Here is a layout for 3 running trains (with a 4th train in a siding), which is 4'10" by 11'10". Three trains can run at the same time in the same direction if short trains of 6 or 7 cars with engine and caboose. This picture shows three running trains, two steam and one diesel, with a fourth steam train with tank cars in the siding waiting for its turn to swap with one of the other running trains. The crossing in the middle is the thing to watch out for, the trains need to run at the same...