That controller is made for negative polarity. If you want to change the direction that the cars will run you could just switch the wires at the power supply, but that would also change the track polarity and the controller would no longer work. Possibly it might be damaged. If you want to change the direction that the cars will go you can switch just the wires that go to the track rails. If you were going to do that often it would be nice to put a DPDT switch between the controller hookups and the track rails, you would need one for each lane. The schematic shows a positive polarity track with a reversing switch, a negative polarity track would be the same except that the wires would be reversed at the power supply.
Commercial 1/24th tracks are almost always wired for positive polarity, so I believe that the first electronic controllers were made for those. When club 1/32nd racing became more popular I expect that people wanted to use their electronic controllers and wired their tracks for positive polarity. Whatever the reason all of the tracks that I have run on for many years were positive polarity. I did run on one HO track that had some lanes wired positive and some wired negative!
When you buy a modern set those have modular hookups, so you don't have to worry about mis-connecting anything, but that makes it difficult to use a better power power supply or aftermarket controllers.
