Single-point urban interchanges (SPUI) were first constructed in the early 1970s, and are used most often in tight right of way situations. Their primary feature is all four turning movements intersect at a common point. They are costly to build because of the large bridge structure that is required.
How do single-point urban interchanges decrease congestion?
Let's compare two designs:
- In the diamond interchange, the streams of left-turning traffic cross each other. Traffic signals on either end can keep turning vehicles from clearing the interchange. It may take several traffic signal cycles for a vehicle to make a turn and then leave the interchange.
Single-Point Urban Interchange
- In the single-point urban interchange, the streams of left-turning traffic do not cross. Opposing left turns can be made at the same time; with only one set of traffic signals, more vehicles can make the turn and clear the interchange in one traffic signal cycle. SPUI also allow for long, gradual turns. Larger vehicles like trucks, buses and recreational vehicles have more room to navigate. Traffic moves more smoothly and everyone can breathe a little easier.
What about pedestrians and bicycles?
The single-point urban interchange is very safe for pedestrians and bicycles. The pedestrian path is well marked through the use of curbs and medians, different colored materials, or through the use of more substantial structures.
Why are single-point urban interchanges more efficient?
A SPUI moves more traffic through a smaller amount of space. Compare to the cloverleaf design, which takes up a much greater amount of land. The SPUI design makes it easier to build new interchanges within existing state property.