Serbia 14 Second Invasion Serbian rail capacity

[Secret45]

Currently playing the Second Invasion campaign and was thinking about the option to redeploy some units by railway after the Austrian Invasion in the West and South starts. But I realized currently (almost 20 turns into the campaign) my rail capacity is at a value of 0. 

This will obviously make the railways way less of a factor then I anticipated. So I wanted to ask if anybody has already played the campaign and nows if the Serbians will get rail capacity a while into the Scenario? If yes how much is it and roughly how far into the campaign will it become available?

It would be really important to know in order to plan the further moves for some of my units.