Can a player move an active knight from one point on his road section to another point if an opponent's knight occupies an intersection between those two points? In other words, is there anything that prevents you from moving your knight past an opponent's knight (obviously, you're not displacing it)? I don't think it's prohibited by the rules...but it seems funny to me that it would be permitted. (You'd think the two knights would fight each other to the death!)
You can only move your knight along continuous roads. An opponent's knight interrupts your continuous road (which is why you can lose longest road); this also means you cannot move your knight past an opponent's knight on the road.