Public tranportation (e.g. non drivable railroad and runway) are usually set to level -5.
When altitude is shown in the app, this makes these "discrete" from the drivable roads. And it is said to prevent interference, when a driveable road is crossing or is close and parallel to it.
Hope that's clear, I shall put it in the road type table @ the editing rules.

Well they don't really "need" work. They're runways..
I see dozens of unfinished segments you've created in December. Better focus on that. It's driveable. When I'm at a pc I'll have a look at the runways

send from my SGS4, using Tapatalk

I still need an unlock. It's locked at lvl 3 and Im a 2. Work in that area needs to be done.