Diverging diamond interchange
||The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject. (December 2013)|
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 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".
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 left turns must clear opposing traffic and all movements are discrete, with most controlled by traffic signals.
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.
Some of the intersections in the design can be unsignalized. The left turn from the freeway off-ramp, for example, can form an auxiliary lane that then becomes an exit-only lane for the entrance ramp to the freeway in the opposite direction. Omitting the traffic signals for the left turn movements off the freeway only works well with single left turns and when short queues exist within the interchange on the arterial street.
Prior to 2009 the only known diverging diamond interchanges were in France in the communities of Versailles, Le Perreux-sur-Marne, and Seclin, all built in the 1970s. (The ramps of the first two listed have been reconfigured to accommodate ramps of other interchanges, as seen in views on the Google Earth and Google Maps websites, but they continue to function as diverging diamond interchanges.) The interchange configuration was introduced to America in a paper submitted to the 2nd Urban Street Symposium held in Anaheim, California in 2003 by Gilbert Chlewicki, a civil engineer from Baltimore, Maryland.
The Missouri Department of Transportation was the first in the United States to construct a diverging diamond interchange, in Springfield at the intersection of I-44 and Missouri Route 13 (at ). Construction began the week of January 12, 2009, and the interchange opened on Sunday, 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 appears to have been made 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, the Turner-Fairbank Highway Research Center and a private consultant, and the results were published by Ohio Section of the Institute of Transportation Engineers. The Federal Highway Administration has released a publication titled "Alternative Intersections/Interchanges: Informational Report (AIIR)"  with a dedicated chapter to this design.
- Provides for two-phase signals with short cycle lengths, significantly reducing delay.
- Reduced horizontal curvature reduces risk of off-road crashes.
- Increases the capacity of turning movements to and from the ramps.
- May potentially reduce the number of lanes on the crossroad, minimizing impacts to existing right-of-way.
- Substantially reduces the number of conflict points, thus theoretically improving safety.
- Theoretically improves pedestrian safety.
- Increases the capacity of an existing overpass or underpass, by removing the need for turn lanes.
- Drivers may not be familiar with configuration, particularly with regards to merging maneuvers along the left side of the roadway or the crossover flow of traffic.
- Pedestrians would be required to cross free-flowing traffic on freeway ramps. 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—unless the two signalized intersections are replaced with underpass/overpass structures (an expensive proposition and usually not possible within the existing right of way of the non-freeway road) - see "Double crossover merging interchange" below.
- Exiting traffic cannot re-enter the freeway in the same direction without first leaving the interchange on the crossroad. This has several implications:
- It makes it difficult to implement stops for express transit buses.
- Drivers who accidentally take the wrong exit must turn around somewhere along the crossroad.
- Emergency management cannot use the exit and entrance ramps to allow freeway traffic to bypass a crash at the bridge.
- An oversize load can not use the exit and entrance ramps to bypass a bridge that is too low.
- A diverging diamond can not be the parent interchange for a rebound interchange without using collector-distributor roads (local-express lanes).[clarification needed]
- No standards currently exist for this design and the design is extremely dependent on site-specific conditions.
- There is no crash history available in the North America region, as no DDIs existed in North America until June 21, 2009, when North America's first DDI opened to traffic in Springfield, Missouri.
- 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.
A free-flowing variation on the diverging diamond interchange, which could also be used as a junction between two freeways, could be created by replacing the traffic lights with bridges. Some of the disadvantages of this design would be added weaving movements and traffic merging into the outside (high-speed) lane. It is not known whether any such interchanges have been constructed.
Double crossover merging interchange
There is also a free-flowing design, for which a patent has been applied, called the "double crossover merging interchange" (DCMI), which includes elements from the diverging diamond interchange, the standard 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. It is not known whether any DCMI interchanges have been constructed.
The lane configuration allows for high capacity free-flow traffic without the need for costly elevated "flyover" roadway bridges, and uses less lane area and structures than an interchange with large radius flyover(s). The DCMI employs several of the design techniques of the DDI. The DCMI also has similarities to a standard diamond interchange and to a stack interchange.
The DCMI has several distinct design features that differentiate it from a diverging diamond interchange. Utilizing a standard main bridge with two smaller underpass type bridges on either side of the main bridge, the DCMI lets vehicles cross over conflicting traffic streams while removing weaving maneuvers. This configuration produces an interchange with merging maneuvers. By placing two smaller bridges (grade separation) on either side of the main bridge, the traffic signals can be eliminated. Additionally, off-ramp traffic can be crossed over on the same smaller side bridges used by the main traffic patterns. Hence, this removes conflicts that would take place with an at-grade traffic signal. The key feature of this type of design is not only the elimination of the conflicts that occur at-grade, but also allowing the off-ramp traffic to cross over without the need for lane changes or weaving within the interchange.
The double crossover merging interchange introduces a number of new mechanisms to a tight diamond type interchange while producing a free-flow traffic environment interchange.
It is not known whether any such interchanges have been constructed.
- No weaving sections
- Provides free-flow operations
- Reduced vehicle emissions (no idling vehicles)
- No right-angle crossing conflicts
- No delay incurred due to traffic signals
- Less costly to construct than a full free-flow interchange with flyover roadway bridges
- May be more costly than a standard diamond or diverging diamond interchange to construct
- Standard diamond interchange
- Single-point urban interchange (SPUI)
- Continuous-flow intersection
- Hook turn
- Michigan left
- Hughes, Warren; Jagannathan, Ram. "Double Crossover Diamond Interchange". Federal Highway Administration date= October 2009. FHWA-HRT-09-054. Retrieved April 22, 2012.
- "Gallery: Looking Back at the 100 Best Innovations of 2009". Popular Science. Retrieved January 20, 2012.
- "Diverging Diamond Interchange". OHM Advisors.
- VirginiaDoT: I-64 Interchange at Route 15, Zion Crossroads, modified 13 June 2013, accesed 11 December 2013
- Chlewicki, Gilbert (2003). "New Interchange and Intersection Designs: The Synchronized Split-Phasing Intersection and the Diverging Diamond Interchange" (PDF). Retrieved October 20, 2009.
- Chlewicki, Gilbert (December 4, 2011). "About Chlewicki". The Diverging Diamond Interchange Website. Retrieved January 20, 2012.
- "I-44/Route 13 Interchange Reconstruction: Diverging Diamond Design". Missouri Department of Transportation. April 2009. Retrieved May 19, 2009.
- "Public Meeting Tuesday, June 24, On I-44/Route 13 Reconstruction To Reduce Congestion, Improve Safety" (Press release). Missouri Department of Transportation. June 19, 2008. Retrieved June 19, 2008.
- Edara, Praveen K.; Bared, Joe G. & Jagannathan, Ramanujan. "Diverging Diamond Interchange and Double Crossover Intersection: Vehicle and Pedestrian Performance" (PDF).
- Patent US 20130011190 A1 (WO 2013009704 A1): Double crossover merging interchange, published January 10, 2013
- WO application 2013009704, Gingrich, Michael A., Sr., "Double crossover merging interchange", published 2013-01-17, assigned to Gingrich, Michael A., Sr.
- "Alternative Intersections/Interchanges: Informational Report (AIIR)". Federal Highway Administration.
- http://www.DcmiInterchange.com Double Crossover Merging Interchange.
- Gingrich, Michael A., Sr. (June 2011). "DCMI (Double Crossover Merging Interchange)" (PDF). Institute of Transportation Engineers. Retrieved January 23, 2013.
- Hamilton, Grant (March 4, 2012). "35 years to upgrade the highway?". Brandon Sun. Retrieved January 23, 2013.
- 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.
- Utah Department of Transportation Timpanogos Highway Diverging Diamond Interchange animation video
- Transportation engineers discuss the design of the fifth U.S. DDI in Alcoa, TN
- Video of Double Crossover Diamond Interchange (new name for DDI) in Lexington, Kentucky.
- Video of Paramics Traffic Simualtion software modeling a Double Crossover Diamond Interchange
- Images of Diverging Diamond Interchange in Springfield, Missouri the first in North America.
- Animation of diverging diamond interchange at Dorsett and Interstate 270 in St. Louis.
- Web page for Springfield Missouri Diverging Diamond Interchange
- Web page for Missouri DDI at I-435 and Front st.
- Versailles, France Map of a diverging diamond interchange in
- Le Perreux-sur-Marne, France Map of a diverging diamond interchange in
- Seclin, France Map of a diverging diamond interchange in