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Interchange Types

A completed SPUI interchange at US-131 and 44th Street in city of Wyoming, Kent County.
Department of Transportation

Interchange Types

Single-Point Urban Interchange (SPUI)

A Single-Point Urban Interchange (SPUI) is a type of highway interchange. In a SPUI (pronounced "Spooey"), a single traffic signal at the center of the interchange controls all left turns. Drivers make opposing left-turns at the same time under the protection of this signal.


  • Constructed where there is not enough room for a standard interchange.
  • Ideal for urban areas.
  • Allows more vehicles to make a turn and clear the interchange in one traffic signal cycle.
  • Allows long, gradual turns so larger vehicles have more room to navigate the interchange.
  • It can be coordinated with cross-street signal systems.

Diverging Diamond Interchange (DDI)

What is a diverging diamond interchange?

A diverging diamond interchange (DDI) is an alternative interchange that improves safety, increases traffic flow, and reduces construction cost.

DDIs have been successfully implemented at several locations throughout Michigan in recent years, providing a number of benefits:

  • Reduced opportunities for collisions
  • Greater capacity and efficiency
  • Reduced backup congestion
  • Easier navigation
  • Meets needs of all road users
A diverging diamond interchange in the Metro Detroit area.

How to drive a DDI?

  • Follow Signs: Following the signs, signals and pavement markings, motorists cross over to the left side after the first set of traffic signals.
  • Free Flow Left Turns: All left turns onto the freeway are free flow, meaning vehicles do not have to stop to access the ramp.
  • Through-Traffic: Vehicles going straight simply proceed through a second set of traffic signals and cross back to the right side of the road.