 18” or “Anywhere 12.”

This happens frequently enough that I am led to believe that the point used to calculate distance from point A on the expressway to Anywhere is fluid and moves around quite a bit.