Diverging diamond interchange

thumb|A diverging diamond at [[Interstate 285 (Georgia)|Interstate 285 and Camp Creek Parkway in East Point, Georgia ]]

thumb|right|A diagram illustrating traffic movements in the interchange

thumb|right|Plan of rejected diverging diamond interchange in [[Findlay, Ohio]]

A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a subset of diamond interchange in which the opposing directions of travel on the non-freeway road cross each other on either side of the interchange so that traffic crossing the freeway on the overpass or underpass is operating on the opposite driving side from that which is customary for the jurisdiction. despite having been sparsely used in its contemporary form in France as early as the 1970s. It has been promoted in the U.S. as part of the Federal Highway Administration's Every Day Counts initiative. The flow through a diverging diamond interchange using overpasses at the crossovers is limited only by weaving, and the flow through an implementation using traffic lights is subject to only two clearance intervals (the time during which all lights are red so that the intersection may fully clear) per cycle.

The greatest safety concern of the interchange stems from its relative rarity, as drivers instinctively trying to stay on the customary side of the road could use the crossover intersections to turn against the posted direction of travel. This is a rare occurrence; it is possible only when traffic is so sparse that no cars from the oncoming direction are stopped at the light, and clear signage further reduces the likelihood of such errors.

History

upright=1.6|thumb|Pictures from the first diverging diamond interchange in the United States, in [[Springfield, Missouri Top left: Traffic enters the interchange along Missouri Route 13 Top right: Traffic crosses over to the left side of the road Bottom left: Traffic crosses over Interstate 44 Bottom right:Traffic crosses back over to the right side of the road.]]

thumb|Lunchtime traffic at the diverging diamond interchange at the [[James River Freeway and Route 13 in Springfield]]

The first known diverging diamond interchanges were built in France during the 1970s, in the communities of Versailles (A13 at D182), Nogent-sur-Marne (A4 at N486) and Seclin (A1 at D549; featuring an asymmetrical 2/4 lane layout). In 2005, the Ohio Department of Transportation (ODOT) considered reconfiguring the existing interchange on Interstate 75 at U.S. Route 224 and State Route 15 west of Findlay as a diverging diamond interchange to improve traffic flow. Had it been constructed, it would have been the first DDI in the United States. By 2006, ODOT had reconsidered, instead adding lanes to the existing overpass.

thumb|Southbound approach to the I-44/Route 13 interchange in Springfield

The Missouri Department of Transportation (MoDOT) was the first US agency to construct one, in Springfield at the junction between I-44 and Missouri Route 13 (at ). Construction began the week of January 12, 2009, and the interchange opened on June 21, 2009. This interchange was a conversion of an existing standard diamond interchange, and used the existing bridge. MoDOT reports that traffic congestion for left turns at the intersection cleared up immediately, and crashes dropped by 40–50%. with a chapter dedicated to this design. Additional research was conducted by a partnership of the Virginia Polytechnic Institute and State University and the Turner-Fairbank Highway Research Center and published by Ohio Section of the Institute of Transportation Engineers.

On August 14, 2011, the Kentucky Transportation Cabinet (KYTC) completed conversion of the intersection of U.S. Route 68 and Kentucky Route 4 in Lexington to a diverging diamond design, the first in the state and the sixth completed nationally. Stantec, the engineers who completed the upgrades to the interchange, noted the solution while providing substantial cost savings over other possible options also has decreased accidents by 45 percent, improved traffic flow to more than 35,000 vehicles per day, and incorporated KYTC's goal to provide new paths for bicycles and pedestrians through the area. That same day in Highland, Utah the seventh U.S. diverging diamond interchange opened at the intersection of I-15 and Timpanogos Highway.

The year 2016 saw the introduction of diverging diamond interchanges by three states. In February, the Oregon Department of Transportation opened one in Phoenix. In October, the New Mexico Department of Transportation converted the crossing of NM 14 (Cerrillos Road) and Interstate 25 in Santa Fe. In November, the Delaware Department of Transportation completed the conversion of the DE-1 and DE-72 (Wrangle Hill Rd) overpass west of Delaware City.

The first interchange in Canada opened on August 13, 2017, at Macleod Trail and 162 Avenue South in Calgary, Alberta followed by one east of Regina, Saskatchewan the next year as part of the Regina Bypass project.

In the 2010s MoDOT designed a hybrid of a diverging diamond interchange and a roundabout that they call a "". The first opened at Interstate 49/U.S. Route 71 and 155th Street where Belton meets Grandview and Kansas City on December 15, 2017, with a second following on May 11, 2018, in nearby Lee's Summit at U.S. Route 50 and Missouri Route 291/Jefferson Street.

The first diverging diamond interchange in Australia opened to traffic by the Queensland Department of Transport and Main Roads on November 28, 2019. The interchange, located in Caloundra, Queensland, connects Caloundra Road to the Bruce Highway. The former interchange was upgraded and converted as part of the larger Bruce Highway Upgrade Program.

In December 2019, the Virginia Department of Transportation completed the conversion of the interchange at Courthouse Road and I-95 in Stafford, VA into a diverging diamond interchange.

In 2020, the California Department of Transportation (Caltrans) completed the first diverging diamond interchange in California. An interchange at State Route 120 and Union Road in Manteca, California was converted to this interchange and opened to traffic on November 25.

Use

Operational

thumb|Diverging diamond interchange on [[Queen Elizabeth Way in Niagara-on-the-Lake, Ontario, Canada]]

, over 170 DDIs were operational across the world including:

Two in Australia, with more planned
1 in Belgium
3 in Canada
1 in Denmark, opened September 17, 2017
2 in France, built in 1970s
8 in Malaysia
2 in Saudi Arabia
2 in South Africa
1 in the United Arab Emirates
1 in Costa Rica
>150 in the United States, with ~80 more under construction
1 in Turkey

Advantages

Compared to a diamond interchange, the advantages of a diverging diamond interchange are:

Two-phase signals with short cycle lengths, significantly reducing delay.
Reduced horizontal curvature reduces the risk of off-road crashes.
Increases the capacity of turning movements to and from the ramps.
Potentially reduces the number of lanes on the crossroad, minimizing space consumption.
Reduces the number of conflict points, thus theoretically improving safety.

Disadvantages

Drivers may not be familiar with configuration, particularly with regard to merging maneuvers along the opposite side of the roadway or the crossover flow of traffic.
Pedestrian (and other sidewalk-user) access requires at least four crosswalks (two to cross the two signalized lane crossover intersections, while two more cross the local road at each end of the interchange). has received recent attention. Called the double crossover merging interchange (DCMI), it includes elements from the diverging diamond interchange, the tight diamond interchange, and the stack interchange. It eliminates the disadvantages of weaving and of merging into the outside lane from which the standard DDI variation suffers. A highway U-turn requires weaving, however.

A partial DCMI has existed at the I-45/SH 6/SH 146 interchange in Bayou Vista, Texas, since at least 1969. As of 2025, however, construction is underway to replace the DCMI as part of a widening project on I-45.

Three-level diverging diamond interchange

Another variation of the diverging diamond was developed by the Arizona Department of Transportation (ADOT) as part of their I-10 widening/SR 210 extension project near Tucson, Arizona. The interchange (I-10 exit 270 at Kolb Road) will be reconfigured as a combination of both a diverging diamond and a three-level diamond interchange. The ramps (the top level/Kolb Road) would carry thru traffic while the diverging diamond (the second level/interchange) would be for traffic getting on or off the freeway (the third level/I-10).

References

External links

DDI Guideline – A UDOT Guide to Diverging Diamond Interchanges , Utah Department of Transportation, June 2014
Transportation engineers discuss the design of the fifth U.S. DDI in Alcoa, TN
Video of Paramics Traffic Simulation software modeling a Double Crossover Diamond Interchange
Diverging Diamond Interchange Visualization, Instructional video on how to drive in a DDI, NCDOTcommunications, published on March 10, 2011
Images of Diverging Diamond Interchange in Springfield, Missouri the first in North America.
Animation of Diverging Diamond Interchange under construction at Elmhurst Road on Interstate 90 near Elk Grove, Illinois, to be completed in 2016
Animation of Diverging Diamond Interchange at I-590/Winton Road (Rochester, New York)

Examples

—Diverging diamond in Versailles, France
Diverging diamond in Seclin, France
—Diverging diamond in Springfield, Missouri

de:Anschlussstelle (Autobahn)#DDI / DCD