Modelling splines with Blender and notepad
OMSI 2
The main thing to consider is this, if you have texture (256x256, 512x512 ...) and your spline represents, for example, a fence whose total length is 2.6m then your stretch factor in spline should be 1/2.6 = 0.384. I recommend that you model a simple plane in Blender and preview the spline.
Here is the example spline:

or you can design whole roads like this, or just part of it.

[heightprofile]
-0.05
0.05
0.1
0.1
[texture]
fence1.bmp
[profile]
0
[profilepnt]
0.05
1.5
0
0.384
[profilepnt]
0.05
0.1
1
0.384
I uploaded this as jpg, but you should use BMP.
If you need transparency on a fence or something, please use TGA (or BMP with alpha map) instead of PNG.