Grade separation carries crossing roads over and under one another so traffic need not stop, with curving ramps connecting the levels. The first cloverleaf interchange in the United States opened in Woodbridge, New Jersey, in 1928, drawing on European parkway and autobahn practice. Such junctions were essential to high-speed limited-access motorways and consumed large areas of land where routes met. Their sprawling footprints reshaped the urban fringe and concentrated development around exits.
The free-flowing interchange made the motorway network possible, but its vast land take and severance reshaped city edges around car access.
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