Diverging diamond interchange


A diverging diamond interchange, also called a double crossover diamond interchange, 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 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 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 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-way, 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 in "Best of What's New 2009".
The design also is promoted as part of the Federal Highway Administration's Every Day Counts initiative which started in 2011.

History

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.
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 interchanges. Examples of this type of interchange include the intersection of Interstate 95 and I-695 north of Baltimore, and the intersection of I-20/59 and Interstate 65 in Birmingham, Alabama.
In 2005, the Ohio Department of Transportation 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. 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.
In November 2016, the Delaware Department of Transportation completed the conversion of the DE-1 and DE-72 overpass west of Delaware City, DE into a diverging diamond interchange.The interchange is viewable via live traffic camera on the .
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.
The first interchange in Canada opened on August 13, 2017, at Macleod Trail and 162 Avenue South in Calgary, Alberta. Followed by one in Regina, Saskatchewan the next year as part of the Regina Bypass project.
The interchange in Seclin 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. The Federal Highway Administration released a publication titled "Alternative Intersections/Interchanges: Informational Report " with a chapter dedicated to this design.

Usage

Operational

As of December 4, 2019, 124 DDIs were operational across the world including:
  1. Glendale Avenue interchange on the Queen Elizabeth Way in Niagara-on-the-Lake, Ontario is planned to be reconstructed as a diverging diamond interchange.
  2. The MTO is planning to reconfigure the interchange at Highway 400 and Mapleview Drive in Barrie, Ontario.
  1. The existing overpass of DE-1 and DE-72 west of Delaware City, DE was converted to a diverging diamond interchange in November 2016 with planning that began in early summer 2015.
  2. The existing interchange between FM 60 and FM 2818 at Texas A&M University in College Station, Texas is being converted to a DDI; construction began on March 6, 2017 and is expected to last 25 months, with an estimated cost of $14.1 million.
  3. The existing at-grade intersection between the Mopac Expressway and Slaughter Lane in Austin, Texas is being converted to a diverging diamond interchange; construction is ongoing and the DDI opened on November 11th, 2018. Final construction was completed in January 2019.
  4. The Interstate 5/State Route 510 interchange in Lacey, Washington will be reconstructed into a DDI, the first in the state; construction is planned to start in late 2018 and to be complete in 2020.
  5. The existing interchange at I-17 and Happy Valley Road in Phoenix, Arizona is currently being converted to a DDI. The project is projected to be finished in the fall of 2020.
  6. The existing interchange between Interstate 75 and Union Centre Boulevard in West Chester Township, Butler County, Ohio, near Cincinnati, is planned to be converted to a DDI; the project is scheduled to begin in 2019 and be completed a year-and-a-half later at a projected cost of $13 million.
  7. The existing interchange of Interstate 90 and Lacrosse Street in Rapid City, South Dakota is planned to be converted to a DDI; construction is scheduled to begin in 2020.
  8. The existing interchange of Interstate 89 and the concurrent stretch of U.S. Route 7 and U.S. Route 2 in Colchester, Vermont, near the Winooski city line, will be developed into a DDI in the spring of 2021.
  9. The existing interchange at Loop 1604 and FM 2696 in San Antonio, Texas will be converted to a DDI. Construction is currently projected to start in 2021.
  10. The existing interchange between Interstate 90 and State Route 18 in King County, Washington, near Snoqualmie, is planned to be converted to a DDI; construction is projected to start in 2021, with project completion expected in 2023.
  11. The existing interchange between I-75 and State Route 725 in Miamisburg, Ohio, near Dayton, is planned to be converted to a DDI; the project will not be built until 2023 and its projected cost is $4.1 million, entirely funded by the state.
  12. As part of the Puget Sound Gateway Program's SR 167 Completion Project in northeast Pierce County, Washington, which will complete the State Route 167 limited access freeway from Puyallup to Interstate 5, and construct a new spur route from Interstate 5 to State Route 509 at the Port of Tacoma, Tacoma, Washington, a new modified DDI will be constructed between the new SR 167 freeway, new SR 509 Spur, and Interstate 5. Construction of the first stage, which will include the DDI interchange, is planned to start in 2019 and finish sometime in 2026.
  13. The existing interchange between I-70 and North Kipling Street in Wheat Ridge, Colorado, near Denver, is planned to be converted to a DDI. As of February 2019, neither the timeline nor the cost have been established.
  14. The existing interchange at US 281 and Jones-Maltsberger Road in San Antonio, Texas will be converted to a DDI. This project has not yet been funded, so no timeline has been set.

    Advantages

A free-flowing interchange variant, patented in 2015, has received recent attention. Called the double crossover merging interchange, 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.

Examples