A passing loop (also called a "passing siding", "crossing loop", or colloquially "a hole") is a place on a single line railway where trains in opposing directions can pass each other. Trains in the same direction can also overtake, providing that the signalling arrangement allows it. A passing loop is usually double ended and connected to the main track at both ends of the main line, though a dead end siding, which is much less convenient, can be used.