A single-point urban interchange (SPUI, or ), also called a single-point interchange (SPI) or single-point diamond interchange (SPDI), is a type of
highway interchange. The design was created in order to help move large volumes of traffic through limited amounts of space efficiently.
Description

A SPUI is similar in form to a
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. ...
but has the advantage of allowing opposing left turns to proceed simultaneously by compressing the two intersections of a diamond into one single intersection over or under the free-flowing road.
The term "single-point" refers to the fact that all through traffic on the arterial street, as well as the traffic turning left onto or off the interchange, can be controlled from a single set of
traffic signal
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. Due to the space efficiency of SPUIs relative to the volume of traffic they can handle, the interchange design is used extensively in the reconstruction of existing freeways as well as constructing new freeways, particularly in dense urban environments.
Sometimes a SPUI will allow traffic to proceed straight through from the offramp to the onramp; this usually happens when the ramps connect with
frontage road
A frontage road (also known as an access road, outer road, service road, feeder road, or parallel road) is a local road running parallel to a higher-speed, limited-access road. Where parallel high-speed roads are provided as part of a maj ...
s. Since most through traffic travels over or under the intersection, the SPUI is still much more efficient than a surface intersection.
Advantages
The most commonly cited advantages of SPUIs are improved operation efficiency and safety as well as reduced right-of-way requirements compared to other interchange forms.
Left-turning traffic from both directions of the intersecting roadways is able to turn simultaneously without crossing the path of the opposing left turns. Because traffic passing through the interchange can be controlled by a single signal, vehicles can clear the intersection much more quickly than in a diamond interchange (which requires two sets of traffic signals).
SPUIs also allow for wider turns, easing movement for large vehicles, such as trucks and RVs. Furthermore, a SPUI takes up considerably less space than a full
cloverleaf interchange
A cloverleaf interchange is a two-level interchange (road), interchange in which all turns are handled by slip roads. To go left (in right-hand traffic; reverse directions in left-driving regions), vehicles first continue as one road passe ...
, allowing construction to take place on a limited amount of property and minimizing state use of
eminent domain
Eminent domain, also known as land acquisition, compulsory purchase, resumption, resumption/compulsory acquisition, or expropriation, is the compulsory acquisition of private property for public use. It does not include the power to take and t ...
.
Finally, SPUIs are reportedly safer than other space-efficient interchange forms, such as (standard) diamond interchanges. Research suggests that, although there may not be a significant difference between the two types of interchanges in terms of total collisions, the injury and fatality rates are notably lower for SPUIs than diamond interchanges.
Disadvantages
The major disadvantage of SPUIs over other types of road junctions is the increased cost due to the need for a longer or wider bridge. A freeway-under SPUI (as in the upper diagram) requires a wider bridge over the free-flowing road to make room for the compressed on- and offramps. However, this disadvantage poses less of a problem in cases where the arterial, or nonfreeway road, already requires a very wide bridge. The intersection of
97 Street, having seven throughlanes, with
Yellowhead Trail in
Edmonton
Edmonton is the capital city of the Provinces and territories of Canada, Canadian province of Alberta. It is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Central Alberta ...
, Alberta, Canada, though a diamond interchange in concept, required such a wide bridge that traffic-signal phasing allows this intersection to behave as a SPUI. A freeway-over SPUI (as in the lower photo) requires a longer bridge of the free-flowing road to cross the wider area required for the SPUI intersection below.
Because vehicles must be able to cross the pavement in six different ways, a SPUI generally has a very large area of uncontrolled pavement in the middle of the intersection. This can be unsafe particularly if drivers are unfamiliar with the interchange type. Drivers making a left turn may become confused as oncoming turning traffic passes them on the ''righthand'' side.
Due to the large intersection area, the traffic lights need a longer yellow and red phase to clear the intersection, and, even then, it may not be long enough for a bicyclist entering on green or yellow to make it across before opposing traffic gets a green.
[ In general, SPUI designs should not be used where bicycle traffic is expected unless fairly substantial changes to the design or special accommodations are provided.]
Pedestrians are usually not able to get through the intersection with one green light. It can take up to four cycles to walk through the entire length of a SPUI.
Finally, SPUIs can be somewhat difficult to clear of snow. The large area in which lanes cross may have to be shut down to allow efficient and thorough cleaning lest a snowplow leave piles of snow, interfering with traffic and visibility in the middle of the uncontrolled pavement. Additionally, if the wide area of uncontrolled pavement is on a bridge, as in the diagram, the snow cannot be pushed to the sides of the bridge as it may pose a hazard to the road underneath. This problem can be exacerbated by the comparatively large bridge width required by the SPUI.
Given that a SPUI allows only left and right turns, drivers may not reenter the freeway they are departing (if, for example, they realize that they have taken the wrong exit) within a SPUI.
Three-phase traffic signals are required. Other interchange types designed for efficiency, such as the six-ramp partial cloverleaf and the diverging diamond, require just two signal phases.
History
The first SPUI opened on February 25, 1974, along U.S. Route 19 ( State Road 55), which goes over State Road 60 east of Clearwater, Florida
Clearwater is a city and the county seat of Pinellas County, Florida, United States, west of Tampa, Florida, Tampa and north of St. Petersburg, Florida, St. Petersburg. To the west of Clearwater lies the Gulf of Mexico and to the southeast lies T ...
. It was designed by Wallace Hawkes, Director of Transportation Engineering at J. E. Greiner Company (later URS Corporation
URS Corporation (formerly United Research Services) was an engineering, design, and construction firm and a U.S. federal government contractor. Headquartered in San Francisco, California, URS was a full-service, global organization with office ...
), who has been called the "granddaddy of the urban interchange". This design has since been altered to include frontage road
A frontage road (also known as an access road, outer road, service road, feeder road, or parallel road) is a local road running parallel to a higher-speed, limited-access road. Where parallel high-speed roads are provided as part of a maj ...
s in each direction.
Several SPUIs, built in the 1970s and later, are located on German autobahns, like the A40, A42, A44, A46, A57, A59, and A113 in Berlin
Berlin ( ; ) is the Capital of Germany, capital and largest city of Germany, by both area and List of cities in Germany by population, population. With 3.7 million inhabitants, it has the List of cities in the European Union by population withi ...
. There is also a SPUI on the ''Frankenschnellweg'', the urban part of the A73, and Maximilianstraße, in Nuremberg
Nuremberg (, ; ; in the local East Franconian dialect: ''Nämberch'' ) is the Franconia#Towns and cities, largest city in Franconia, the List of cities in Bavaria by population, second-largest city in the States of Germany, German state of Bav ...
(at ). Smaller versions of the SPUI can also be found on non-autobahn roads in German cities, with right-turning traffic under signal control, located in Heilbronn
Heilbronn () is a List of cities and towns in Germany, city in northern Baden-Württemberg, Germany, surrounded by Heilbronn (district), Heilbronn District.
From the late Middle Ages on, it developed into an important trading centre. At the begi ...
, Karlsruhe
Karlsruhe ( ; ; ; South Franconian German, South Franconian: ''Kallsruh'') is the List of cities in Baden-Württemberg by population, third-largest city of the States of Germany, German state of Baden-Württemberg, after its capital Stuttgart a ...
, Sindelfingen
Sindelfingen ( Swabian: ''Sendlfenga'') is a city in Baden-Württemberg in south Germany. It lies near Stuttgart at the headwaters of the Schwippe (a tributary of the river Würm), and is home to a Mercedes-Benz assembly plant. The current mayor ...
, Stuttgart
Stuttgart (; ; Swabian German, Swabian: ; Alemannic German, Alemannic: ; Italian language, Italian: ; ) is the capital city, capital and List of cities in Baden-Württemberg by population, largest city of the States of Germany, German state of ...
, and Wiesbaden
Wiesbaden (; ) is the capital of the German state of Hesse, and the second-largest Hessian city after Frankfurt am Main. With around 283,000 inhabitants, it is List of cities in Germany by population, Germany's 24th-largest city. Wiesbaden form ...
.
SPUIs are also found in Australia, Canada, Hong Kong, Indonesia, and Singapore.
Variants
Inverted SPUI
A rarely built variant of the SPUI is the inverted SPUI, in which the carriageway
A carriageway (British English) or roadway (North American English) is a width of road on which a vehicle is not restricted by any physical barriers or separation to move laterally. A carriageway generally consists of a number of traffic lane ...
s of the free-flowing road are separated, with left on- and offramps running between the carriageways and coming to a single at-grade intersection
An intersection or an at-grade junction is a junction where two or more roads converge, diverge, meet or cross at the same height, as opposed to an interchange, which uses bridges or tunnels to separate different roads. Major intersections ar ...
with the cross street. This can be built less expensively than a standard SPUI by allowing for shorter, simpler bridges at the interchange. However, this inverts the usual convention of placing carriageway on- and offramps on the right side of the carriageway, instead placing them on the left side, usually considered the passing lane.
Notable examples
* Interstate 290 in Oak Park, Illinois
Oak Park is a village in Cook County, Illinois, United States, adjacent to Chicago. It is the List of municipalities in Illinois, 26th-most populous municipality in Illinois, with a population of 54,318 as of the 2020 census. Oak Park was first se ...
, near Chicago
Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...
, at South Harlem Avenue () and at South Austin Boulevard ().
* Greensboro, North Carolina
Greensboro (; ) is a city in Guilford County, North Carolina, United States, and its county seat. At the 2020 United States census, 2020 census, its population was 299,035; it was estimated to be 307,381 in 2024. It is the List of municipalitie ...
, connecting West Wendover Avenue to South Holden Road ().
* Interstate 244
Interstate 244 (I-244), also known as the Martin Luther King Jr. Memorial Expressway (in honor of Martin Luther King Jr.) since 1984, the Crosstown Expressway, and the Red Fork Expressway, is a east–west Interstate Highway bypass rou ...
in Tulsa
Tulsa ( ) is the second-most-populous city in the state of Oklahoma, after Oklahoma City, and the 48th-most-populous city in the United States. The population was 413,066 as of the 2020 census. It is the principal municipality of the Tul ...
, Oklahoma
Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...
, at Sheridan Road () and at Memorial Drive ().
* U.S. Route 422 in Reading, Pennsylvania
Reading ( ; ) is a city in Berks County, Pennsylvania, United States, and its county seat. The city had a population of 95,112 at the 2020 United States census, 2020 census and is the List of municipalities in Pennsylvania, fourth-most populous ...
, at U.S. Route 222 Business ().
* State Route 18 in St. George, Utah, at Red Hills Parkway.
* Woodall Rogers Freeway (TX Spur 366), in Dallas, Texas
Dallas () is a city in the U.S. state of Texas and the most populous city in the Dallas–Fort Worth metroplex, the List of Texas metropolitan areas, most populous metropolitan area in Texas and the Metropolitan statistical area, fourth-most ...
at Riverfront Boulevard, immediately before the Margaret Hunt Hill Bridge
The Margaret Hunt Hill Bridge is a cable-stayed bridge in Dallas, Texas, that spans the Trinity River (Texas), Trinity River. The bridge is named for Margaret Hunt Hill, an heiress and philanthropist. The bridge was constructed as part of the Tr ...
().
Continuous green T (or seagull) hybrid
There is also a variant of the inverted SPUI, which can be used when a side road ends at, rather than crossing, a free-flowing road. In this variant, one carriageway of the free-flowing road is grade-separated from the side road, as with a typical inverted SPUI, while the other carriageway of the free-flowing road is at-grade with but still separated from the side road, as found in a continuous green T- (or seagull) intersection.
There is one such interchange in Pultney Township, Belmont County, Ohio, between State Route 7 (SR 7) and Interstate 470 (I-470) at . The ramps leading to and from I-470 run west of, but are not directly connected to, SR 7; these ramps form the "side road" at this interchange. The southbound carriageway of SR 7 bridges over the interchange, while its northbound carriageway remains at-grade. SR 7's left on- and offramps run between its carriageways, meeting the I-470 ramps at an at-grade intersection. The I-470 ramps proceed to a trumpet interchange
In the field of road transport, an interchange (American English) or a grade-separated junction (British English) is a road junction that uses grade separations to allow for the movement of traffic between two or more roadways or highways, usi ...
with I-470. I-470 itself bridges over both carriageways of SR 7 a short distance north of the I-470/SR 7 ramps' intersection. This design was likely chosen not for cost savings but because the northbound carriageway of SR 7 is bordered by railroad tracks, commercial properties, and the Ohio River
The Ohio River () is a river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing in a southwesterly direction from Pittsburgh, Pennsylvania, to its river mouth, mouth on the Mississippi Riv ...
and because I-470 bridges the river just east of SR 7—a more conventional interchange design was likely more difficult to achieve.
There is another such interchange in Millvale, Pennsylvania
Millvale is a borough in Allegheny County, Pennsylvania, United States, along the Allegheny River, opposite Pittsburgh. The borough is located off Pennsylvania Route 28. The population was 3,376 at the 2020 census.
Current estimates place the ...
, near Pittsburgh
Pittsburgh ( ) is a city in Allegheny County, Pennsylvania, United States, and its county seat. It is the List of municipalities in Pennsylvania#Municipalities, second-most populous city in Pennsylvania (after Philadelphia) and the List of Un ...
, at the junction between Pennsylvania Route 28
Pennsylvania Route 28 (PA 28) is a major state highway, which runs for from Anderson Street in Pittsburgh to U.S. Route 219 (US 219) in Brockway in Pennsylvania in the United States.
From Pittsburgh to Kittanning, it is a limited acc ...
(PA 28) and the 40th Street Bridge. The northbound carriageway of PA 28 passes under the interchange, with lefthand ramps meeting at the bridge (the northbound entrance ramp does not provide direct access to PA 28). The southbound carriageway of PA 28 has a continuous green T-intersection with the bridge.
A similar interchange exists in Coal Grove, Ohio, at the junction of U.S. Route 52 (US 52) with the Ben Williamson Memorial Bridge and the Simeon Willis Memorial Bridge, which cross the Ohio River
The Ohio River () is a river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing in a southwesterly direction from Pittsburgh, Pennsylvania, to its river mouth, mouth on the Mississippi Riv ...
and lead to and from Ashland, Kentucky
Ashland is a List of cities in Kentucky, home rule-class city in Boyd County, Kentucky, United States. The most populous city in Boyd County, Ashland is located upon the southern bank of the Ohio River at the state border with Ohio and near West ...
, respectively. The eastbound carriageway of US 52 passes under the interchange, with lefthand exit and entrance ramps to the bridges. The westbound carriageway of US 52, which narrows to one throughlane, has a continuous green T-intersection with the bridges. The ramps cross each other at-grade, with a 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 ...
-controlled intersection.
An interchange, like that in Millvale, Pennsylvania, formerly existed at the junction of SR 7 and SR 822 at the now-demolished Fort Steuben Bridge in Steubenville, Ohio
Steubenville ( ) is a city in Jefferson County, Ohio, United States, and its county seat. Located along the Ohio River west of Pittsburgh, it had a population of 18,161 at the 2020 United States census, 2020 census. The Weirton–Steubenville m ...
. The northbound carriageway of SR 7 passed under the bridge, with lefthand ramps meeting the bridge approach, while the southbound carriageway had a continuous green T-intersection with the bridge.
Offset SPUI
An offset SPUI is similar to a diamond interchange, however, by making two of the ramps flyovers or flyunders, all ramps are pushed to one side of the highway, where they meet the surface street at a single intersection. An example of this is the interchange between Interstate 225 and Alameda Avenue near the Town Center at Aurora shopping center in Aurora, Colorado
Aurora (, ) is a List of municipalities in Colorado#Home rule municipality, home rule city located in Arapahoe County, Colorado, Arapahoe, Adams County, Colorado, Adams, and Douglas County, Colorado, Douglas List of counties in Colorado, counti ...
, United States (at ).
Three-level SPUI
A three-level SPUI is similar to a standard SPUI but includes an additional grade separation allowing for free-flowing through traffic on the crossroad; such through traffic thus bypasses the signalized intersection. The remaining intersection, free of the crossroad's through traffic, uses a two-phase traffic signal for handling the left turns in pairs, similar to the traffic flow at an inverted SPUI.
Examples include:
* Jalan Tun Abdul Razak (Federal Route 1) in Johor Bahru
Johor Bahru, abbreviated as JB, is the capital city of the Malaysian state of Johor. It is the core city of Johor Bahru District, Malaysia's second-largest district by population and the second-largest district economy. Covering an area of ...
, Johor
Johor, also spelled Johore,'' is a States and federal territories of Malaysia, state of Malaysia in the south of the Malay Peninsula. It borders with Pahang, Malacca and Negeri Sembilan to the north. Johor has maritime borders with Singapore ...
, Malaysia
Malaysia is a country in Southeast Asia. Featuring the Tanjung Piai, southernmost point of continental Eurasia, it is a federation, federal constitutional monarchy consisting of States and federal territories of Malaysia, 13 states and thre ...
, at Jalan Lingkaran Daram (Federal Route 188). Jalan Lingkaran Daram passes over the SPUI. ().
* Central Expressway (CTE) in Singapore
Singapore, officially the Republic of Singapore, is an island country and city-state in Southeast Asia. The country's territory comprises one main island, 63 satellite islands and islets, and one outlying islet. It is about one degree ...
, at Braddell Underpass. Braddell Road passes under the SPUI. ();
* Jinxing Avenue ( Chinese: 金星大道 Pinyin
Hanyu Pinyin, or simply pinyin, officially the Chinese Phonetic Alphabet, is the most common romanization system for Standard Chinese. ''Hanyu'' () literally means 'Han Chinese, Han language'—that is, the Chinese language—while ''pinyin' ...
: Jīnxīng dàdào) in Yubei District
Yubei District (), literally meaning ''the north of Yu'' (with ''Yu'' being an abbreviation for Chongqing), is a district of Chongqing municipality, bordering Sichuan province to the north. Lianglu, which is a town administered by Yubei District, ...
, Chongqing
ChongqingPostal Romanization, Previously romanized as Chungking ();. is a direct-administered municipality in Southwestern China. Chongqing is one of the four direct-administered municipalities under the State Council of the People's Republi ...
, China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
, at Food City Avenue (Chinese: 食品城大道 Pinyin: Shípǐn chéng dàdào). This is a partial three-level SPUI in which one of the ramps from Food City Avenue to Jinxing Avenue passes under the SPUI. ().
References
External links
Michigan Department of Transportation page about SPUIs
Missouri Department of Transportation page about SPUIs
{{Road
Road interchanges
de:Anschlussstelle (Autobahn)#Raute mit einer Kreuzung