This is a small layout that took about 15 minutes to setup. All the track needed is in the picture below. It is a fun layout that permits two trains to easily travel between the inside and outside lanes. The inside track has the reverse loop. In the video, the direction of both trains is changed and both trains end the video going in the opposite direction as they started.
When creating a reverse loop in a DC track, there must be two separate electrical circuits. About half way through the reverse loop, I inserted two insulated Unijoiners in the track. The turnout closest to the loop determines which side of the loop gets power.
You will notice the train moving very slowly when it passes the insulated section. This is because the wheels on each car short out the loop for a moment as they pass over. I have not found an easy way to prevent this without isolating a whole section of track and adding a double-pole double-throw switch for that section. At low speeds, the power is low enough that the circuit breaker in the power supply is not tripped. At higher speeds, and subsequently higher power, the breaker continually trips. Take the reverse loop slow, and it will work just fine.
Download the SCARM layout file here.