A Single Point Urban Interchange (SPUI) is a type of highway interchange, and is obviously my favorite. It is also known as a Single Point Interchange, Single Point Diamond, or Greiner's Urban Interchange. It is like a diamond but with a single traffic light in the middle. This allows concurrent left turns. The freeway can go over or under. The base SPUI has 3 traffic light phases (known as a SPUI3). A SPUI can also incorporate one-way frontage roads, making an extra phase (SPUI4). A SPUI can be considered as an upgrade from either a diamond or an at-grade interchange. Another advantage is that it requires less right-of-way than a standard diamond or parclo. The first SPUI in the US was built in Clearwater, FL on US 19 at FL 60 by Greiner Engineering of Tampa, FL. It was designed by Wallace Hawkes, the "granddaddy of the urban interchange". It opened on February 25, 1974. The second SPUI in the US opened on September 9, 1975. It was built on I-74 at 7th Av in Moline, IL. However, the idea of a SPUI started before this. In 1960, Caltrans proposed an "inside-left turn" interchange for Palo Alto, CA, which was probably to be a SPUI. A SPUI was built in Cologne, Germany by the Rhine River by 1975. If you want more info on SPUIs, the book Single Point Urban Interchange Design and Operations Analysis by the Transportation Research Board is very good. It may be at your local university library. Return to SPUI's SPUI list See Dan Stober's page on the construction of SPUIs in Salt Lake City