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A number of configurations are possible. DIAMOND The simplest and oldest arrangement consists of two Turnout s and a Diamond Crossing . Because the diamond needs to be relatively coarse, say 1 in 8, the curve radius is necessarily small, leading to a speed of perhaps 25km/h. LADDER An improved junction replaces the diamond with turnouts, which can be of as fine an angle as possible, so that this junction can carry branch traffic at high speed. This configuration assumes power operation of the points, as high speed turnout are generally not suitable for mechanical operation. The turnouts can have no Superelevation while the curve in the branch can; therefore the radius in the turnouts must be greater than the radius of the curve in the branch. SINGLE LEAD A single lead junction is used where traffic density is smaller, and moves one of the turnouts on the main line onto the branch. DIAMOND AND WIDE CENTRES A double junction with a diamond can have its speed limit raised if the track centres are widened to allow for a coarse angled diamond crossing with fine angled turnouts. |