Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Coast Landscape Racing Track Free.
Coast Landscape Racing Track v1.5
This package contains a coast landscape usable as racing track or a first person action game.
The scene is only basicly decorated. With the lates version we added some trees to the scene.
Collision-Meshes for walls and ground, skydome and all textures are included.
Perfect scene for prototyping and gameplay testings.
Textures-sizes between 1024×1024 to 4096×1024.
The scene is not(!) created with the Unity-Terrain.
Total Polycount about 150.000
Works with Unity 5, 2017, 2018.