The road surface is very blurry in the distance,I don't know why,What should I do, thank you

This is caused by texture streaming. When textures get sow low res at such a short distance it might be because the streaming pool is full.

you can check your current pool size by inputing this into your console r.Streaming.PoolSize
and set it later to a higher value with the same command followed by the number you want the pool to be “r.Streaming.PoolSize number”.

The reason for the pool being filled might be be:
a. Your graphic settings are too low.
b. You have too many textures with too big resolutions.
c. Your graphics card does not have enough memory to load all the textures for the setting you are using (try using a lower setting).

You can also try and check the lod level for your street mesh, maybe the LOD is too agressive.