Lego GBC Interactive Modules
Lego GBC Interactive Modules add a whole new layer of fun to a GBC layout, they vary from normal modules in that they use public interaction in order to move balls through or modify the path of balls moving through a module.
The public drives dozers around a pit in order to push the balls into the next module.
These modules need a lot of balls to work effectivly, this typically involves adding at least 100 extra balls to a layout, however, depending on the size of the dozer pit, you may need as many as 500 extra balls to make the module more fun.
It is recomended to add a metering module like Lego GBC Reservoir Lift in Yellow immediately afterwards to smooth the flow of balls from the module.
It is also worthwile adding a bypass mechanism for when there is no one driving the dozers.