Hi Rich,
It's actually a lot easier and less costly to deploy layout automation in 3-rail than it is in 2-rail because we can use an insulated outside rail for occupancy detection. It's easiest to build the detection in as you lay your track. The Train Controller User Manual gives a pretty thorough description of different sensor strategies on pages 160-165.
The strategy that gives the computer the best information for maximum reliability is to use three insulated segments for each "block." To be clear, we are NOT talking about electric power blocks for powering your trains or toggling sidings. Instead, we are talking about "blocks" in the same sense as the real railroads. A "block" is a length of track, usually between switches, that can only be occupied by one train at a time. In most cases the occupancy block will be as long, or longer than the trains you run in that part of your layout. Out of the mainline that might be your longest passenger train, while is the yard it could be just the locomotive. Regardless, the idea is that your train will fit entirely within the center insulated detection section of the block. At either end you install another short insulated section that will let the computer know it needs to stop the train short of fouling the switch. There are other ways to pull off detection with only one or two insulated sections per block, but they are less reliable. We built the NWTL with three insulated sections per block and it has proved quite reliable.
However you configure your insulated tracks for detection, all the insulated sections are connect with a single wire to a detection board, such as an NCE Auxiliary Input Unit (AIU).
Each NCE AIU handles detection for up to 14 insulated sections. One wire then goes out from the NCE AIU to the common outside rail to complete the detection ciruit. Whenever the metal axles of a car or locomotive connect an insulated section to the common outside rail an LED on the NCE AIU turns on and a digital signal is generated. The NCE AIU's are daisy changed back to an NCE command station which accepts the digital occupancy signals and relays them to the PC. It's pretty easy to wire because you can put the NCE AIU's close to you track sections. You then run a standard 6-conductor telephone cable between the NCE AIU's. On the MTH York display layout my brother, Ted, and I set up detection for eight blocks and ran all the wires in about two hours. I had done most of the data entry work for Train Controller ahead of time, so we had the entire setup running with my laptop, iPads, and mobile phones Wednesday afternoon the day before the show.
