Before I get into this I should emphasize how much precision is required if you want to make it look good. Think of it as a construction project: the end result depends on planning things ahead of time.



In these examples I will presume you have some basic knowledge of road networks. For those completely new to this I will summarize the most important tools.

Assets involved:

Railway Trench 4x
https://sp.zhabite.com/sharedfiles/filedetails/?id=543610836
Railway Tunnels
https://sp.zhabite.com/sharedfiles/filedetails/?id=543811162

Boformer's Sunken Stations
https://sp.zhabite.com/sharedfiles/filedetails/?id=538157066
[+ Extra Train Station Tracks]
http://sp.zhabite.com/sharedfiles/filedetails/?id=515489008

Mods required:
Terraform Tool 0.8
https://sp.zhabite.com/sharedfiles/filedetails/?id=411095553

And/or
Extra Landscaping Tools
https://sp.zhabite.com/sharedfiles/filedetails/?id=502750307

Useful:
No Pillars v1.1
Advanced Road Anarchy
Fine Road Heights
Precision Engineering

The first tool in 0.8 allows you to raise or lower the terrain cell by cell. This makes it perfect for creating trenches, because it will create them at a precise depth (rightclick and drag for -12 meters).



Next to it you will find a more general purpose bump tool. Extra Landscaping Tools gives you a lot of brush size and shape options from the map editor which is always useful.



Third is the smoothing tool. Not much to explain there. Smooth criminal.
Then there's the flatten tool (fourth in TT, second in ELT). You will need it a lot in a lot of situations. Right-click to select the height, left-click to flatten.

You can also use the ramp tool and any other tools provided, but these are the essential ones.

To show you how you can use the assets in a modular way, I will be creating one gigantic trench that could run through an entire city. I will use some improvisation along the way.



Starting out, and this is probably the most important step, we will want to flatten a large enough area. We will need a lot of space to do this. I recommend focusing on the lower level first. This should (ideally) be 12 meters below the rest of your city, or 24, 36 etc if you want to stack and terrace assets and use default 'steps'.



Your layout does not have to be final here, just give yourself a rough template to work with.

With our construction zone ready, we have to build a road grid. The zoning cells are extremely important and should be used whenever possible. Let's build roads on the side of the trench first.



Generally you can't build roads in close proximity to each other because of snapping / collision. So going road by road, track by track is the way to go.



Here I have built some large sections. If you want any bridges to run accross, you'll want to leave space between the walls (2, 4, 6 cells).

At this point you may notice small bumps in your terrain. Remove the assets and roads involved, flatten the area and rebuild, or your trains will sink through the floor and it will not look as good as it could.

We can transition to underground tracks or sunken stations using tunnels, which I will cover later.



Curves and bends are possible but most assets don't play well with them. So it helps to create some hidden 'hubs' where you can submerge intersections without having to create complicated wall layouts.

At this point you will want to wait a second and think twice before you move to the next steps. It can be very hard to replace parts later without having to redo large sections.



If you are happy with your layout, you can start replacing the roads with train tracks.


We need roads at the end of our trenches to hook up our tracks, adjacant roads and later on bridges. If you lose your grid by demolishing too much it's your own fault, don't blame me or the game. :D

Now you can slowly start tweaking your network and the terrain. It can be hard to place tracks directly next to each other, so sometimes you will have to drag them in from outside the initial build area. Another reason why I emphasize not to remove all your roads at once.




With everything placed, it is safe to go all the way to the edge of the trenches with the flatten tool.







It helps to go back in and flatten the lower level even if it already looks flat.

I'm starting to expand the roads outside of the initial build area. This allows for early connections with the rest of your city, but more importantly, bridges!



Make sure you trace roads on the same grid, that will give you the best end result and prevent collisions with the walls.



If you are having issues creating bridges, please refer to the section 'Bring in the Dozers'.

Congratulations, the bulk of your work is done! Now you can start decorating and interconnecting your network.



Tunnels are kinda iffy, so I left those for last down below.

Very short tunnel entrances can cause some glitchy situations, which is why the assets kind of hide any gaps. It helps to tweak the length of the tunnel entrance as well as the terrain you are intersecting with.



A very short entrance might work, but sometimes a smooth long one underneath a large avenue bridge can actually look better. The entrances require a lot of trial and error, again don't blame me for wonky stuffz, it's just the mechanics of the game. No Pillars and Advanced Road Anarchy can really help out.



Ideally you get an 'at-grade' connection, meaning the tracks themselves are flat where the ground is angled. If all else fails demolishing and having a second try works wonders. :)

Okay everyone, that's all for this guide, thanks so much for reading all that! (Yeah I know you didn't :D) If you have any further questions hit me up or leave a message down below!

I will leave you with some more pics...

I often get asked the same questions, so here are some answers to the ones I see the most.

No. If you are impatient or want something that only requires the click of a button, this is not for you.

You snap them to the last cell of a trench. If you place them in the correct spot, they work like an endcap. They are not free-to-place, they work like any other roadside asset.

Not likely. I would rather avoid them because of collision and viewing angle issues.

Oh yes it does! But the assets above are not intended for them. I'm planning to create other meshes for road trenches. Until then, please use other sunken wall assets.