![spui-schematic](https://upload.wikimedia.org/wikipedia/commons/b/b1/Spui-schematic.svg)
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
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, using ...
. The design was created in order to help move large volumes of traffic through limited amounts of space safely and efficiently.
Description
![Taylor Street single-point urban interchange on CA-87](https://upload.wikimedia.org/wikipedia/commons/b/b8/Taylor_Street_single-point_urban_interchange_on_CA-87.jpg)
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-separated from the minor road, one crossing the other over a bridge. Approaching the ...
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 – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic.
Traffic light ...
s. Due to the space efficiency of SPUIs relative to the volume of traffic they can handle, the interchange design is being 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. A frontage road is often used to provide access to private drivew ...
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 are 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 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 passes over or under the ...
, allowing construction to take place on a limited amount of property and minimizing state use of
eminent domain
Eminent domain (United States, Philippines), land acquisition (India, Malaysia, Singapore), compulsory purchase/acquisition (Australia, New Zealand, Ireland, United Kingdom), resumption (Hong Kong, Uganda), resumption/compulsory acquisition (Austr ...
.
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
Yellowhead Trail is a expressway segment of the Yellowhead Highway (Highway 16) in northern Edmonton, Alberta, Canada. It carries a significant amount of truck traffic to and from the industrial areas of north Edmonton and serves as a key co ...
in
Edmonton
Edmonton ( ) is the capital city of the Canadian province of Alberta. Edmonton is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Alberta's central region. The city ancho ...
, 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.
Additionally, 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.
Also, 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 located in Pinellas County, Florida, United States, northwest of Tampa and St. Petersburg. To the west of Clearwater lies the Gulf of Mexico and to the southeast lies Tampa Bay. As of the 2020 census, the city had a populat ...
. It was designed by Wallace Hawkes, Director of Transportation Engineering at J. E. Greiner Company
J. E. Greiner Company was a Baltimore, Maryland-based civil engineering firm specializing in bridge design.
History
The firm was founded in 1908 by former Baltimore and Ohio Railroad bridge engineer John Edwin Greiner (February 24, 1859 – N ...
(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 recently 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. A frontage road is often used to provide access to private drivew ...
s in each direction.
Several SPUIs, built in the 1970s and later, are located on German autobahns, like the A40, A42, A44 A44 may refer to :
* A44 road (Great Britain), a road connecting Oxford, England and Aberystwyth, Wales
* A44 motorway (Germany), a road connecting Aachen at the German-Belgian border and Kassel
* A44 motorway (Netherlands), a motorway in the Nethe ...
, A46, A57, A59, and A113
A113 (sometimes A-113, A-1-13, A1-13 or A11-3) is an inside joke and Easter egg in media developed by alumni of California Institute of the Arts, referring to the classroom used by graphic design and character animation students.
History
Student ...
in Berlin
Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitue ...
. There is also a SPUI on the ''Frankenschnellweg'', the urban part of the A73, and Maximilianstraße, in Nuremberg
Nuremberg ( ; german: link=no, Nürnberg ; in the local East Franconian dialect: ''Nämberch'' ) is the second-largest city of the German state of Bavaria after its capital Munich, and its 518,370 (2019) inhabitants make it the 14th-largest ...
(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. With over 126,000 residents, it is the sixth-largest city in the state.
From the late Mid ...
, Karlsruhe
Karlsruhe ( , , ; South Franconian: ''Kallsruh'') is the third-largest city of the German state (''Land'') of Baden-Württemberg after its capital of Stuttgart and Mannheim, and the 22nd-largest city in the nation, with 308,436 inhabitants. ...
, 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.
History
* 1155 ...
, Stuttgart
Stuttgart (; Swabian: ; ) is the capital and largest city of the German state of Baden-Württemberg. It is located on the Neckar river in a fertile valley known as the ''Stuttgarter Kessel'' (Stuttgart Cauldron) and lies an hour from the ...
, and Wiesbaden
Wiesbaden () is a city in central western Germany and the capital of the state of Hesse. , it had 290,955 inhabitants, plus approximately 21,000 United States citizens (mostly associated with the United States Army). The Wiesbaden urban area ...
.
SPUIs are also found in Australia, 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) consists of 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 tra ...
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 a ...
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
A passing lane (North American English) or overtaking lane (English outside of North America) is a lane on a multi-lane highway or motorway closest to the median of the road (the central reservation). In some countries, lanes are described as bein ...
.
Notable examples
* Interstate 290 in Oak Park, Illinois
Oak Park is a village in Cook County, Illinois, adjacent to Chicago. It is the 29th-most populous municipality in Illinois with a population of 54,583 as of the 2020 U.S. Census estimate. Oak Park was first settled in 1835 and later incorporated in ...
, near Chicago
(''City in a Garden''); I Will
, image_map =
, map_caption = Interactive Map of Chicago
, coordinates =
, coordinates_footnotes =
, subdivision_type = Country
, subdivision_name ...
, at South Harlem Avenue () and at South Austin Boulevard ().
* Greensboro, North Carolina
Greensboro (; formerly Greensborough) is a city in and the county seat of Guilford County, North Carolina, United States. It is the third-most populous city in North Carolina after Charlotte and Raleigh, the 69th-most populous city in the Un ...
, 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 route ...
in Tulsa
Tulsa () is the second-largest city in the U.S. state, state of Oklahoma and List of United States cities by population, 47th-most populous city in the United States. The population was 413,066 as of the 2020 United States census, 2020 census. ...
, Oklahoma
Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...
, at Sheridan Road () and at Memorial Drive ().
* U.S. Route 422 in Reading, Pennsylvania
Reading ( ; Pennsylvania Dutch: ''Reddin'') is a city in and the county seat of Berks County, Pennsylvania, United States. The city had a population of 95,112 as of the 2020 census and is the fourth-largest city in Pennsylvania after Philade ...
, at U.S. Route 222 Business ().
* State Route 18 in St. George, Utah
St. George is a city in and the county seat of Washington County, Utah, United States. Located in southwestern Utah on the Arizona border, it is the principal city of the St. George Metropolitan Statistical Area (MSA). The city lies in the northe ...
, at Red Hills Parkway.
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
Pultney Township is one of the sixteen townships of Belmont County, Ohio, United States. The 2020 census found 8,163 people in the township.
Geography
Located in the eastern part of the county along the Ohio River, it borders the following town ...
, 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, using ...
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 long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...
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 3,744 at the 2010 census.
Geography
Millvale is locate ...
, near Pittsburgh
Pittsburgh ( ) is a city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania, United States, and the county seat of Allegheny County, Pennsylvania, Allegheny County. It is the most populous city in both Allegheny County and Wester ...
, 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. From Pittsburgh to Kittanning it is a limited access expressway named the ...
(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
Coal Grove is a village in Lawrence County, Ohio, United States, along the Ohio River. The population was 2,165 at the 2010 census. It borders the city of Ironton and lies across the Ohio River from Ashland, Kentucky. It is linked to Ashland by ...
, at the junction of U.S. Route 52 (US 52) with the Ben Williamson Memorial Bridge
The Ben Williamson Memorial Bridge, known locally as the Old Ben, is a cantilever bridge that connects Coal Grove, Ohio to Ashland, Kentucky, crossing the Ohio River. Completed in 1932, it is named for Senator Ben M. Williamson. The bridge was f ...
and the Simeon Willis Memorial Bridge
Simeon Willis Memorial Bridge is a bridge crossing the Ohio River connecting US 23 and (US 60) in Ashland, Kentucky to US 52 in Coal Grove, Ohio.
Opened in 1985, the bridge is named for Kentucky Governor Simeon S. Willis. The bridge was origin ...
, which cross the Ohio River
The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...
and lead to and from Ashland, Kentucky
Ashland is a home rule-class city in Boyd County, Kentucky, United States. The largest city in Boyd County, Ashland is located upon a southern bank of the Ohio River at the state border with Ohio and near West Virginia. The population was 21,6 ...
, 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 At-grade may refer to:
* At-grade intersection, a crossing between roads on the same level
* Road junction
*Level crossing, where a road or path crosses a railway on the same level
* Diamond crossing, where two railway tracks cross
* At-grade railwa ...
, with a traffic light
Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
-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
The Fort Steuben Bridge, originally the Weirton-Steubenville Bridge, was a suspension bridge which spanned the Ohio River from Steubenville, Ohio to Weirton, West Virginia and carried U.S. Route 22 and then Ohio State Route 822 during its exis ...
in Steubenville, Ohio
Steubenville is a city in and the county seat of Jefferson County, Ohio, United States. Located along the Ohio River 33 miles west of Pittsburgh, it had a population of 18,161 at the 2020 census. The city's name is derived from Fort Steuben, a 1 ...
. 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
Interstate 225 (I-225) is an auxiliary Interstate Highway in the U.S. state of Colorado. The freeway is a connector spur route of I-25 that acts as an eastern bypass in the Denver metropolitan area and serves Aurora. It also provides direct ...
and Alameda Avenue near the Town Center at Aurora
The Town Center at Aurora (formerly known as Aurora Mall) is an enclosed, two-level regional shopping center located in Aurora, Colorado, and covers a leasable area over 1 million square feet. It lies at the center of the commercial and retail d ...
shopping center in Aurora, Colorado
Aurora (, ) is a List of municipalities in Colorado#Home rule municipality, home rule municipality located in Arapahoe County, Colorado, Arapahoe, Adams County, Colorado, Adams, and Douglas County, Colorado, Douglas List of counties in Colorado, ...
, 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 (), colloquially referred to as JB, is the capital city of the state of Johor, Malaysia. It is located at the southern end of Peninsular Malaysia,along the north bank of the Straits of Johor, opposite of the city-state Singapore. T ...
, Johor
Johor (; ), also spelled as Johore, is a States and federal territories of Malaysia, state of Malaysia in the south of the Malay Peninsula. Johor has land borders with the Malaysian states of Pahang to the north and Malacca and Negeri Sembilan ...
, Malaysia
Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
, 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 a sovereign island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, borde ...
, at Braddell Underpass. Braddell Road passes under the SPUI. ();
* Jinxing Avenue (Chinese
Chinese can refer to:
* Something related to China
* Chinese people, people of Chinese nationality, citizenship, and/or ethnicity
**''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation
** List of ethnic groups in China, people of va ...
: 金星大道 Pinyin
Hanyu Pinyin (), often shortened to just pinyin, is the official romanization system for Standard Mandarin Chinese in China, and to some extent, in Singapore and Malaysia. It is often used to teach Mandarin, normally written in Chinese for ...
: 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
Chongqing ( or ; ; Sichuanese dialects, Sichuanese pronunciation: , Standard Mandarin pronunciation: ), Postal Romanization, alternately romanized as Chungking (), is a Direct-administered municipalities of China, municipality in Southwes ...
, China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
, 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
{{Road
Road interchanges
de:Anschlussstelle (Autobahn)#Raute mit einer Kreuzung