Oneway or Twoway Presignals?

Signals have two sides, in the basics part, the other side wasn`t important, since trains can`t turn back, etc. etc... But in more complex things, a badly placed twoway Combo Presignal can make errors in your network.

Part 1: The Station entrance problem with two entries

A RoRo station with two Entries

In this station the combo presignal can make errors, but can you notice why? If F-H presignals are green then Combo presignal C´s upper-right side is green too. Then if D and E exit Presignals, is red, then A Entry presignal remains green. The problem´s source is: Presignals calculates Signal Blocks, not the Possible chosable tracks: from A trough C and reach F-H platforms is impossible, but presignals CAN see this!

The Error: Signal A remains green

How to fix this? Just change the Combo Presignal C to onaway or add an oneway Combo Presignal after it, like in the next picture:

Now an Oneway Combo Presignal are added after it

With this Entry Presignal A cant look for Platforms F-H.