Diverging diamond interchange

A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD),[1][2] 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.[2] The crossovers may employ one-side overpasses or be at-grade and controlled by traffic light.

This article reflects countries that drive on the right. For countries that drive on the left, reverse right and left.

A diagram illustrating traffic movements in the interchange
Plan of rejected diverging diamond interchange in Findlay, Ohio

The diverging diamond interchange has advantages in both efficiency and safety, and—despite having been in use in France since the 1970s—was cited by Popular Science as one of the best engineering innovations of 2009[3] and in the U.S. has been promoted as part of the Federal Highway Administration's Every Day Counts initiative.[4] 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.[5][6]

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
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.

The first known diverging diamond interchanges were in France in the communities of Versailles (A13 at D182), Le Perreux-sur-Marne (A4 at N486) and Seclin (A1 at D549), all built in the 1970s.[7] The ramps of the first two have since been reconfigured to accommodate ramps of other interchanges, but they continue to function as diverging diamond interchanges. The interchange in Seclin (at 50°32′41″N 3°3′21″E) between the A1 and Route d'Avelin was somewhat more specialized than in the diagram at right: eastbound traffic on Route d'Avelin intending to enter the A1 northbound must keep left and cross the northernmost bridge before turning left to proceed north onto A1; eastbound traffic continuing east on Route d'Avelin must select a single center lane, merge with A1 traffic that is exiting to proceed east, and cross a center bridge. All westbound traffic that is continuing west or turning south onto A1 uses the southernmost bridge.

In the United States 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.[8] By 2006, ODOT had reconsidered, instead adding lanes to the existing overpass.[9][10]

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

The Missouri Department of Transportation was the first US agency to construct one, in Springfield at the junction between I-44 and Missouri Route 13 (at 37.2503°N 93.3107°W / 37.2503; -93.3107 (Springfield, Missouri diverging diamond interchange)). Construction began the week of January 12, 2009, and the interchange opened on June 21, 2009.[11][12] This interchange was a conversion of an existing standard diamond interchange, and used the existing bridge.[13]

In 2010, the Federal Highway Administration released a publication titled "Alternative Intersections/Interchanges: Informational Report (AIIR)"[14] 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.[15]

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.[16] 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.[17] That same day in Highland, Utah the seventh U.S. diverging diamond interchange opened at the intersection of I-15 and Timpanogos Highway.[18] According to the U.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]

2016 saw the introduction of diverging diamond interchages to three states. In February, the Oregon Department of Transportation opened one in Phoenix.[20][21] In October, the New Mexico Department of Transportation converted the crossing of NM 14 (Cerrillos Road) and Interstate 25 in Santa Fe.[22] 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.[23][24]

The first interchange in Canada opened on August 13, 2017, at Macleod Trail and 162 Avenue South in Calgary, Alberta[25] followed by one in Regina, Saskatchewan the next year as part of the Regina Bypass project.[26]

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.[27][28]

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.[29]

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.[30][31]

Use

Operational

As of October 14, 2022, over 160 DDIs were operational across the world including:

  • 3 in Australia with more planned[32][33][34]
  • 1 in Belgium[35]
  • 3 in Canada[36]
  • 1 in Denmark opened September 17, 2017[37]
  • 2 in France, built in 1970s
  • 2 in Malaysia
  • 2 in Saudi Arabia
  • 2 in South Africa
  • 1 in the United Arab Emirates
  • 1 in Costa Rica
  • Over 150 in the United States of America with 80 more under construction[38]

Advantages
  • Two-phase signals with short cycle lengths, significantly reducing delay.[39]
  • 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.[2]
  • Increases the capacity of an existing overpass or underpass, by removing the need for turn lanes.
  • Costs significantly less than a normal interchange.[40]

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.[41]
  • 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).[42][41] 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 at both intersections for both directions simultaneously.
  • Highway bus stops must be sited outside the interchange.
  • 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 a median U-turn crossover. This affects several use cases:[41]
    • Drivers who take the wrong exit
    • Bypassing a crash at the bridge
    • Allowing an oversize load to bypass a low bridge

Further considerations
  • No standards currently exist for this design.
  • The design depends on site-specific conditions.
  • 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.

Double crossover merging interchange
3D computer generated DCMI
DCMI traffic flow patterns

A free-flowing interchange variant, patented in 2015,[43] has received recent attention.[44][45][46] 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. As of 2016, no such interchanges have been constructed.

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).[47]

See also

References
  1. Hughes, Warren; Jagannathan, Ram (October 2009). "Double Crossover Diamond Interchange". Federal Highway Administration. FHWA-HRT-09-054. Retrieved April 22, 2012.
  2. "Missouri's Experience with a Diverging Diamond Interchange" (PDF). Missouri Department of Transportation. May 2010. p. 4. Archived from the original (PDF) on May 30, 2010.
  3. "Gallery: Looking Back at the 100 Best Innovations of 2009". Popular Science. Retrieved January 20, 2012.
  4. Schroeder, Bastian; Cunningham, Chris; Ray, Brian; Daleiden, Andy; Jenior, Pete; Knudsen, Julia (August 2014). Diverging Diamond Interchange Informational Guide (PDF). Washington, DC: Federal Highway Administration Office of Safety.
  5. "Diverging Diamond Interchange". OHM Advisors. Archived from the original on February 19, 2009. Retrieved November 6, 2008.
  6. Gilbert Chlewicki: About History
  7. Staff (June 13, 2013). "I-64 Interchange at Route 15, Zion Crossroads". Virginia Department of Transportation. Archived from the original on November 27, 2013. Retrieved December 11, 2013.
  8. Patch, David (May 2, 2005). "French Connection May Control Traffic Flow". The Blade. Toledo, Ohio. Retrieved April 8, 2014.
  9. Sedensky, Matt (March 30, 2006). "Missouri Drivers May Go to the Left". Star-News. Wilmington, North Carolina. Associated Press. Retrieved April 8, 2014.
  10. "Wrong Way? Not in Kansas City". Land Line Magazine. March 31, 2006. Retrieved April 8, 2014.
  11. Staff (April 2009). "I-44/Route 13 Interchange Reconstruction: Diverging Diamond Design". Missouri Department of Transportation. Archived from the original on June 7, 2011. Retrieved May 19, 2009.
  12. Springfield District Office (June 19, 2008). "Public Meeting Tuesday, June 24, On I-44/Route 13 Reconstruction To Reduce Congestion, Improve Safety" (Press release). Missouri Department of Transportation. Retrieved June 19, 2008.
  13. "Archived copy" (PDF). www.ijtte.com. Archived from the original (PDF) on December 9, 2019. Retrieved January 11, 2022.{{cite web}}: CS1 maint: archived copy as title (link)
  14. Hughes, Warren; Jagannathan, Ram; Sengupta, Dibu & Hummer, Joe (April 2010). Alternative Intersections/Interchanges: Informational Report (AIIR) (Report). Federal Highway Administration.
  15. Edara, Praveen K.; Bared, Joe G. & Jagannathan, Ramanujan. "Diverging Diamond Interchange and Double Crossover Intersection: Vehicle and Pedestrian Performance" (PDF).
  16. "DDI Openings by Date". Diverging Diamond Interchange. Retrieved February 19, 2023.
  17. "US 68 (Harrodsburg Road) Widening". Stantec. Retrieved February 19, 2023.
  18. "DDI Openings by Date". Diverging Diamond Interchange. Retrieved February 19, 2023.
  19. Office of Safety (June 1, 2014). "Diverging Diamond Interchange: Interstate 15 and Timpanogos Highway, Lehi, UT". United States Federal Highway Administration.
  20. Project Profile: I-5 Fern Valley Interchange. Federal Highway Administration https://www.fhwa.dot.gov/ipd/project_profiles/or_i5_fern_valley_interchange.aspx. Retrieved March 1, 2023. {{cite web}}: Missing or empty |title= (help)
  21. Diverging Diamond Interchange. Advanced Transportation Solutions (ATS) America https://divergingdiamond.com/ddi-openings-by-date/. Retrieved March 1, 2023. {{cite web}}: Missing or empty |title= (help)
  22. "Unique I-25 interchange now open for Santa Fe drivers". KRQE NEWS 13 - Breaking News, Albuquerque News, New Mexico News, Weather, and Videos. October 31, 2016. Retrieved June 14, 2022.
  23. "Delaware Department of Transportation - SR 72/SR 1 Diverging Diamond Interchange". deldot.gov. Retrieved June 29, 2020.
  24. "DelDOT Interactive Maps". Delaware Department of Transportation. Retrieved June 29, 2020.
  25. Yourex-West, Heather (August 14, 2017). "Canada's first 'diverging diamond interchange' now open to Calgary traffic - Calgary | Globalnews.ca". globalnews.ca. Retrieved March 7, 2019.
  26. "Saskatchewan's First DDI".
  27. "Bruce Highway Upgrade Caloundra Road to Sunshine Motorway". sc-tmrwcmgr-cd.azurewebsites.net. Retrieved August 29, 2021.
  28. Jones, Lauren (December 1, 2019). "Major contractor opens Australian first Diverging Diamond Interchange". Roads & Infrastructure Magazine. Retrieved August 29, 2021.
  29. "This New, Trippy Interchange Will Have You Driving On The Wrong Side Of The Road In Virginia". DCist. Retrieved December 6, 2019.
  30. "SR 120 @ Union Road". Diverging Diamond Interchange. Retrieved May 31, 2021.
  31. "California's first diverging diamond interchange just debuted in Manteca". abc10.com. November 20, 2020. Retrieved May 31, 2021.
  32. "Sydney's worst roundabout gets $100m upgrade, work won't start for three years". April 26, 2022.
  33. "Burleigh Diverging Diamond Interchange". BG&E. Retrieved September 28, 2022.
  34. "Gympie Arterial Road and Strathpine Road (Bald Hills), improve intersection". sc-tmrwcmgr-cd.azurewebsites.net. Retrieved November 22, 2022.
  35. Coopman, Bart; Baert, Kate (October 14, 2022). "Goed nieuws voor de mobiliteit rond Waregem: "De Vlecht" aan het afrittencomplex is geopend". Focus-WTV (in Dutch). Archived from the original on October 14, 2022. Retrieved October 14, 2022.
  36. "Ontario's first diverging diamond interchange opens. Here's how it works". September 25, 2022.
  37. "Ministeren markerede ibrugtagning af det dynamiske ruderanlæg". Vejdirektoratet.
  38. "Diverging diamond interchange". Washington State Department of Transportation. Retrieved September 27, 2022.
  39. "Missouri's Experience with a Diverging Diamond Interchange" (PDF). www.modot.org. May 2010. p. 5. Archived from the original (PDF) on May 30, 2010.
  40. "Diverging Diamond Interchange". Retrieved June 7, 2020.
  41. "Missouri's Experience with a Diverging Diamond Interchange" (PDF). www.modot.org. May 2010. p. 6. Archived from the original (PDF) on May 30, 2010.
  42. "The 'Diverging Diamond' Interchange Is an Abomination - Sarah Goodyear". The Atlantic Cities. September 20, 2011. Archived from the original on November 13, 2011. Retrieved April 22, 2014.
  43. "United States Patent 8,950,970: Double Crossover Merging Interchange". United States Patent and Trademark Office. February 10, 2015. Retrieved October 4, 2016.
  44. "TRAFFIC ENGINEERING COUNCIL BEST PAPER and BEST PRODUCT AWARD: Past Recipients". Institute of Transportation Engineers. 2016. Archived from the original on October 4, 2016. Retrieved 4 October 2016.
  45. "Alternative Intersections & Interchanges Symposium" (PDF). Transportation Research Board. July 21, 2014. Archived from the original (PDF) on March 5, 2016. Retrieved 4 October 2016.
  46. Buteliauskas, Stanislovas; Juozapavičius, Aušrius (June 15, 2014). "Interchange of a New Generation Pinavia" (PDF). Military Academy of Lithuania. Archived from the original (PDF) on October 4, 2016. Retrieved 4 October 2016.
  47. "Interstate 10 and State Route 210 Study | Department of Transportation". azdot.gov. Retrieved September 7, 2023.

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