I have previously posted about this issue being a bug, but it was ruled not a bug and hence why I am posting it here. For reference here is that bug report: viewtopic.php?f=23&t=31949
The issue is that due to certain ways in which biter path-finding works biters can be prone to taking out power poles along rail lines and it has only become an issue post the 0.13 patch. Why? Because previous to v0.13 the common method of defending against the biters was the use of 'victory poles'; these were items that could be dropped in the world (a simple wooden chest for example) and would disable biter spawning in the surrounding 3-4 chunks. Whilst this method was effective it was most certainly overpowered and more or less negated the threat of biters to the player and buildings.
So in 0.13 this mechanic was changed such that biters might expand to a given chunk based on a probability mechanic - if the player had more structures in that chunk the lower the chance of biter expansion. This made 'victory poling' useless and as such the biters have now become a real threat again; forcing the player to properly defend his structures with the use of walls/turrets.
First and foremost let me say this: I completely agree that victory poling was overpowered and very much welcome the changes that have taken place to stop this mechanic, I do not think that it needs to go back to the old 'victory poling' way.
However, it has had a rather serious consequence on the way that players must approach megabase sized worlds. Previously the player would not have to defend outposts and/or rail lines, however this is now a necessity. Defending outposts makes total sense and I strongly feel that this is now ballanced - the player must protect his investment. However, the defending of rail lines is a large issue. Rail lines can often extend great distances (especially in RSO maps) and most players will run a power-line down these rail lines to supply outposts with power.
Here's where it gets tricky - biter path-finding tells biters to attack sources of pollution and since power-lines and rails are not sources of pollution they are normally left alone. However, if a large group of biters path over a large power pole when they are on their way to attack a source of pollution (an outpost for example) they can sometimes get stuck. If they get stuck they will attack whatever is in their way - in this case the large power pole. This can have devestating consequences as there is potential for entire sections of worlds to lose power due to this.
Here's a nice gif which demonstrates this issue happening:
GIF
So what can the player do? Well, to ensure 100% protection they can wall and turret entire train lines. This does work, however it is extremely detrimental to the game-play experience. Why? Because doing so is just not fun when you have to wall and turret massive sections of the world. It is an extremely laborious task even with the use of blueprints and helper mods such as FARL. Furthermore, to ensure that these turret walls are maintained you need to setup roboport networks with supply trains - with a different roboport network if you want to change direction as to avoid construction bots pathing over biter nests.
As someone who has spent 3k+ hours in the game and built multiple megabase sized world I believe this to be a massive issue in the game at the moment. In my current megabase I have spent enormous amounts of time doing this turret and walling of the train lines and it is really taking away from the fun of the game - I want to be out building outposts, launching rockets etc.
The proposed artillery/combat train I do not think will be able to combat this issue as it would be by chance that a train was passing as the biters were pathing over the rail line.
I have not put much thought into possible ways in which this issue could be addressed, however thought I would make a post here to see if any other players are experiencing this issue - particularly those who have made megabase sized worlds also.
