Hey there, welcome to this humble guide. The information on this guide may become out-dated as time rolls on by, so be sure to double check any software versions this guide may recommend. The version numbers may become out-dated, but the core method should continue to work. In the case this is no longer true, the guide will be updated.

Before we get started there are some things you will need.
Unturned's current unity version. Download Unity Hub, and install a Unity 2021.3 version. Not all versions will work, and generally older versions of Unity will work fine for this.

You also need Nelson's Bundling tools, you can find these in Unturned/Extras/Sources/. These will be in a Unity Package called "Project", drag that in and import.
You will need a image editing software, PaintNET[www.getpaint.net] or Gimp[www.gimp.org] are great freeware tools for image editing, but anything will work.

The Standard for roads is ether 64x64 or 128x64, try to reflect this when creating your roads. Bellow are some examples. This is not a hard rule, you can make your roads any size you want, but it is recommended to stick to a power of 2. Some maps opt for extremely small texture sizes on their roads in order to reduce file-size, taking advantage of looping.






Assuming your Road textures are already made, lets get started with the Unity work.
All you need to do is import your images, put them into a folder and then give them these settings. You can change the Filter mode to whatever you want, Trilinear and Point No Filter are the ones you'll want to pick between. (Trilinear is better the Bilinear, didn't know that at the time I wrote this though.)

Now you just need to Bundle, bundle it under YourMap/Environment and name it Roads.unity3d.
One thing of note is that Unturned seems to have a limit to how many roads you have to have. You must have at least 10 roads, if you have no ideas what roads to add to reach this number, feel free to just add a ton of 1x1 pixel filler roads. (This may have changed as of recent, not check in a few years)

Thanks for reading, make sure to notify me if there's anything wrong with this guide!