Mechanics:
Number of Tiles Unit can Move on Route = Greater of these 2:
A) 60 / iFlatMovement (6 For Railroad)
B) 60 * Moves / iMovement (20 For Railroad)
For unit with 1 movement, A = 10, B = 3.
Therefore, it can move 10 tiles.
For unit with 2 movement, A = 10, B = 6.
Therefore, it can move 10 tiles.
What Channel does is reduce iMovement of Railroad to 10.
For unit with 1 movement, A = 10, B = 10.
Therefore, it can move 10 tiles.
For units with 2 movement, A = 10, B = 12.
Therefore, it can move
12 tiles.
Thus, for modders, if you modified iMovement for Railroads, you have to modify channel codes to get what you want.
Else, channel may end up being OP, allowing units to move 60 tiles for instance
What it does
It places a 2nd Channel Tunnel at a coastal city of other players.
Friendly ones are considered first, followed by pleased ones.
The others are considered when there isn't any friendly or pleased ones.
Civs without coastal cities are out of consideration.
Coastal city chosen is most cultural one out of all coastal cities of chosen player.
No additional movement benefit for controlling both Channel Tunnels
Idea adopted from dacubz145