Judging from the content, It looks like you want a real time solution with a basic material. If this was for arnold or offline rendering, there are '3D' maps like noise that could get you some convincing dirt.
For the real time case:
- Add a UVW Unwrap modifier to your mesh. Turn on selection mode (not select and move, this can get annoying otherwise)
- Enter polygon mode, and select all polygons for a given section of road. Helpful tip: Ctrl click = add one, Alt = Remove one.
- Choose the planar 'quick planar project' icon. You'll see a preview, and likely you'll want the z-axis. You can find out where this is in the help guide.
- Now, all your selected polygons are mapped to a UV space that is like looking at them straight down.
- Open the UVW editor and go into polygon selection mode again.
- Select a few of the polygons, and scale/rotate/adjust vertices to match your texture atlas.
- Keep doing this over and over until complete.
Note that this is workflow for the atlas I see in your example. There are other ways to do this.
Create a single section of dirt road. Say, 4m x 4m. Set up UVs like above for this one section, and lay down these segments. When done, merge all the meshes and weld similar vertices. Later, go back and add decal meshes to add some uniqueness to the road.
If you know anything about shaders on your target platform, you might want to make a 2 or 3 layer shader that has different textures that repeat at different frequencies and phases. This can also be set up in max for preview purposes. Doing this you can have a road that is more unique, instead of something that repeats over and over.
Getting more advanced, it's also possible to build road meshes from splines using MCG or python, I think there is a tutorial for this on the 3ds Max Learning channel. When the road is constructed, it could be set up to compute the correct UVs along the road.
The main idea in all of this, there isn't a magic 'Make this a textured road' button. It takes a decent amount of labor to add good UVs a mesh. If you set up an atlas properly or are able to use multiple textures, then your job can get a little easier using texture repeats/wrap/mirror.