I use bridge rectifiers on a dial that I can add a rectifier at increments based on the size/speed of the train. The switch is connected to 2 sections of track. Guy by the name of Dearborn Dave explained it well on another forum. Being able to adjust the values is great so you can set it and forget it and train requires full power on an up hill and power reduction on a downhill
Using handles of a zw is a bad idea and many have spoken of it numerous times on what types of bad things happen when you do this.