 The signal arms usually all stand in the 'clear' position.Although trip wires working with colour light signals are occasionally used alongside railways in the vicinity of airports, and are common in railroads running through the Rocky Mountains and similar areas around the world, the remarkable thing about the Pass of Brander system is its age and the fact that it is entirely mechanical in operation.The system is sometimes referred to as 'Anderson's Piano', after its inventor and the noise that the tensioned screen wires are said to make in the wind.