Diverging diamond interchange
A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a type of diamond interchange in which the two directions of traffic on the non-freeway road cross to the opposite side on both sides of the bridge at the freeway. It is unusual in that it requires traffic on the freeway overpass (or underpass) to briefly drive on the opposite side of the road from what is customary for the jurisdiction. The crossover "X" sections can either be traffic-light intersections or one-side overpasses to travel above the opposite lanes without stopping, to allow nonstop traffic flow when relatively sparse traffic.
Like the continuous flow intersection, the diverging diamond interchange allows for two-phase operation at all signalized intersections within the interchange. This is a significant improvement in safety, since no long turns (e.g. left turns where traffic drives on the right side of the road) must clear opposing traffic and all movements are discrete, with most controlled by traffic signals. Its at-grade variant can be seen as a two-leg continuous flow intersection.
Additionally, the design can improve the efficiency of an interchange, as the lost time for various phases in the cycle can be redistributed as green time—there are only two clearance intervals (the time for traffic signals to change from green to yellow to red) instead of the six or more found in other interchange designs.
A diverging diamond can be constructed for limited cost, at an existing straight-line bridge, by building crisscross intersections outside the bridge ramps to switch traffic lanes before entering the bridge. The switchover lanes, each with 2 side ramps, introduce a new risk of drivers turning onto an empty, wrong, do-not-enter, exit-lane and driving the wrong way down a freeway exit ramp to confront high-speed, oncoming traffic. Studies have analyzed various roadsigns to reduce similar driver errors.
Diverging diamond roads have been used in France since the 1970s. However, the diverging diamond interchange was listed by Popular Science magazine as one of the best innovations in 2009 (engineering category) in "Best of What's New 2009".
Prior to 2009 the only 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. (The ramps of the first two have been reconfigured to accommodate ramps of other interchanges, but they continue to function as diverging diamond interchanges.)
Despite the fact that such interchanges already existed, the idea for the DDI was "reinvented" around 2000, inspired by the former "synchronized split-phasing" type freeway-to-freeway interchange between Interstate 95 and I-695 north of Baltimore.
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.
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 ). 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.
The interchange in Seclin (at 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.) between the
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. The Federal Highway Administration released a publication titled "Alternative Intersections/Interchanges: Informational Report (AIIR)"  with a chapter dedicated to this design.
As of August 28, 2018, 116 DDIs were operational across the world including:
- 2 in Canada
- 1 in Denmark opened September 17, 2017
- 3 in France, built in 1970s
- 1 in Malaysia
- 2 in Saudi Arabia
- 2 in South Africa
- 1 in the United Arab Emirates
- 104 in the United States of America with 21 more under construction
- Australia – Caloundra Road interchange on the Bruce Highway (Exit 188) in the Sunshine Coast Region of Queensland as part of a wider upgrade. Construction began in May 2017 and is expected to be complete late 2020.
- Belgium – The junction of N4 and N25 in Mont-Saint-Guibert near E411, currently a roundabout, will be converted to a diverging diamond interchange.
- Canada – Glendale Avenue interchange on the Queen Elizabeth Way in Niagara-on-the-Lake, Ontario is planned to be reconstructed as a diverging diamond interchange.
- Lithuania – The existing interchange between A1 and A6 near Kaunas is planned to be reconstructed as a diverging diamond interchange.
- United States – Interstate 5/State Route 510 interchange in Washington state will be reconstructed into a diverging diamond interchange, the first in the state. Construction is planned to start in the middle of 2018 and to be complete in the middle of 2020. FM 60 (Raymond Stotzer Parkway) and FM 2818 (Harvey Mitchell Parkway) at Texas A&M University in College Station, Texas. Construction is expected to last 25 months and began on March 6, 2017, with an estimated cost of $14.1 million.
- 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.
- Increases the capacity of an existing overpass or underpass, by removing the need for turn lanes.
- Costs significantly less than a normal interchange.
- 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). 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 are appropriately 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:
- Drivers who take the wrong exit
- Bypassing a crash at the bridge
- Allowing an oversize load to bypass a low bridge
- 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
A free-flowing interchange variant, patented in 2015, 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. As of 2016, no such interchanges have been constructed.
- Hughes, Warren; Jagannathan, Ram (October 2009). "Double Crossover Diamond Interchange". Federal Highway Administration. FHWA-HRT-09-054. Retrieved April 22, 2012.
- "Missouri's Experience with a Diverging Diamond Interchange" (PDF). www.modot.org. May 2010. p. 4.
- "Diverging Diamond Interchange". OHM Advisors.
- Gilbert Chlewicki: About History
- "Gallery: Looking Back at the 100 Best Innovations of 2009". Popular Science. Retrieved January 20, 2012.
- Staff (June 13, 2013). "I-64 Interchange at Route 15, Zion Crossroads". Virginia Department of Transportation. Retrieved December 11, 2013.
- Chlewicki, Gilbert (2003). "New Interchange and Intersection Designs: The Synchronized Split-Phasing Intersection and the Diverging Diamond Interchange" (PDF). Archived from the original (PDF) on 2011-10-20. Retrieved 2009-10-20.
- Patch, David (May 2, 2005). "French Connection May Control Traffic Flow". The Blade. Toledo, Ohio. Retrieved April 8, 2014.
- Sedensky, Matt (March 30, 2006). "Missouri Drivers May Go to the Left". Star-News. Wilmington, North Carolina. Associated Press. Retrieved April 8, 2014.
- "Wrong Way? Not in Kansas City". Land Line Magazine. March 31, 2006. Retrieved April 8, 2014.
- 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.
- 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.
- Edara, Praveen K.; Bared, Joe G. & Jagannathan, Ramanujan. "Diverging Diamond Interchange and Double Crossover Intersection: Vehicle and Pedestrian Performance" (PDF).
- Hughes, Warren; Jagannathan, Ram; Sengupta, Dibu & Hummer, Joe (April 2010). Alternative Intersections/Interchanges: Informational Report (AIIR) (Report). Federal Highway Administration.
- Ministeren markerede ibrugtagning af det dynamiske ruderanlæg
- "Alternative Intersections and Interchanges". Retrieved 2017-02-03.
- "Bruce Highway Upgrade – Caloundra Road to Sunshine Motorway". Queensland Department of Transport and Main Roads. 18 May 2017. Retrieved 18 May 2017.
- "Un nouvel échangeur pour supprimer les bouchons au carrefour de la N4 et de la N25". RTBF Info (in French). 2018-06-06. Retrieved 2018-06-17.
- "Žemės paėmimo visuomenės poreikiams projektas" (PDF).
- Washington State Department of Transportation. "I-5 - SR 510 Interchange - Reconstruct Interchange". Washington State Department of Transportation. Retrieved 29 April 2018.
- Washington State Department of Transportation (15 September 2016). Diverging Diamond Interchange comes to Washington State. Washington State Department of Transportation. Retrieved 29 April 2018 – via YouTube.
- "FM 60 (Raymond Stotzer Parkway) Overpass Improvement".
- "Missouri's Experience with a Diverging Diamond Interchange" (PDF). www.modot.org. May 2010. p. 5.
- "Missouri's Experience with a Diverging Diamond Interchange" (PDF). www.modot.org. May 2010. p. 6.
- "The 'Diverging Diamond' Interchange Is an Abomination - Sarah Goodyear". The Atlantic Cities. 2011-09-20. Retrieved 2014-04-22.
- "United States Patent 8,950,970: Double Crossover Merging Interchange". United States Patent and Trademark Office. February 10, 2015. Retrieved 4 October 2016.
- "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.
- "Alternative Intersections & Interchanges Symposium" (PDF). Transportation Research Board. July 21, 2014. Archived from the original (PDF) on March 5, 2016. Retrieved 4 October 2016.
- 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.
- Turner-Fairbank Highway Research Center. "Drivers' Evaluation of the Diverging Diamond Interchange". Federal Highway Administration. FHWA-HRT-07-048.
- Innovations Library (May 2010). "Missouri's Experience with a Diverging Diamond Interchange: Lessons Learned" (PDF). Missouri Department of Transportation.
- Chlewicki, Gilbert (2003). "New Interchange and Intersection Designs: The Synchronized Split-Phasing Intersection and the Diverging Diamond Interchange" (PDF). Archived from the original (PDF) on October 20, 2011. Retrieved October 20, 2009.
- Chlewicki, Gilbert (December 4, 2011). "About Chlewicki". The Diverging Diamond Interchange Website. Retrieved January 20, 2012.
|Wikimedia Commons has media related to Diverging diamond interchange.|
- 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 Simualtion software modeling a Double Crossover Diamond Interchange
- Diverging Diamond Interchange Visualization, Instructional video on how to drive in a DDI, NCDOTcommunications, published on 10 March 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)