> Tunnels have a smaller height difference than bridges. Only need clearance for the height of a cyclist, not for trucks or trains plus electric lines.

Well, sure. Tunnels built FOR BICYCLES ONLY will have this advantage. A bridge build FOR BICYCLES ONLY would have similar small height requirements so this seems kind of moot.

Seems that the rest of the ideas are mostly based on the same one; smaller inclines/declines. The "work first, then coast" is not, of course.