The Single Point Urban Interchange (SPUI) is a variant of the standard diamond interchange and was first constructed in 1970 to improve traffic capacity and operations while requiring less right-of-way than the traditional diamond interchange. A SPUI is a grade-separated interchange design where all freeway ramps begin or end at a single signalized intersection on the arterial.
The design allows for left-turning vehicles coming from opposing directions to turn simultaneously, without crossing paths. This enhances safety by reducing the number of places where vehicles cross paths and improves efficiency by allowing more vehicles to drive through the intersection during a signal cycle. Right-turn movements onto and off the freeway ramps are guided by stop or yield signs, away from the main intersection. A SPUI can be designed with the freeway passing over or under the intersection. Pedestrians use marked crosswalks to safely cross the freeway ramps, and bicyclists may use pedestrian paths or follow the flow of traffic.
