A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a subset of

diamond interchange A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road. Design The freeway itself is grade separation, grade-separated from the minor road, one crossing the other over a bridge. ...

in which the opposing directions of travel on the non-

freeway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway, and expressway. Other similar terms ...

road cross each other on either side of the interchange so that traffic crossing the freeway on the overpass or underpass is operating on the opposite driving side from that which is customary for the jurisdiction. The crossovers may employ one-side overpasses or be at-grade and controlled by

traffic light Traffic lights, traffic signals, or stoplights – also known as robots in South Africa, Zambia, and Namibia – are signaling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order t ...

s. The diverging diamond interchange has advantages in both efficiency and safety, and was cited by ''

Popular Science Popular science (also called pop-science or popsci) is an interpretation of science intended for a general audience. While science journalism focuses on recent scientific developments, popular science is more broad ranging. It may be written ...

'' as one of the best engineering innovations of 2009 and in the U.S. has been promoted as part of the Federal Highway Administration's Every Day Counts initiative. The flow through a diverging diamond interchange using overpasses at the crossovers is limited only by

weaving Weaving is a method of textile production in which two distinct sets of yarns or threads are interlaced at right angles to form a fabric or cloth. Other methods are knitting, crocheting, felting, and braiding or plaiting. The longitudinal ...

, and the flow through an implementation using traffic lights is subject to only two clearance intervals (the time during which all lights are red so that the intersection may fully clear) per cycle. The greatest safety concern of the interchange stems from its relative rarity, as drivers instinctively trying to stay on the customary side of the road could use the crossover intersections to turn against the posted direction of travel. This is a rare occurrence; it is possible only when traffic is so sparse that no cars from the oncoming direction are stopped at the light, and clear signage further reduces the likelihood of such errors.

History

Interstate 44 and Route 13 diverging diamond interchange

The first known diverging diamond interchanges were in France in the communities of

Versailles The Palace of Versailles ( ; ) is a former royal residence commissioned by King Louis XIV located in Versailles, Yvelines, Versailles, about west of Paris, in the Yvelines, Yvelines Department of Île-de-France, Île-de-France region in Franc ...

( A13 at D182),

Le Perreux-sur-Marne Le Perreux-sur-Marne (, ) is a Communes of France, commune in the Val-de-Marne Departments of France, department in the eastern suburbs of Paris, France. It is located from the Kilometre Zero, center of Paris. History The commune of Le Perreux-s ...

( A4 at N486) and Seclin ( A1 at D549), all built in the 1970s. However, a three way derivative was built in the UK on the M1 to provide access to London Gateway services (formerly Scratchwood Services) in 1969. The ramps of the first two have since been reconfigured to accommodate ramps of other interchanges, but they continue to function as diverging diamond interchanges. The interchange in Seclin (at ) between the A1 and Route d'Avelin was somewhat more specialized than in the adjacent diagram: 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. In the United States, invention of the diverging diamond interchange is credited to Gilbert Chlewicki. In 2005, the

Ohio Department of Transportation The Ohio Department of Transportation (ODOT; ) is the administrative department of the government of Ohio, Ohio state government responsible for developing and maintaining all state and U.S. roadways outside of municipalities and all List of In ...

(ODOT) considered reconfiguring the existing interchange on

Interstate 75 Interstate 75 (I-75) is a major north–south Interstate Highway in the Great Lakes and Southeastern regions of the United States. As with most Interstates that end in 5, it is a major cross-country, north–south route, traveling from S ...

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 The Missouri Department of Transportation (MoDOT, ) is a state government organization in charge of maintaining public roadways of the U.S. state of Missouri under the guidance of the Missouri Highways and Transportation Commission (MHTC). MoDOT ...

(MoDot) was the first US agency to construct one, in Springfield at the junction between

I-44 Interstate 44 (I-44) is an Interstate Highway in the central United States. Although it is nominally an east–west road as it is even-numbered, it follows a more southwest–northeast alignment. Its western terminus is in Wichita Falls, T ...

and

Missouri Route 13 Route 13 is a highway in Missouri which runs almost the entire north–south length of the state. Its northern terminus is at U.S. Route 69 (Missouri), U.S. Route 69/U.S. Route 136 (Missouri), 136 in Bethany, Missouri, Bethany. Its south ...

(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. MoDot reports that traffic congestion for left turns at the intersection cleared up immediately, and crashes dropped by 40–50%. In 2010, the

Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program a ...

released a publication titled "Alternative Intersections/Interchanges: Informational Report (AIIR)" with a chapter dedicated to this design. Additional research was conducted by a partnership of the

Virginia Polytechnic Institute and State University The Virginia Polytechnic Institute and State University, commonly referred to as Virginia Tech (VT), is a Public university, public Land-grant college, land-grant research university with its main campus in Blacksburg, Virginia, United States ...

and the Turner-Fairbank Highway Research Center and published by Ohio Section of the

Institute of Transportation Engineers The Institute of Transportation Engineers (ITE) is an international educational and scientific association of transportation professionals who are responsible for meeting mobility and safety needs. ITE facilitates the application of technology and ...

. On August 14, 2011, the

Kentucky Transportation Cabinet The Kentucky Transportation Cabinet (KYTC) is Kentucky's state-funded government agency, agency charged with building and maintaining U.S. Highway System, federal highways and List of primary state highways in Kentucky, Kentucky state highways, ...

(KYTC) completed conversion of the intersection of U.S. Route 68 and Kentucky Route 4 in Lexington to a diverging diamond design, the first in the state and the sixth completed nationally.

Stantec Stantec Inc. is an international professional services company in the design and consulting industry. The company was founded in 1954, as ''D. R. Stanley Associates'' in Edmonton, Alberta, Canada. Stantec provides professional consulting servi ...

, the engineers who completed the upgrades to the interchange, noted the solution while providing substantial cost savings over other possible options also has decreased accidents by 45 percent, improved traffic flow to more than 35,000 vehicles per day, and incorporated KYTC's goal to provide new paths for bicycles and pedestrians through the area. That same day in Highland, Utah the seventh U.S. diverging diamond interchange opened at the intersection of

I-15 I15 may refer to: * Interstate 15, a north–south Interstate Highway in the United States of America * Polikarpov I-15, a Soviet fighter aircraft * I15 (band), a band * , of the Imperial Japanese Navy * Älvsborg Regiment The Älvsborg Regiment ...

and Timpanogos Highway. According to the

U.S. Department of Transportation The United States Department of Transportation (USDOT or DOT) is one of the executive departments of the U.S. federal government. It is headed by the secretary of transportation, who reports directly to the president of the United States a ...

the goals of this intersection upgrade were similar, increasing traffic capacity and improved pedestrian and bicycle access while reaching these goals without requiring substantial revisions to the existing interstate overpass. Quoting a June 2014 USDOT publication, "the DDI has made travel more efficient and accessible for all users." The year 2016 saw the introduction of diverging diamond interchanges by three states. In February, the

Oregon Department of Transportation The Oregon Department of Transportation (ODOT) is a department of the state government of the U.S. state of Oregon responsible for systems of transportation. It was first established in 1969. It had been preceded by the Oregon State Highway De ...

opened one in Phoenix. In October, the

New Mexico Department of Transportation The New Mexico Department of Transportation (NMDOT; ) is a state government organization which oversees transportation in New Mexico, State of New Mexico in the southwestern United States. The agency has four main focuses—transit, rail, av ...

converted the crossing of NM 14 (Cerrillos Road) and

Interstate 25 Interstate 25 (I-25), also known as the Pan-American Freeway, is a major Interstate Highway in the western United States. It is primarily a north–south highway, serving as the main route through New Mexico, Colorado, and Wyoming. I-25 st ...

in Santa Fe. In November, the

Delaware Department of Transportation The Delaware Department of Transportation (DelDOT) is an agency of the U.S. state of Delaware. The Secretary of Transportation is Shanté Hastings. The agency was established in 1917 and has its headquarters in Dover, Delaware, Dover. The depar ...

completed the conversion of the DE-1 and DE-72 (Wrangle Hill Rd) overpass west of

Delaware City Delaware City is a city in New Castle County, Delaware, United States. The population was 1,885 as of 2020. It is a small port town on the eastern terminus of the Chesapeake and Delaware Canal and is the location of the Forts Ferry Crossing to ...

. The first interchange in Canada opened on August 13, 2017, at

Macleod Trail Macleod Trail is a major road in Calgary, Alberta. It is a six- to eight-lane principal arterial road extending from downtown Calgary to the south of the city, where it merges into Alberta Highway 2, Highway 2. South of Anderson Road, Macleod Tr ...

and 162 Avenue South in

Calgary Calgary () is a major city in the Canadian province of Alberta. As of 2021, the city proper had a population of 1,306,784 and a metropolitan population of 1,481,806 making it the third-largest city and fifth-largest metropolitan area in C ...

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

followed by one east of

Regina, Saskatchewan Regina ( ) is the capital city of the Provinces and territories of Canada, Canadian province of Saskatchewan. The city is the second-largest in the province, and is a commercial centre for southern Saskatchewan. As of the 2021 Canadian census, ...

the next year as part of the Regina Bypass project. The first diverging diamond interchange in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

opened to traffic by the Queensland Department of Transport and Main Roads on November 28, 2019. The interchange, located in Caloundra, Queensland, connects Caloundra Road to the

Bruce Highway The Bruce Highway is a major highway in Queensland, Australia. Commencing in the state capital, Brisbane, it passes through areas close to the eastern coast on its way to Cairns in Far North Queensland. The route is part of the Australian Natio ...

. The former interchange was upgraded and converted as part of the larger Bruce Highway Upgrade Program. In December 2019, the

Virginia Department of Transportation The Virginia Department of Transportation (VDOT) is the agency of the U.S. state, state government responsible for transportation in the state of Virginia in the United States. VDOT is headquartered at the Virginia Department of Highways Buildin ...

completed the conversion of the interchange at Courthouse Road and I-95 in Stafford, VA into a diverging diamond interchange. In 2020, the

California Department of Transportation The California Department of Transportation (Caltrans) is an Executive (government), executive department of the U.S. state of California. The department is part of the Government of California#State agencies, cabinet-level California State Tran ...

(Caltrans) completed the first diverging diamond interchange in

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. An interchange at State Route 120 and Union Road in

Manteca, California Manteca is a city in San Joaquin County, California. The city had a population of 83,498 as of the 2020 United States census, 2020 Census. It is part of the Stockton-Lodi, CA Metropolitan Statistical Area. History Manteca is a city in the Ce ...

was converted to this interchange and opened to traffic on November 25.

Use

Operational

, over 160 DDIs were operational across the world including: * 3 in Australia, with more planned * 1 in Belgium * 3 in Canada * 1 in Denmark, opened September 17, 2017 * 2 in France, built in 1970s * 8 in Malaysia * 2 in Saudi Arabia * 2 in South Africa * 1 in the United Arab Emirates * 1 in Costa Rica * >150 in the United States, with ~80 more under construction

Advantages

Compared to a

, the advantages of a diverging diamond interchange are: * 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 by removing the need for turn lanes. * Costs significantly less than a normal interchange.

Disadvantages

* 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 must be 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 * Some factors make turning left onto a diverging diamond interchange from the highway ramp more hazardous: 1) There is a yield sign instead of a traffic light. 2) The driver can not see if the light for the through traffic is red or green. 3) The visible distance to see the oncoming through traffic from that vantage is very short. All of these combined results in the driver entering a potentially very busy interchange without sufficient information.

Further considerations

* 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 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 A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two controlled-access highways that allows for free-flowing movement to and from all directions of traffic. These interchanges e ...

. It eliminates the disadvantages of weaving and of merging into the outside lane from which the standard DDI variation suffers. A highway U-turn requires weaving, however. As of 2016, no such interchanges have been constructed.

Three-level diverging diamond interchange

Another variation of the diverging diamond was developed by the Arizona Department of Transportation (ADOT) as part of their

I-10 Interstate 10 (I-10) is the southernmost transcontinental highway in the Interstate Highway System of the United States. It is the fourth-longest Interstate in the country at , following I-90, I-80, and I-40. It was part of the originall ...

widening/ SR 210 extension project near

Tucson, Arizona Tucson (; ; ) is a city in Pima County, Arizona, United States, and its county seat. It is the second-most populous city in Arizona, behind Phoenix, Arizona, Phoenix, with a population of 542,630 in the 2020 United States census. The Tucson ...

. The interchange (I-10 exit 270 at Kolb Road) will be reconfigured as a combination of both a diverging diamond and a three-level diamond interchange. The ramps (the top level/Kolb Road) would carry thru traffic while the diverging diamond (the second level/interchange) would be for traffic getting on or off the freeway (the third level/I-10).

References

External links

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 Simulation 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)

Examples

* —Diverging diamond in

, France * Diverging diamond in Seclin,

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...