A points failure is a fault with the movable pieces of track or their operating equipment that enable trains to change tracks. Points can get clogged up with dirt, leaves, branches, and other debris, or they can expand when its very hot. When points fail, the system goes into fail safe mode, and trains will stop before they reach the affected points. A single point of failure (SPOF) is a part of a system that, if it fails, will stop the entire system from working.