In my scene, the effect of the road edge isn't same. For example, the left side is normal, but the right side has mosaic distortion, when the camera move near. I change the mipmap setting and anisotropic setting in unity (even use the ansio level 9), but it doesn't solve the issue. You can have a look at the issue in following picture,

Note: the picture is a snapshot of my right side of one road, on the opposite position, the fence and grass ground is ok. And, the picture used for both fence and grass are tiled.

Hope someone can tell how to solve this problem in unity. Thanks.