Diverging diamond interchange

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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.

A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD),[1] 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".[2]

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.[3]

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.

History[edit]

A diagram illustrating traffic movements in the interchange

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.[4] (The ramps of the first two have been reconfigured to accommodate ramps of other interchanges, but they continue to function as diverging diamond interchanges.)

In 2005, the Ohio Department of Transportation (ODOT) considered reconfiguring Interstate 75's existing interchange at US 224 and SR 15 west in 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.[5] By 2006, ODOT had reconsidered, instead adding lanes to the existing overpass.[6][7]

Southern 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°15′01″N 93°18′39″W / 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 Sunday, June 21, 2009.[8][9] This interchange was a conversion of an existing standard diamond interchange, and used the existing bridge.

The interchange in Seclin (at 50°32′41″N 3°3′21″E / 50.54472°N 3.05583°E / 50.54472; 3.05583) 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.

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.[10] The Federal Highway Administration released a publication titled "Alternative Intersections/Interchanges: Informational Report (AIIR)" [11] with a dedicated chapter to this design.

Advantages[edit]

  • 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.
  • 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.

Disadvantages[edit]

Plan of rejected diverging diamond interchange in Findlay, Ohio
  • 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.
  • Pedestrian access requires at least four crosswalks (two cross the two signalized lane crossover intersections, while two more cross the local road at each end of the interchange).[12] 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 reenter 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
    • A diverging diamond cannot be the parent interchange for a rebound interchange without using collector-distributor roads (local-express lanes).[clarification needed]

Further considerations[edit]

  • No standards currently exist for this design
  • The design depends on site-specific conditions.
  • North American crash history is unavailable, as no DDIs existed in North America until June 21, 2009.
  • 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.

Variants[edit]

Free-flowing[edit]

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. No known examples have been constructed.

Double crossover merging interchange[edit]

Another free-flowing design, for which a patent has been applied, called the "double crossover merging interchange" (DCMI),[13] 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.

DCMI traffic flow patterns
Three-dimensional computer generated DCMI

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).[11] The DCMI also has similarities to a standard diamond interchange and to a stack interchange.

DCMI uses a standard main bridge with two smaller bridges on either side. DCMI lets vehicles cross over conflicting traffic streams while removing weaving maneuvers. This configuration produces an interchange with merging maneuvers.[14][15] By placing two smaller bridges 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. 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.

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.

No such interchanges have been constructed.[16]

DCMI advantages[edit]

  • No weaving sections
  • Free-flow operations
  • Reduced vehicle emissions (no idling vehicles)
  • No right-angle crossing conflicts
  • No traffic signals
  • Less costly to construct than a full free-flow interchange with flyover roadway bridges

DCMI disadvantages[edit]

  • May be more costly than a standard diamond or diverging diamond.

Unsignalized[edit]

Some applications 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.

See also[edit]

References[edit]

  1. ^ Hughes, Warren; Jagannathan, Ram (October 2009). "Double Crossover Diamond Interchange". Federal Highway Administration. FHWA-HRT-09-054. Retrieved April 22, 2012. 
  2. ^ "Gallery: Looking Back at the 100 Best Innovations of 2009". Popular Science. Retrieved January 20, 2012. 
  3. ^ "Diverging Diamond Interchange". OHM Advisors. 
  4. ^ Staff (June 13, 2013). "I-64 Interchange at Route 15, Zion Crossroads". Virginia Department of Transportation. Retrieved December 11, 2013. 
  5. ^ Patch, David (May 2, 2005). "French Connection May Control Traffic Flow". The Blade (Toledo, Ohio). Retrieved April 8, 2014. 
  6. ^ Sedensky, Matt (March 30, 2006). "Missouri Drivers May Go to the Left". Star-News (Wilmington, North Carolina). Associated Press. Retrieved April 8, 2014. 
  7. ^ "Wrong Way? Not in Kansas City". Land Line Magazine. March 31, 2006. Retrieved April 8, 2014. 
  8. ^ 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. 
  9. ^ 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. 
  10. ^ Edara, Praveen K.; Bared, Joe G. & Jagannathan, Ramanujan. "Diverging Diamond Interchange and Double Crossover Intersection: Vehicle and Pedestrian Performance" (PDF). 
  11. ^ a b Hughes, Warren; Jagannathan, Ram; Sengupta, Dibu & Hummer, Joe (April 2010). Alternative Intersections/Interchanges: Informational Report (AIIR) (Report). Federal Highway Administration. http://www.fhwa.dot.gov/publications/research/safety/09060/.
  12. ^ "The 'Diverging Diamond' Interchange Is an Abomination - Sarah Goodyear". The Atlantic Cities. 2011-09-20. Retrieved 2014-04-22. 
  13. ^ (A1) US 2013011190 (A1), Gingrich, Michael A., Sr., "Double Crossover Merging Interchange", published January 10, 2013, assigned to Gingrich, Michael A., Sr. 
    WO application 2013009704, Gingrich, Michael A., Sr., "Double Crossover Merging Interchange", published January 17, 2013, assigned to Gingrich, Michael A., Sr. 
  14. ^ "Double Crossover Merging Interchange". 
  15. ^ Gingrich, Michael A., Sr. (June 2011). "DCMI (Double Crossover Merging Interchange)" (PDF). Institute of Transportation Engineers. Retrieved January 23, 2013. 
  16. ^ Hamilton, Grant (March 4, 2012). "35 Years to Upgrade the Highway?". Brandon Sun. Retrieved January 23, 2013. 

Further reading[edit]


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