Ok, I think I found the problem. Brace yourself.
First, you have several phantom roads here. These happens sometimes where you place a really large and long road, it happened a lot to me when I was leveling the terrain for the Talkeetna river. They appear as 3-4 nodes long roads, not visible but messing up with the terrain. Really hard to spot, select and delete, there are often several versionq of these at the same spot. A bug, indeed.
Here is an example. This one was under the terrain, so I elevated the nodes to make them visible. Deleting this road don't make the game crash.
*
Now, the crazy part.
I don't really understand how it's possible, but all the roads you placed in this area had been duplicated in what seems like a monstrous thing from an other realm.
I started to find a strange looped version of your airfield:
As you can see, it's your airport vector, but duplicated and looped (in a really weird way, I was originally thinking there are several nodes under the ground). There is already a good runway road, but even is the vector is here, the surface is not displayed. Indeed, modifying it makes the engine crash. Same for this fake looped version of the airfield.
So I start deleting this surrogate, and notice something weird. First, it seems like there is a ton of nodes hidden under the terrain:
You see the little yellow dot, left of the city? It's the node I'm currently selecting. It's a part of the whole thing.
An other example, this time, under the middle of the city. At this point I was pressing the delete key like a crazy and still couldn't reach the visible nodes yet.
And suddenly, the kraken awakened:
Ok, this is new. At first I though you created the whole area using a single road, but it is indeed not the case, the original roads are ok and everything. But somehow, this lovecraftian abomination managed to duplicate the entire area vectors
in a single road. Of course, deleting it or modifying it creates an instant crash.
I bet it is covering a single tile.
At this point, here is what I'm going to try:
Option 1 : Going micro and try to edit the hex file for the tile, trial and error testing the area to see if I can put down this beast.
Option2 : Option 1 don't work and we need to delete this tile. It will be necessary to remake local roads (only where this thing appears), but at least you will not have crashes anymore. I can help.
This is by far one of the weirdest bugs I have witness. I bet Brano will be interested
