Single-point urban interchange
||The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject. (December 2013)|
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 safely and efficiently.
- 1 Overview
- 2 Advantages
- 3 Disadvantages
- 4 Use in North America
- 4.1 Canada
- 4.2 United States of America
- 4.2.1 Alabama
- 4.2.2 Alaska
- 4.2.3 Arizona
- 4.2.4 California
- 4.2.5 Colorado
- 4.2.6 Connecticut
- 4.2.7 Florida
- 4.2.8 Georgia
- 4.2.9 Idaho
- 4.2.10 Indiana
- 4.2.11 Kentucky
- 4.2.12 Maryland
- 4.2.13 Michigan
- 4.2.14 Minnesota
- 4.2.15 New Hampshire
- 4.2.16 New York
- 4.2.17 North Carolina
- 4.2.18 Ohio
- 4.2.19 Oklahoma
- 4.2.20 South Dakota
- 4.2.21 Tennessee
- 4.2.22 Utah
- 4.2.23 Virginia
- 5 Inverted SPUI
- 6 See also
- 7 References
- 8 External links
A single point urban interchange is similar in form to a diamond interchange, 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 signals. 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.
The first SPUI opened on February 25, 1974 along US 19 (SR 55), which goes over SR 60 east of Clearwater, Florida. It was designed by Wallace Hawkes, Director of Transportation Engineering at J.E. Greiner, Inc. (now URS Corporation), who has been called the "granddaddy of the urban interchange".
Sometimes a SPUI will allow traffic to proceed straight through from the off-ramp to the on-ramp; this usually happens when the ramps connect with frontage roads. Since most through traffic travels over or under the intersection, the SPUI is still much more efficient than a surface intersection.
The most commonly cited advantages of single point urban interchanges 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, allowing construction to take place on a limited amount of property and minimizing state use of eminent domain.
Finally, single point urban interchanges 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.
The major disadvantage of single point urban interchanges 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 off-ramps. However, this disadvantage poses less of a problem in cases where the arterial, or non-freeway road already requires a very wide bridge. The intersection of 97 Street, having seven through lanes, with Yellowhead Trail in Edmonton, 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 right-hand side (or left-hand side in countries that drive on the left).
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.
Use in North America
There is a SPUI at the intersection of MacLeod Trail and Glenmore Trail in the City of Calgary
In Ontario there are two SPUIs. One is located on the Airport Parkway (Ottawa Road 79) in Ottawa at the Hunt Club Road (Ottawa Road 32) interchange. The other is on Highway 406 at the Fourth Avenue (Niagara Regional Road 77) interchange in St. Catharines.
United States of America
In Huntsville there are four SPUIs on Memorial Parkway SW.
In Fairbanks there are two SPUIs on the Johansen Expressway, one at the junction with College Road and the other at the junction with Peger Road. A modified SPUI exists at the intersection of the George Parks Highway, Seward Meridian Parkway and Fireweed Road in Wasilla.
On Interstate 19 in Tucson there is one SPUI at the West Valencia Road interchange. On Interstate 10 in Phoenix there are two SPUIs; one at the North 7th Street interchange and one at the North 7th Avenue interchange. On Interstate 17 in Phoenix there are a total of five SPUIs at the following cross roads; West Dunlap Avenue, West Northern Avenue, West Glendale Avenue, West Bethany Home Road and West Camelback Road. There are several SPUIs on Arizona State Route 51 in Phoenix at the following cross roads with the freeway; East McDowell Road, East Thomas Road, East Indian School Road, a modified SPUI at East Bethany Home Road, East Glendale Avenue, East Shea Boulevard, East Cactus Road, East Greenway Road, East Bell Road and East Union Hills Drive. On Arizona State Route 202 in Tempe there is a single SPUI with North Scottsdale Road and in Phoenix there are three SPUIs at these cross roads; North 44th Street, North 32nd Street and North 24th Street. In the short length of Arizona State Route 143 there are two SPUIs; one at the junction with East Washington Street and the other at the junction with West University Drive. On Arizona State Route 101 there is an extensive number of SPUIs, starting at the junction with State Route 202 the SPUI interchange list goes as follows; East Guadalupe Road, North Pima Road, East Shea Boulevard, East Cactus Road, East Raintree Drive, North Frank Lloyd Wright Boulevard, North Tatum Boulevard, North Cave Creek Road, West Bell Road, West Glendale Avenue and West Camelback Road.
A SPUI exists at the intersection of SH-470 and SH-8 (Morrison Road) in Morrison. Another exists at the intersection of US-85 (Santa Fe Drive) and Evans Avenue in Denver. This SPUI was necessitated by a multi-track rail corridor directly to the east of Santa Fe Drive.
The first SPUI in the U.S. was built near Clearwater in 1974. It is located where US19 crosses SR60. There are several others in the state, including one at the eastern terminus of the Beachline Expressway at Florida State Road 401.
Currently a SPUI is in use at Sugarloaf Parkway and New Hope Road near Lawrenceville, GA on the Sugarloaf Parkway extension.
There is a SPUI at the junction of I-84 and S. Vista Ave in Boise.
There is a SPUI at the junction of I-75 and SH92 at Williamsburg in Southern Kentucky. There are nine total in Kentucky with one under construction.
There is a SPUI at the junction of I-70 and MD-85/East St. in Frederick.
There is a SPUI at the junction of I-270 and Falls Rd. in Rockville.
There is a SPUI at the junction of MD-100 and MD-170/Telegraph Rd. in Severn
There is a SPUI at the junction of MD-29 and Randolph Rd./Cherry Hill Rd.
SPUIs are in use at the Beck Road and Wixom Road exits of I-96 in Novi, MI, the Telegraph Road exit of I-94 in Taylor, MI east of the Detroit Metropolitan Wayne County Airport, and the M-59 exit of US-23 in Hartland, MI.
The first SPUI in New Hampshire was constructed at the interchange between NH 101 and NH 125 in Epping, NH.
A SPUI replaced the old-fashioned intersection of NY State Route 7 (Troy-Schenectady Rd) & I-87 Exit 6 in Latham, NY. If you would like to see it via Google Maps the URL is: https://www.google.com/maps?q=42.753126,-73.76897 The SPUI has its own website at: http://alloveralbany.com/archive/2008/09/17/the-latham-spui-now-has-its-own-website.
The first SPUI in Oklahoma was constructed at I-40 and Morgan Road on the west side of Oklahoma City. A second SPUI is currently under construction at the junction of I-35 and W. Main St. in Norman and is expected to open in mid-2014.
Several SPUIs serve the freeway system around Sioux Falls. Exit 6 of I-229 on SD-42 (10th Street)/Downtown was the first in the city. The newest is at exit 399 of I-90 on SD-115 (Cliff Avenue)/Renner. I-29 contains four SPUIs (from north to south): exit 82 (Benson Road), exit 80 (Madison Street/Ellis), exit 79 (SD-42 (12th Street)/Downtown), and exit 73 (Tea/101st Street/future SD-100).
On I-65 at mile marker 67 in Franklin, there is a SPUI at the McEwen Drive exit. Briley Parkway(TN-155) intersection with McGavock Pike at Oprylnd Hotel in Nashville
Briley Parkway(TN-155) intersection with McGavock Pike at Oprylnd Hotel in Nashville
Utah uses several SPUIs on I-15 along the Wasatch Front.
VA 7 at Loudoun County Parkway.
A rarely built variant of the SPUI is the inverted SPUI, in which the carriageways of the free-flowing road are separated, with left on- and off-ramps running between the carriageways and coming to a single at-grade intersection with the cross street. This can be built less expensively than a standard SPUI by allowing for shorter, simpler bridges at the interchange. An inverted SPUI in Greensboro, North Carolina connects West Wendover Avenue to South Holden Road at .
A variation on an inverted SPUI forms part of a larger, hybrid interchange in Pultney Township, Belmont County, Ohio, between Bellaire and Bridgeport. The inverted SPUI connects north–south State Route 7 (the free-flowing road) with the ramps to and from east–west Interstate 470 (with the ramps forming the cross street) at . As the I-470 ramps only run west of SR 7, then curve north to I-470 (ending at a trumpet interchange), only the southbound carriageway of SR 7 bridges over them, while SR 7's northbound carriageway remains at-grade. SR 7's left on- and off-ramps run between its carriageways, meeting I-470's ramps at an at-grade intersection. I-470 itself bridges over both carriageways of SR 7 a short distance north of the 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, and because I-470 bridges the river just east of SR 7 – a more conventional interchange design was likely more difficult to achieve.
- Anonymous (July 1989). "Urban interchange moves more traffic in same space; a design new to California improves congested diamond interchanges without taking more high-priced real estate". Highway & Heavy Construction 132 (8): 52–53. ISSN 0362-0506.
- St. Louis District. "Single Point Urban Interchanges". Missouri Department of Transportation. Retrieved July 15, 2012.
- "Single-point Urban Interchange (SPUI)". Kurumi.com. Retrieved April 9, 2008.
- Bonneson, James A. (January 1993). "Bridge Size and Clearance Time of Single Point Urban Interchange". Journal of Transportation Engineering (American Society of Civil Engineers) 119 (1): 77–93. doi:10.1061/(ASCE)0733-947X(1993)119:1(77). ISSN 0733-947X.
- St. Louis District. "Single Point Urban Interchange Frequently Asked Questions". Missouri Department of Transportation. Retrieved July 15, 2012.
- Bared, Joe; Powell, Alvin; Kaisar, Evangelos; Jagannathan, Ramanujan (May 2005). "Crash Comparison of Single Point and Tight Diamond Interchanges". Journal of Transportation Engineering (American Society of Civil Engineers) 131 (5): 379–381. doi:10.1061/(ASCE)0733-947X(2005)131:5(379). ISSN 0733-947X.
- Qureshi, Mohammad; Sugathan, Navin; Lasod, Rohit; Spring, Gary (September 2004). "Design of Single Point Urban Interchanges, Research Investigation 02-015" (PDF). Missouri Department of Transportation Research, Development, and Technology, University of Missouri-Rolla. Retrieved February 10, 2010.
- "Idaho’s First SPUI – I-84 Vista Interchange". Stanley Consultants. Retrieved July 31, 2013.
- Michigan Department of Transportation. "US-23/M-59 opens; SPUI introduced in Livingston County". Michigan Department of Transportation. Retrieved September 26, 2013.
- Jonathan Reid, P.E. (July 2004). "Unconventional arterial intersection design, management and operations strategies" (PDF). Parsons Brinckerhoff. Retrieved 2012-09-09.
- Michigan Department of Transportation page about SPUIs
- Missouri Department of Transportation page about SPUIs
- Page about SPUIs at kurumi.com