Diverging Diamond Interchange (DDI)
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Diverging Diamond Interchange (DDI)

Innovative Intersections

What is a DDI?

A Diverging Diamond Interchange (DDI) is a grade-separated, signalized interchange design that shifts cross street traffic to the opposite side of the roadway through a series of crossovers. This design eliminates left‑turn conflicts with opposing traffic, reduces the number of vehicle conflict points, and improves overall interchange safety and operational efficiency.

Diverging Diamond Interchange (DDI) concept diagram. The graphic includes the following informational callouts: 1. Depending on their level of comfort, cyclists may navigate the intersection using vehicle or pedestrian paths. 2. Pedestrians use marked crosswalks to safely navigate the interchange. 3. To continue straight on the arterial, follow lane markings and traffic signals to cross to the left side of the arterial, and then cross to the right side after passing through the interchange. 4. To turn left onto a freeway ramp from the arterial, follow lane markings and traffic signals to cross to the left side of the arterial, and then turn left onto the ramp. 5. To turn right onto a freeway ramp from the arterial, use the right-turn lane like at a conventional diamond interchange. 6. To turn left from a freeway ramp, follow lane markings and traffic signals to stay on the left side of the arterial, and then cross to the right side after passing through the interchange. 7. To turn right from a freeway ramp, use the right-turn lane like at a conventional diamond interchange. Note: For simplicity, only two directions of traffic are shown. Opposing traffic follows similar routes.

TXDOT RDM Figure 14-38: Diverging Diamond Interchange Concept (DDI)

Source: Virginia DOT, used by permission

Design principles

DDIs are characterized by the following design principles:

Crossovers

Traffic on the cross street briefly crosses to the opposite side of the roadway 

Signalized

Two-phase traffic signals control each crossover

Reduced Speeds

Geometric curvature encourages slower, consistent vehicle speeds through the interchange

Design characteristics

Common to all DDIs

Left-turns from the cross street do not conflict with opposing traffic between the limits of the crossovers

DDIs are grade separated from an access-controlled roadway 

Through movements on frontage roads are not accommodated without additional grade-separated bypasses

Site dependent

May be provided for frontage road traffic to avoid signalized intersections

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

Pedestrian and bicycle facilities can be incorporated based on local context and needs

When to consider a DDI

  • High left‑turn volumes where conventional signal phasing contributes to delay or safety concerns
  • Conventional diamond interchanges operating at or near capacity
  • Locations with a documented crash history
  • Sites where the existing bridge can be reused to limit cost and construction impacts

DDI limitations

  • Locations where frontage road through movements are a priority, as additional treatment may be required
  • More constrained sites where fitting crossover geometry may influence layout or adjacent development
  • At cross streets where pre-existing adjacent driveway access may be restricted or prohibited
  • Driver confusion may occur as drivers are placed on the “wrong” side of the road between the crossovers
Aerial view of a diverging diamond interchange with traffic briefly crossing to the left between ramps and a divided highway.

Benefits of DDIs

  • Reduces the number of potential vehicle conflict points by shifting traffic and simplifying signal phasing
  • Eliminates left-turn crashes and significantly reduces right-angle and rear-end crashes compared to conventional diamond interchanges
  • Studies have shown up to a 46% reduction in total crashes (Source: Missouri DOT)
  • Through and left-turning vehicles can move simultaneously, reducing congestion
  • Accommodates higher left-turn volumes without adding lanes
  • Pedestrians and bicyclists cross fewer lanes, fewer conflict points, and have more crossing time per signal phase
  • Central pathways provide refuge and protection, improving overall comfort and safety 

Educational materials

Videos

Fact sheets

Additional resources

Have questions about DDIs? Please reach out!
innovative.intersections@txdot.gov