Grand union

A grand union is a rail track junction where two double-track railway lines cross at grade, often in a street intersection or crossroads. A total of sixteen railroad switches (sets of points) allow streetcars (or in more rare installations, trains) coming from any direction to take any of the three other directions. The same effect may be achieved with two consequent wyes if the location allows for space.

These types of complex junction are expensive to build and expensive to maintain. Special parts, sometimes made of manganese steel, are needed for each location where one rail crossed another (a "frog"); these parts often need to be custom-made and fitted for each single location, depending on the specific angle of crossing of the intersecting streets.

A full grand union junction consists of 88 frogs (where one rail crosses another rail), and 32 switchpoints (point blades) if single-point switches are not used. A tram or train crossing the junction will encounter four or twenty frogs within the space of crossing the junction.

For all of the possible tracks of a grand union to be used during normal operation, at least six different tram routes have to cross the union. In an intersection with lines oriented towards cardinal directions, these could be: north-south, north-east, north-west, south-east, south-west, and east-west.

Three-quarter unions are similar to grand unions in that they are also rail track junctions where two double-track railway lines cross at grade, often in a street intersection or crossroads; the primary difference being that one corner of the crossing does not have curved junction tracks, with the union having a total of twelve railroad switches (sets of points).

Half unions are similar, but only have curved junction tracks on two adjoining corners of the intersection, with a total of eight switches/points.

Butterfly unions share the total of eight switches/points, but the curved junction tracks are on opposing corners.

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