Innovative Intersections and Interchanges

 

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Single-Point Urban Interchange (SPUI) icon
Innovative Intersection: Single-Point Urban Interchange (SPUI)
U.S. 50 (Arlington Boulevard) at Gallows Road, Falls Church, Va.

A SPUI is also known as:

  • Urban interchange
  • Single-point interchange (SPI)
  • Single-point diamond

What Is A SPUI?

  • A grade-separated interchange design where all freeway ramps begin or end at a single signalized intersection on the arterial
  • Right-turn movements onto and off freeway ramps are made at unsignalized intersections separate from the main intersection
  • Interchange can be designed as an overpass or underpass

When Should It Be Considered?

  • At locations:
    • With limited right of way
    • With heavy left-turn traffic volumes onto and off the interstate or primary road ramps
    • With space to accommodate wider intersection and structure widths

Benefits

  • Improved safety: With only one signalized intersection rather than two at a conventional diamond interchange, vehicles only cross paths at one location.
  • Increased efficiency: Main intersection operates with three traffic signal phases rather than four phases in a conventional diamond interchange, which reduces overall interchange delay.
  • Increased capacity: Design allows left turns to be made at higher speeds, which increases the capacity of the main intersection.
  • Fewer traffic signals: A single signalized intersection, rather than two intersections at a conventional diamond interchange, improves travel times on the arterial.

How to Navigate

The image below shows how to navigate a SPUI. Click the image to view a larger version or watch the video.

SPUI navigation diagram

Conflict Points

The number of conflict points (locations where vehicle travel paths intersect) is one metric that can be used to evaluate the safety of an innovative intersection or interchange.

There are three categories: crossing, merging or diverging.

In general, merging and diverging conflict points — where vehicles are moving in the same direction — are associated with less severe crash types than crossing conflict points where vehicles are moving in opposite directions.

The diagrams below compare the possible vehicle travel movements and associated conflict points at a conventional diamond interchange to a SPUI.

These represent a general case, with one travel lane in each direction, and don't take into account pedestrian or bicycle movements at an intersection or interchange.

When compared to a conventional diamond interchange, a SPUI has two additional crossing conflict points.

Conventional Diamond Interchange: Conflict Points

Conflict Point Diagram

SPUI: Conflict Points

Conflict Point Diagram

Resources

Virginia Department of Transportation

Page last modified: Nov. 7, 2019