https://www.youtube.com/watch?v=mlSFGs2TlSo Not sure how Pole Position does it, but this is hysnc (int) with a prescaled set of tiles, and changes the map mid line for gradient with the subpalettes, going down the screen. Pretty much like the effect in Contra Hard corps with the Giant running robot. Of course, Chris made a map system to design different tracks.
The title screen transparency effect is a nice twist on a few tricks, through; combining the XOR pattern switching effect at 60hz, but putting a layer between two other layers - everything in between shows through the alternating XOR pattern, which otherwise shows as solid.