Built my first Nether Ice Highway and ran into some issues.
1. When you put stone buttons on top of the Ice blocks, your boat slows down like it was sitting on a stone block.
2. When you have an ice block in the center and a slab on either side of the ice block, but on the lower half of the space on either side of the ice block (so there is nothing but air to the right and left of the top of the Ice block, the boat still thinks there are stone blocks on either side and you move slowly.
3. My only solution was to mine enough Ice blocks to make a path three blocks wide to get it to work.
4. Putting glass blocks or glass panes on either side of you, does not keep you in the center of the three block path, you cruise right through the glass as if it doesn't exsist. This means, making a glass wall at the end of your Ice road has a chance of sliding you straight through the wall and into lava on the other side.