Many people have asked how to wire a reverse loop. This video shows the easy way, using common components you probably already have.
Two Power Supplies
Kato 24-816 Insulated UniJoiner ($5 per pack)
Kato 24-827 3-Way Extension Cord ($5)
All of my layouts have more than one track. Since everything I do is DC, I need a separate power supply for each track. Taking advantage of multiple power supplies, I wire the reverse loop to a power supply from a different track. This avoids shorting out the power supply and eliminates the need for a double pole double throw (DPDT) switch.
The illustration above shows a two loop track with a reverse loop in the center. A Kato 24-827 3-way extension cord is used to connect the outside track and the reverse loop to the same power supply. This setup permits using the reverse loop without stopping the train and changing the polarity of the inside track while the train is still in the loop. If the outside track is going counter clockwise, enter the reverse loop at the top. If the outside track is going clockwise, enter the reverse loop at the bottom. While the train is in the reverse loop, reverse the polarity of the inside track. The train will exit the reverse loop going in the opposite direct and the polarity of the inside track will be correct with no chance for a short.
Genius! 🙌🏼