Oh, the terrain glitches... Yeah, those can be extremely annoying.
If you encounter any, it's best to momentarily quit to menu and log-in again. This should solve those terrain glitches.
Should these glitches be widespread and occur frequently, I'd recommend to see if the Video Drivers are up-to-date and that the GPU isn't overclocked or anything (really funny stuff can happen if the GPU produces errors calculating the Terrain).
Trying to operate the SRV over such bugged Terrain can quickly turn into a "Driving nightmare".
If that doesn't help, playing with (i.e. reducing or increasing) the "GPU Terrain Work" slider might help.
