Where to put Blocks

4 places:  Between each set of switches connecting each loop.  If you are running a command system on a layout this small, you do not need blocks.  If you are running conventionally, you would be wise the divide each of your loops into four blocks each. 

Attached is both a PDF and JPG of the layout.  

Thanks very much for the input.  

If you will be using MTH's DCS system, I believe the recommended practice for block size is 10-12 track joints. Following that practice I would break each loop into at least two blocks. Four blocks as suggested above for conventional operation would also be fine.

dag posted:

Hello All: 

I'm new here and I am helping my son with his Lionel Train hobby.  We've set up the layout on the attached file and he would like to run different trains on each loop (three trains at any given time).  It looks like the use of blocks ought to work based on what I see in other posts.  Any advice on where we should put the blocks to isolate each loop?  We are driving these with the typical transformers you get with complete Fastrack Train Sets (Hogwarts, Polar Express, etc.)

Thanks in advance for any help.   

You have three interconnected loops to run three trains simultaneously but there's really not much variety of operation. There isn't enough track for three trains to re-route around each other in opposite directions. I suggest you consider reworking the track plan before you get too involved with wiring.

Conventional operation with block control for multiple trains will be cumbersome unless the track plan is designed to minimize the number of blocks that will allow a variety of train routings.

As drawn, the tracks at the sides have only 2.5" spacing center-to-center; trains are likely to collide.