Single-Point Urban Interchange (SPUI)

Innovative Intersections

Overhead photograph of a SPUI. The photograph shows the cross street left-turning traffic moving through the intersection simultaneously in both directions, which the through traffic is stopped at the traffic light.

Example SPUI in McKinney, TX

What is a SPUI?

Icon representing a Single-Point Urban Interchange (SPUI) with intersecting traffic flow arrows.

A Single-Point Urban Interchange (SPUI) is a type of innovative intersection designed to move large volumes of traffic safely and efficiently.

Unlike traditional interchanges, a SPUI uses a single traffic signal to control all movements through the intersection. This design allows opposing left-turn movements to happen simultaneously without directly crossing paths of travel. This helps traffic flow more smoothly and reduces delays.

Because left-turn traffic often creates congestion at busy intersections, SPUIs are especially helpful where heavy left-turn volumes occur. They can also work well along corridors with closely spaced intersections.

Illustration of a Single Point Urban Interchange (SPUI) showing how opposing left-turn movements pass through a single central signal, through traffic proceeds straight, right-turning vehicles yield, and pedestrians cross using marked crosswalks.

Design principles

A SPUI has several features that help move traffic safely and efficiently.

Solid blue icon of a vertical traffic signal with three circular lenses, symbolizing signalized control at a roadway crossover where traffic movements are directed by phased signal operations.

Single traffic signal

All traffic movements pass through one centrally located signal. This simplifies signal timing and helps keep traffic moving.

Blue icon of a roadway crossing where one road travels over another on a bridge, representing a grade-separated intersection, overpass, or underpass configuration that separates traffic movements onto different elevations.

Overpass or underpass

The main roadway passes over or under the cross street, eliminating at-grade conflict points and improving flow.

Left-turn lanes

Dedicated left-turn lanes allow drivers traveling in opposite directions to make left turns at the same time without crossing each other's paths. This reduces delays and improves safety.

Ramps

Entrance and exit ramps connect directly to the intersection and provide efficient access to and from the highway.

Icon representing efficient signal timing, where a single traffic signal manages all traffic movements to improve flow, reduce congestion, and minimize vehicle delays and wait times.

Signal phasing

Because a single signal controls all movements, traffic can be managed more efficiently. This reduces congestion and minimizes delays and wait times.

Why the design works

By reducing conflict points and allowing key traffic movements, especially left turns, to happen
simultaneously, a SPUI can handle high traffic volumes while improving safety and reducing delays.

Design characteristics

Common to all SPUIs

Simultaneous left turns.

Clear separation between main roadway and cross street.

Enables opposing left-turns to proceed simultaneously without crossing paths.
Continuous right-turn lanes.

Site dependent

Can be designed as an overpass or underpass, depending on constraints.

Based on the roadway, available right-of-way, and other site constraints.

Depends on current and projected traffic volumes.

Depends on traffic volumes, operational needs, and expected turning movements.

Customized based on traffic patterns, pedestrian and cyclist activity, and nearby intersections.

Emphasis on pedestrian safety in places with heavy foot-traffic or near schools, etc.
Determined by specific location, users, connections to nearby destinations, and community needs.

Dependent on specific location, users, and community needs.

Limitations of SPUIs

Locations where frontage road through movements are a priority, as additional treatment may be required.
Where the SPUI is the overpass, it may require a larger bridge structure than a traditional interchange.

Benefits of SPUIs

Enhanced safety

SPUIs reduce the number of conflict points where vehicles cross paths. This designcan help reduce the chance of crashes and improve traffic operations.

Fewer conflict points
Wider turns for large vehicles
Safet left-turn movements

Diagram of traffic flow at a four-way intersection. It highlights each location a conflict is possible, including diverging traffic, merging traffic, and crossing traffic.

Diagram of a SPUI showing lane markings and turning paths for vehicles. It features each location a conflict is possible, including diverging traffic, merging traffic, and crossing traffic.

Better traffic flow

A SPUI means better traffic flow as it allows more vehicles tomove through an intersection, reducing delays and travel times. This means:

Reduced delays
Shorter travel and wait times
More efficient traffic signal operation
Improved traffic flow during peak travel periods
Simpler coordination with nearby intersections

Efficient use of space and resiliency

This type of innovative intersection can provide more traffic capacity and often
requires less right-of-way than traditional interchanges. This can make them a
practical solution in some areas, including:·