For 1/32nd and 1/24th tracks the positive rail should be on the right looking in the direction of travel. Track polarity refers to the direction that power goes through the controllers. If you are using resistor controllers the power can go either way, so track polarity is not an issue with those. If you want to use electronic controllers you have to be careful. Most electronic controllers only work in one direction. All 1/32nd sets are wired for negative polarity, most club tracks and commercial raceways are wired for positive polarity. Some makers have controllers for either polarity. Here is a schematic for positive polarity. If you try to change the direction that the cars will run by switching the leads at the power supply you will also change the track polarity. In order to change the direction of travel without changing the polarity you have to switch the wires that go to the track rails.
