I think what you are searching for is a simplier form of http://blog.openttdcoop.org/files/blog/ ... essor1.png
found at http://blog.openttdcoop.org/2013/08/06/ ... game-2013/
There is also an older one http://wiki.openttdcoop.org/File:Psg131_Compressor.png
found at http://wiki.openttdcoop.org/Junctionary ... _and_Other
from game http://wiki.openttdcoop.org/PublicServe ... gameid_131
The first one I posted is more complicated due to being attached to a global timer as you can see in the savegame/read in the article. But it works absolutely perfectly. Note that changing to different trains will also have influence on timing so you will have to adjust at least the green timer loop which makes Sure, that all trains stop before accelerating again. Though if you split your trains into X lines so they never meet, they wont need such timing at all!
The second one is a bit simpler, does not force trains to stop always, but the top right gate is a tiny bit weird as it does not do anything (I think at least).
Combine those and you will get what you want, hopefully