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Compact SPUI (Underground)

mathematically sound sunken-highway spui (whole integer units!)

highway is x axis
road is y axis

asset is 40 units wide, 28 units tall
excluding ends, intersection is 30 units wide and 20 units tall (measured from node to node)
highway ramps are 2-lane one-way roads that are 10x3 units.
connecting to the road are ramps at 45° angles, 5x5 units.

highway uses the standard spacing (as used in the vanilla cloverleaf), and is at a depth of 12m.

if you use any of these spuis properly along with a carefully-constructed highway system you should be able to maintain a perfect grid with no wasted space or funny angles!