Fixed signals are only present at interlockings, and consist of three lamps: two red and one lunar. They show a red over red aspect for "stop and stay," a lunar (white) aspect for "proceed," and a flashing lunar aspect for "proceed on diverging route" (only present on newer interlockings; older interlockings are being updated with signals that show this aspect). Tracks are divided into block sections, which can only be occupied by one train at a time, a method to protect against collisions used by most railway systems worldwide, but there are generally no fixed signals to protect block sections (signals tend to be only at beginning/end of route and just before track switches). Virtual signal aspects are transmitted to the train by a cab signaling system and displayed to the operator in the cab, as well as transmitted to the ATC system. Entry into an occupied block is prevented by an automatic train protection system (ATP), which supervises both manual and ATC operation and stops the train well before it would enter an occupied block.