Adiverging diamond interchange (DDI), also called adouble crossover diamond interchange (DCD),[1][2] is a subset ofdiamond 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 oppositedriving side from that which is customary for the jurisdiction.[2] The crossovers may employ one-side overpasses or be at-grade and controlled bytraffic lights.
The diverging diamond interchange has advantages in both efficiency and safety, and was cited byPopular Science as one of the best engineering innovations of 2009,[3] despite having been sparsely used in its contemporary form in France as early as the 1970s.[4] It has been promoted in the U.S. as part of the Federal Highway Administration'sEvery Day Counts initiative.[5] The flow through a diverging diamond interchange using overpasses at the crossovers is limited only byweaving, 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.[6][7]
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.[citation needed]
Pictures from the first diverging diamond interchange in the United States, inSpringfield, Missouri Top left: Traffic enters the interchange alongMissouri Route 13 Top right: Traffic crosses over to the left side of the road Bottom left: Traffic crosses overInterstate 44 Bottom right:Traffic crosses back over to the right side of the road.Lunchtime traffic at the diverging diamond interchange at theJames River Freeway and Route 13 in Springfield
The first known diverging diamond interchanges were built in France during the 1970s, in the communities ofVersailles (A13 at D182),Nogent-sur-Marne (A4 at N486) andSeclin (A1 at D549; featuring an asymmetrical 2/4 lane layout).[4] The Nogent-sur-Marne interchange originally was acontraflow left interchange, then reorganized as a diverging diamond interchange in the 1980-90s, and has been completely rebuilt with a more standard layout in 2019; the other two continue to function as diverging diamond interchanges. A three-way derivative which may be considered a related precursor was also built in the UK on theM1 in 1969 to provide access toLondon Gateway services (formerly Scratchwood Services).
In the United States, invention of the diverging diamond interchange is credited to Gilbert Chlewicki.[8] In 2005, theOhio Department of Transportation (ODOT) considered reconfiguring the existing interchange onInterstate 75 atU.S. Route 224 andState Route 15 west ofFindlay as a diverging diamond interchange to improve traffic flow. Had it been constructed, it would have been the first DDI in the United States.[9] By 2006, ODOT had reconsidered, instead adding lanes to the existing overpass.[10][11]
Southbound approach to the I-44/Route 13 interchange in Springfield
On August 14, 2011, theKentucky Transportation Cabinet (KYTC) completed conversion of the intersection ofU.S. Route 68 andKentucky Route 4 inLexington to a diverging diamond design, the first in the state and the sixth completed nationally.[17]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.[18] That same day in Highland, Utah the seventh U.S. diverging diamond interchange opened at the intersection ofI-15 and Timpanogos Highway.[17] According to theU.S. Department of Transportation the goals of this intersection upgrade were similar, increasing traffic capacity and improved pedestrian and bicycle access while reaching these goals without requiring substantial revisions to the existing interstate overpass. Quoting a June 2014 USDOT publication, "the DDI has made travel more efficient and accessible for all users."[19]
In December 2019, theVirginia Department of Transportation completed the conversion of the interchange at Courthouse Road and I-95 in Stafford, VA into a diverging diamond interchange.[34]
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.[47]
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).[48][47] This could be mitigated by signalizing all movements without impacting the two-phase nature of the interchange’s signals.
Free-flowing traffic in both directions on the non-freeway road is impossible as the signals cannot be green for both directions simultaneously.
Highway bus stops must be sited outside the interchange.[citation needed]
Allowing exiting traffic to re-enter the through road in the same direction requires leaving the interchange on the local road and turning around, e.g., via amedian U-turn crossover. This affects several use cases:[47]
Some factors make turning left onto a diverging diamond interchange from the highway ramp more hazardous: 1) There is a yield sign instead of a traffic light. 2) The driver can not see if the light for the through traffic is red or green. 3) The visible distance to see the oncoming through traffic from that vantage is very short. All of these combined results in the driver entering a potentially very busy interchange without sufficient information.[citation needed]
Additional signage, lighting, and pavement markings are needed beyond the levels for a standard diamond interchange.
Local road should be a low-speed facility, preferably under 45 mph (72 km/h) posted speed on the crossroad approach. However, this may be mitigated by utilizing a higher design speed for the crossing movements.
3D computer generated DCMIDCMI traffic flow patterns
Afree-flowing interchange variant, patented in 2015,[49] has received recent attention.[50][51][52] Called thedouble crossover merging interchange (DCMI), it includes elements from the diverging diamond interchange, thetight diamond interchange, and thestack 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 theI-45/SH 6/SH 146 interchange inBayou Vista, Texas, since at least 1969.[53] As of 2025, however, construction is underway to replace the DCMI as part of a widening project on I-45.[54]
Another variation of the diverging diamond was developed by the Arizona Department of Transportation (ADOT) as part of theirI-10 widening/SR 210 extension project nearTucson, Arizona. The interchange (I-10 exit 270 at Kolb Road) will be reconfigured as a combination of both a diverging diamond and athree-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).[55]
^Buteliauskas, Stanislovas; Juozapavičius, Aušrius (June 15, 2014)."Interchange of a New Generation Pinavia"(PDF). Military Academy of Lithuania. Archived fromthe original(PDF) on October 4, 2016. RetrievedOctober 4, 2016.
^United States Army Corps of Engineers; United States Geological Survey (1969).Virginia Point Quadrangle (Topographic map). 1:24,000. 7.5 Minute Series. Washington, DC: United States Geological Survey. RetrievedSeptember 6, 2025 – via University of North Texas Libraries.
^Houston District (February 6, 2018).I-45 at Texas City Wye (Map). Scale not given. Texas Department of Transportation. Sheet 5. RetrievedSeptember 6, 2025 – via City of La Marque, Texas.
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