Glitch in the matrix?

Sunday, March 23, 2025 • misc

Just to manage expectations - it is probably explainable, how such things happen in the real world. But it’s nevertheless something strange, if you take signposts seriously.

So, first things first. Let me explain the situation: In Munich there is an underpass in Berg am Laim, that goes below the railways. In the last year or so, this underpass has been a bit refurbished and new signs have been installed.

The signs that have been added show the shortest exit way. That’s probably a new regulation that such signs need to be installed and glowing if the underpass has a certain length and could be considered a tunnel. This underpass is probably the gray area, as you can see the light at the end of the tunnel already. So it is not very long.

Anyway, here is the sign at the beginning of the tunnel:

As you can see, it has been added after 20 meters and you can exit the tunnel to either side: The nearest exit would be 20 meters away, the other end is 150 meters away. That allows you to deduce that the total length of the underpass is 170 meters. So far, so good.

After another 30 meters, you see the next sign:

We see, it says either 50 meters or 120 meters - in total 170 meters. Still makes sense, no problem so far.

But wait, until we walked another 20 meters to the next sign:

Here we can clearly read, that the exit is either 70 meters or 90 meters away. In total our tunnel is now 160 meters long. It shrunk 10 meters. Interesting. Between the last sign and this one the tunnel lost 10 meters. Good for us, who want to go to the other side, we need to walk 10 meters less.

Let’s see, how it goes on. After another 20 meters, we see the next sign:

It says 90/70 meters, which is in total still 160 meters. As we see from the numbers, we passed already more than half of the tunnel. The far end is now nearer.

Let’s walk another 30 meters to the next sign. But wait, what does it show?

It says 120/50 meters, in total it’s again 170 meters. It seems we left the weird area, when we were pleased already that we need to walk 10 meters less. The tunnel is back to its original length. That’s very strange.

Just to be sure, let’s walk to the last sign, 30 more meters:

It says logically 150/20 meters, in total 170 meters. All makes sense.

Just to double check, let’s walk in the same direction but on the other side of the street and observe the exit signs there:

The right side seems to be more consistent: It just expands 10m from one end to the other. Interestingly, the tunnel seems to be 10m longer on the left side than on the right side.

Another look at this right side of the tunnel reveals another strange thing: The pictures are taken in order, so you should expect, that the distance from one end (where we started) is strictly monotonically increasing, while the distance to the other end (where we are heading to) is strictly monotonically decreasing. The figure on the sign should always look into the direction of the nearest exit. The distance to the starting end of the tunnel is: 10m, 40m, then suddenly 90m, then back to 70m (I definitely didn’t walk backwards…) and then jumping up to 120m. Something strange is happening here.

In summary, this tunnel is a very interesting construction: If we use this effect on purpose for other tunnels or maybe even streets, we could save so much time. Just shorten the distance in the middle of a route and we’ll be faster arriving at the destination. Nice.

There’s a catch though: If you travel in reverse direction, the length of the tunnel might be longer. Which gives the routing algorithm another way to optimize routes.