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 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 located in France in the communities of Versailles, Le Perreux-sur-Marne, and Seclin (see External Links, below). (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. In 2009 an interchange of this type was constructed in Springfield, Missouri with additional interchanges constructed in North America in subsequent years(see below).
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 reversed 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).
- 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).
Further considerations 
- 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.
Use in North America 
The Missouri Department of Transportation was the first in the United States to construct a diverging diamond interchange, in Springfield, Missouri at the intersection of I-44 and MO-13 (at ) 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.
MoDOT completed a second diverging diamond interchange in Springfield at U.S. 60 and National Avenue in July 2010.
Other Missouri diverging diamond interchanges can be found at:
- I-270 and Dorsett Road in St. Louis County (completed in late 2010).
- I-435 and Front Street in Kansas City on November 7, 2011.
- US 65 and Missouri Route 248 (Shepherd of the Hills Expressway)/US Business 65 (Branson Landing Boulevard) on November 20, 2011, in Branson, Missouri.
- US 67 and Missouri Route 221 in Farmington.
- US 65 and Chestnut Expressway in Springfield (completed November 2012).
In Lehi, Utah, a suburb of Provo, North America's seventh diverging diamond interchange opened on August 15, 2011, at the Timpanogos Highway (SR-92) exit of I-15. This was the first attempt in Utah to reconfigure an interchange to a diverging diamond using existing infrastructure.
In Salt Lake City's western outskirts, North America's eighth diverging diamond interchange opened on October 23, 2011, at the Bangerter Highway (SR-154) exit of SR-201. As with the Lehi diverging diamond, existing infrastructure was modified to reconfigure the interchange.
Utah opened another diverging diamond on November 7, 2011, at 500 East in American Fork—also a Provo suburb—as part of the reconstruction of I-15. This was the fourth diverging diamond in Utah, and the ninth in the US.
Other states 
In Hanover, Maryland, construction began on May 1, 2012, to reconfigure an existing interchange into a diverging diamond interchange, to help traffic flow between the Baltimore-Washington Parkway and Arundel Mills Boulevard, the primary route to Arundel Mills Mall and the Maryland Live! casino. The reconfigured interchange opened on June 11, 2012, just days after the opening of the casino.
Nevada's first diverging diamond interchange was opened by the Nevada Department of Transportation on November 21, 2012 in Reno at Interstate 580 / U.S. Route 395 and Moana Lane (Exit 64).
In Brighton, Monroe County, New York, just south of Rochester, a diverging diamond interchange at Interstate 590 and South Winton Road opened on September 11, 2012. It was the first diverging diamond in New York.
There is a sort of half-diverging-diamond interchange between Interstate 95 and Thurbers Avenue in Providence, Rhode Island, (at ). The extension of Thurbers Avenue to US Route 1 being a one-way prevents it from being a full diverging diamond, but the interchange directly with Route 1 keeps almost full functionality, lacking only an easy-access interchange from US 1 to I-95 South.
The Tennessee Department of Transportation designed a diverging diamond as part of the US 129 Bypass / Bessemer St / Middlesettlements Rd Interchange in Alcoa. The interchange opened on December 12, 2010, becoming the fifth operational diverging diamond in the country.
Future use in North America 
- In May 2012, funds were committed for a preliminary design of a diverging diamond interchange in Boulder County, Colorado for the US 36/McCaslin Boulevard interchange connecting the town of Superior and the city of Louisville.
- In late December 2012, funding was secured for a diverging diamond on the western edge of Grand Junction, Colorado in Mesa County at exit 26 on Interstate 70. Construction is expected to start in July 2013.
The Missouri Department of Transportation has an aggressive plan to build additional diverging diamond interchanges throughout the state. Interchanges either in construction or planning include:
- Kansas City metropolitan area:
- I-70 at Woods Chapel Road in Blue Springs
- Route 150 at Botts Road in Kansas City (this project includes both a new bridge and a diverging diamond interchange) with completion expected in early to mid-2013
- I-29 at Tiffany Springs Parkway in Kansas City
- I-49 & Route 291 in Harrisonville
Other interchanges either being built or in planning include:
Other states and provinces 
Florida is studying two locations near Sarasota, and a third farther south on I-75.
Four diverging diamonds are proposed in Georgia: at the SR 120 (Duluth Highway) bridge and interchange over SR 316 in Lawrenceville, at the SR 317 (Lawrenceville-Suwanee Road) interchange and bridge over Interstate 85 in Suwanee and at the SR 140 (Jimmy Carter Boulevard) and Pleasant Hill Road interchanges and bridges over I-85 in Gwinnett County, to the northeast of Atlanta.
The Idaho Transportation Department is constructing a diverging diamond interchange to replace the existing U.S. Route 91 interchange on Interstate 86, in Chubbuck, near Pocatello. Construction is slated to finish in 2015.
In 2009, the Indiana Department of Transportation announced plans to build a diverging diamond interchange near Watson, Indiana, in Clark County, as part of the Ohio River Bridges Project. It will replace the current interchange at SR 265 and SR 62. The engineering for this project is almost completed. Another diverging diamond is being studied north of Fort Wayne, Indiana, at Interstate 69 and SR 1. A diverging diamond is one of the designs being considered for the proposed interchange between Interstate 65 and Worthsville Road near Greenwood.
The Kansas Department of Transportation is currently working with Burns & McDonnell Engineering Company to design a diverging diamond Interchange for a new interchange on I-35 at Homestead Lane in Johnson County Kansas.
This type of interchange was studied and rejected for use in Maryland along the Baltimore-Washington Parkway in Anne Arundel County, near the Baltimore-Washington International Thurgood Marshall Airport.
A diverging-diamond interchange is nearing completion for the future interchange at US Hwy 52 and Olmsted County Rd. 12 in Pine Island, Minnesota, just a few miles north of the city of Rochester. It will be the first diverging-diamond in Minnesota. Two other projects are being studied, one in Sartell, near St. Cloud, and the other near Elko.
On April 6, 2010, the Charlotte suburb of Cornelius approved plans by the North Carolina Department of Transportation to convert the existing diamond interchange into a diverging diamond at the West Catawba/Catawba Exit (#28). This will be the first one in the state of North Carolina. Work is expected to finish by 2012. North Carolina has also designed three other diverging diamonds in the Charlotte area, two on I-85 and one on I-485, and is studying diverging diamonds at Asheville, Kernersville, Lumberton, and Leland, for a total of eight projects in North Carolina. Construction for the first DDI in North Carolina's Triad region is underway at I-40 and Union Cross Road in Winston-Salem.
The Ohio Department of Transportation (ODOT) has considered employing the interchange. ODOT planned to reconstruct the I-75/US-224/SR-15 interchange in Findlay to this configuration, but reconsidered. The agency similarly considered using the configuration for the I-480/Tiedeman Road interchange in Brooklyn, but decided to widen the existing ramps instead. In October 2012, ODOT announced plans to use the configuration for the rebuild of the I-270/Roberts Road exit on the west side of Columbus. Construction began in May 2013.
In February 2007, the Oregon Department of Transportation accepted the DDI as the preferred alternative at Exit 24 (Fern Valley Road) along I-5 in Phoenix, in the southern area of Oregon. It will begin construction in 2012. A second diverging diamond interchange is being studied for Ashland.
The Pennsylvania Department of Transportation is designing a diverging diamond interchange at the junction of I-70/I-79 and U.S. Route 19 in South Strabane Township near Washington. It also has two projects under study: US 222 and Broadcasting Road at Reading, and US 222 and US 322 near Ephrata.
In Sioux Falls, South Dakota in 2010, during a public forum revealing the information yielded from study of the 41st Street corridor from Marion Road to Kiwanis Avenue, city planners proposed the reconstruction of the 41st Street interchange at Interstate 29 (Exit 77) into a diverging diamond interchange.
A diverging diamond intersection is planned for Exit 407 of Interstate 40 at Tennessee State Route 66 in Sevier County, Tennessee just outside of Knoxville, Tennessee to relieve traffic congestion at a major access point to the Great Smoky Mountains National Park. This will be the second diverging diamond interchange in Tennessee.
The Virginia Department of Transportation has proposed to reconstruct the 0.49 mile stretch of U.S. Route 15 where it meets Interstate 64 at Zion Crossroads as a diverging diamond interchange. VDOT anticipates construction to begin in 2012. VDOT also proposes constructing a diverging diamond interchange at the intersection of U.S. 460 and Southgate Drive in Blacksburg, replacing the only remaining at-grade intersection on the freeway-standard bypass of Blacksburg and Christiansburg. In March 2013, VDOT approved plans to modify the existing interchange of I-581 and Valley View Boulevard in Roanoke to become a diverging diamond. Construction is expected to begin in fall 2013, with completion expected in mid-2016.
Similar interchanges 
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 proposed design called a 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.
||This section may contain original research. (July 2012)|
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
See also 
- Standard diamond interchange
- Single-point urban interchange (SPUI)
- Continuous-flow intersection
- Hook turn
- Michigan left
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- NYSDOT - I590 Winton Road Interchange
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Further reading 
- "Visual and Pictures of the interchange method", urbansplatter.com, January 19, 2010
- "Drivers' Evaluation of the Diverging Diamond Interchange" (publication number FHWA-HRT-07-048). Turner-Fairbank Highway Research Center, Federal Highway Administration
- "Missouri's Experience with a Diverging Diamond Interchange: Lessons Learned, MoDOT Innovations Library, May 2010
- 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