Editing Roundabout (section)

== Operation and design ==
{{more footnotes needed|section|date=December 2013}}
[[File:Elovainio shopping center roundabout - panoramio.jpg|thumb|A roundabout next to the Elovainio shopping centre in [[Ylöjärvi]], Finland]]
[[File:Rotatoria incorcio di Corso Italia, Via Roma e Via P.Micca nel centro di Legnano. 2015-02-22.jpg|thumb|An oval roundabout in [[Legnano]], Italy]]

The fundamental principle of modern roundabouts is that entering drivers give way to traffic within the roundabout without the need for traffic signals. Conversely, older traffic circles typically require circling drivers to give way to entering traffic. Roundabouts may also have an interior lane.<ref>{{cite book|url=http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa10006/|archive-url=https://web.archive.org/web/20100417120518/http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa10006/|url-status=dead|archive-date=17 April 2010|title=Intersection Safety Roundabouts – Safety – Federal Highway Administration|date=February 2010 |access-date=17 October 2018}}</ref> Generally, exiting directly from an inner lane of a multi-lane roundabout is permitted, given that the intersecting road has as many lanes as the roundabout. By contrast, exiting from an inner lane of an older traffic circle is usually not permitted and traffic must first move into the outside lane.

Vehicles circulate around the central island in one direction at speeds of {{convert|25|-|40|km/h|abbr=on|round=5|mph}}. In [[left-hand traffic]] countries they circulate [[clockwise]] (looking from above); in right-hand traffic, anticlockwise.

Multi-lane roundabouts are typically less than {{convert|75|m|round=10}} in diameter;<ref>{{cite web|url=http://www.ksdot.org/burtrafficeng/Roundabouts/Roundabout_Guide/Chapter_6_Geometric_Design.pdf |title=Kansas Roundabout Guide: A Supplement to FHWA's Roundabouts: An Informational Guide| author=Kittleson & Associates |work=Kansas Department of Transportation |access-date=26 August 2009}}</ref> older traffic circles and [[roundabout interchange]]s may be considerably larger. Roundabouts are roughly the same size as signalled intersections of the same capacity.

Design criteria include:
* Right-of-way: Whether entering or circling vehicles have the right of way. The [[New Jersey]] Driver's Manual recommends that, in the absence of flow control signs, traffic yields based on "the circle's historically established traffic flow pattern",<ref>{{cite web|url=https://www.state.nj.us/mvc/pdf/license/drivermanual.pdf |title=Driver manual |access-date=13 August 2021}}</ref> and there are no set rules. In [[New England]],<ref>{{cite web|url=http://www.mass.gov/rmv/dmanual/index.htm |title=Sharing the Road: A User's Manual for Public Ways |author=Commonwealth of Massachusetts, Registry of Motor Vehicles |access-date=13 May 2009}}</ref> [[Washington, D.C.]], and [[New York State]],<ref>{{cite web|url=http://safeny.com/rowa-vt.htm#1145|archive-url=https://web.archive.org/web/20110703061007/http://safeny.com/rowa-vt.htm#1145|url-status=dead|archive-date=3 July 2011|title=Vehicle & Traffic Law – Right of Way|date=3 July 2011|access-date=17 October 2018}}</ref> entering traffic yields, as is the norm in virtually all countries outside of the U.S.
* Angle of entry: Angles range from glancing ([[tangent]]ial) that allow full-speed entry to 90 degree angles ([[perpendicular]]).<ref name="ModernRoundabouts">{{cite web|url=https://www.fhwa.dot.gov/publications/research/safety/00067/index.cfm|title=Index – Roundabout: An Informational Guide, June 2000 – FHWA-RD-00-067|website=Fhwa.dot.gov|access-date=17 October 2018}}</ref> Deflection is required to avoid vehicles entering at excessive speeds.<ref>TSM https://en.wikisource.org/wiki/Traffic_Signs_Manual/Chapter_5/2009/8</ref>
* Traffic speed: High entry speeds (over {{convert|30|mph|km/h|abbr=on|disp=or}}) require circulating vehicles to yield, often stopping, which lowers capacity and increases crash rates compared to modern roundabouts.<ref>{{cite web|url=http://findarticles.com/p/articles/mi_qa3734/is_200703/ai_n18755716/pg_1 |title=A Comparative Evaluation of the Safety Performance of Roundabouts and Traditional Intersection Controls |author=Shashi S. Nambisan, Venu Parimi |date=March 2007 |work=Institute of Transportation Engineers |access-date=27 November 2007}}</ref>
* Lane changes: Allowed or not
* Diameter: The greater the traffic, the larger the circle.<ref name="ModernRoundabouts" />
* Island function: Parking, parks, fountains, etc.<ref name="ModernRoundabouts" />

=== Islands ===
[[File:LUMC-rotonde.JPG|thumb|Roundabout at [[Leiden University Medical Center]] in the Netherlands, with modern art animals on the central island, and an apron that can be used by large trucks.]]

Modern roundabouts feature a central island and sometimes pedestrian islands at each entry or exit often for decoration.

Denmark has begun widespread adoption of particular high islands, or if not possible, obstacles such as hedges or a ring of trees in larger examples. This is done to further increase the safety benefits of roundabouts, as the obstacles have been found to discomfort drivers more so than the roundabout itself compared to conventional intersections, thus initiating further observation and care taking of the driver. In Denmark, it was found to decrease accidents in roundabouts by 27% to 84% depending on height and type. In studies, heights of 0-0.9, 1-1.9 and 2+ metres were evaluated. It was found that for all heights, especially accidents leading to human injuries were reduced the most, by -47% to -84% for the aforementioned heights.<ref>{{Cite journal|last=Underlien Jensen|first=Søren|date=November 2012|title=Rundkørsler og trafiksikkerhed|url=https://www.trafitec.dk/sites/default/files/publications/rundk%20og%20trafiksikkerhed.pdf|journal=Trafik & Veje|language=Danish|pages=26–29}}</ref> The level of irritation to drivers is not to be understated, as it is the crucial point of the design: to force drivers to pay attention to the sides of the driving direction. This leads to drivers complaining about these designs, as Denmark in most regards embraces designing road infrastructure, such that the wanted driving behaviour leads to comfort i.e., lane width corresponding to speed limit and obstacles encouraging slowdown near points of safety concern such as schools. Such is the controversy for drivers that seasoned driving teachers complain about this discomfort a decade after its safety is proven and adoption widespread.<ref>{{Cite web|last1=sep 2020|first1=Clock 20|last2=Journalist|first2=kl 09:01 Bemærk: Artiklen er mere end 30 dage gammel Sebastian Myrup Hansen|title=Renovering af omdiskuteret rundkørsel er i gang - ikke godt nok mener kørelærer|url=https://www.tv2lorry.dk/solroed/renovering-af-omdiskuteret-rundkoersel-er-i-gang-ikke-godt-nok-mener-koerelaerer|access-date=27 January 2022|website=TV 2 Lorry|language=da}}</ref>

==== Central ====
[[File:La fontaine des trois Grâces, 1860.jpg|thumb|A fountain dominates this roundabout in [[Aix-en-Provence]], France.]]

The central island may be surrounded by a [[truck apron]] that is high enough to discourage drivers from crossing over it, but low enough to allow wide or long vehicles to navigate the roundabout. The island may provide a visual barrier, to alert approaching drivers to the presence of the roundabout, and to encourage drivers to focus on the traffic in the path of the circle. A visual barrier significantly reduces the accident rate.<ref>{{cite web |last1=Hansen |first1=Winnie |title=Spørg Fagfolket: Hvorfor skal øen i midten af rundkørslen være så høj? |url=https://ing.dk/artikel/spoerg-fagfolket-hvorfor-skal-oeen-midten-rundkoerslen-vaere-saa-hoej-225722 |website=[[Ingeniøren]] |publisher=[[Vejdirektoratet]] |language=da |date=2 June 2019 |quote=analysis of 332 roundabouts. It was very clear that if the height in the middle of the roundabout was over two meters, then it was much safer than other designs. The accident rate was significantly lower in the high roundabouts}}</ref> Otherwise, vehicles anywhere in or near the circle can cause those <!--inexperienced-->entering to stop and wait for them to pass, even if they are opposite, which unnecessarily reduces traffic flow. The barrier may be a landscaped mound, a raised wall, a tree or tall shrubs. Road signage or flagpoles may be erected at the top of a landscaped mound.

Some communities use the island for monuments, the display of large public art or for a fountain. Pedestrians may be prohibited from crossing the circling lane(s). Access to the central island requires an underpass or overpass for safety.

===== Art installations =====
[[File:Guadalajara, Jalisco, Mexico (2021) - 050.jpg|thumb|The [[Statue of Minerva, Guadalajara|Minerva Roundabout]] in [[Guadalajara]], Mexico]]
Roundabouts have attracted art installations around the world:
* [[Bend, Oregon]] (United States); Bend's roundabout sculptures were honoured by [[Americans for the Arts]] as among the 37 most innovative approaches to Public Art in the country.<ref>{{cite web|title=Art In Public Places, Bend, Oregon|url= http://artinpublicplaces.org/history.php |publisher=Art in Public Places|access-date=2 November 2013|archive-url= https://web.archive.org/web/20080509071110/http://artinpublicplaces.org/history.php |archive-date=9 May 2008|url-status=dead}}</ref><ref>{{cite web|title=Pillar of art|url=http://artinpublicplaces.org/files/VisitBend-RndAbtmap.pdf |publisher=Art in Public Places|access-date=2 November 2013|archive-url= https://web.archive.org/web/20131103202747/http://artinpublicplaces.org/files/VisitBend-RndAbtmap.pdf |archive-date=3 November 2013|url-status=dead}}</ref>
* [[Fuerteventura]], Canary Islands (Spain); Local government displayed sculptures at several roundabouts.<ref>{{cite web|title=Fuerteventura, art on the roads: roundabouts as galleries|date= 2 July 2012 |url= http://robertoalborghetti.wordpress.com/2012/07/02/art-on-the-roads-roundabouts-as-galleries-my-days-in-fuerteventura-5/ |publisher=Roberto Alborghetti|access-date=2 November 2013}}</ref>
* Many countries in Europe (France first,<ref>{{google maps|url=https://www.panoramio.com/map/?group=13339#lt=47.334499&ln=2.209236&z=11&k=0&a=1&tab=6&pl=all|title=Photographs of French roundabouts}}</ref> but also Germany,<ref name="North_Europe">{{google maps|url=https://www.panoramio.com/map/?group=13339#lt=50.912865&ln=10.075447&z=11&k=0&a=1&tab=6&pl=all |title=Roundabout photographs from The Netherlands, Belgium, Germany and Austria}}</ref> Austria,<ref name="North_Europe"/> Italy,<ref>{{google maps|url= https://www.panoramio.com/map/?group=13339#lt=42.710044&ln=11.261970&z=11&k=0&a=1&tab=6&pl=all |title=Roundabout photographs from Italy}}</ref> Spain,<ref>{{google maps|url= https://www.panoramio.com/map/?group=13339#lt=39.938544&ln=-3.239983&z=11&k=0&a=1&tab=6&pl=all |title=Roundabout photographs from Spain}}</ref> and others<ref name="North_Europe"/>) show the widespread use of roundabouts as art installations.<ref name="Panoramio_Roundabouts">{{cite web|title=Unusual road roundabouts: artistic, and otherwise. A collection of more than 2000 photographs, by almost 200 amateur photographers, from all over the world|url=https://www.panoramio.com/group/roundabouts|work=Panoramio: Roundabouts|publisher=www.panoramio.com|access-date=2 November 2013|archive-url=https://web.archive.org/web/20131103061756/http://www.panoramio.com/group/roundabouts|archive-date=3 November 2013|url-status=dead}}</ref><ref>{{cite news|title=Roundabout / Kreisverkehr – streets with a roundabout / Straßen mit einem Kreisverkehr|newspaper=Flickr |url=https://www.flickr.com/groups/350203@N21/|publisher=www.flickr.com|access-date=2 November 2013|language=en, de}}</ref>
* An inventory of roundabouts in France, made by Marc Lescuyer, listed 3,328 roundabouts with artistic decor early in 2010.<ref name="Panoramio_Roundabouts"/><ref>{{cite web|title=Inventory of French roundabouts|url= http://www.marclescuyer.fr/textesrp/pagetype.htm |publisher=Marc Lescuyer|access-date=1 January 2010|language=fr|url-status=dead|archive-url= https://web.archive.org/web/20081111032348/http://www.marclescuyer.fr/textesrp/pagetype.htm |archive-date=11 November 2008}}</ref>
* The [[Statue of Minerva, Guadalajara|Minerva Roundabout]] in [[Guadalajara]], Mexico, is one of the city's most famous monuments. It features the goddess [[Minerva]] standing on a pedestal, surrounded by a large fountain, with an inscription saying "Justice, wisdom and strength guard this loyal city".
* Several famous monuments in Europe, such as the [[Puerta de Alcalá|Gate of Alcalá]] in [[Madrid]], Spain or the [[Arc du Triomphe]] in [[Paris]], France, have been isolated from street traffic by means of a roundabout.
* The [[Garces Memorial Circle]] in [[Bakersfield, California]] contains a statue to Father [[Francisco Garces]].
* In the [[Philippines]], the town of [[Ipil, Zamboanga Sibugay]] has an Obelisk containing art and the [[Baybayin]] script.

==== Pedestrian ====
[[File:View2FromPearlTower.jpg|thumb|This roundabout in [[Shanghai]], China, has a pedestrian bridge in the form of another, raised roundabout.]]

For larger roundabouts, pedestrian islands at each entry/exit encourage drivers to slow and prepare to enter the circle. They also provide a refuge where pedestrians may pause mid-crossing.
Vehicles or bicycles entering or exiting the roundabout must yield to all traffic including pedestrians.<ref>{{Cite web|url=https://www.dmv.ca.gov/portal/handbook/california-driver-handbook/laws-and-rules-of-the-road/|title=Section 7: Laws and Rules of the Road|website=California DMV}}</ref>

=== Pedestrian crossing ===
[[Pedestrian crossing]]s at each entry/exit may be located at least one full car length outside the circle. The extra space allows pedestrians to cross behind vehicles waiting to enter the circle, and to allow exiting vehicles to stop for pedestrians without obstruction. Each pedestrian crossing may traverse a [[pedestrian island]] for protection that also forces drivers to slow and begin to change direction, encouraging slower, safer speeds. On the island, the pedestrian crossing may become diagonal, to direct the gaze of those crossing into exiting traffic.

=== Bicycles ===
Physically separated bikeways best protect cyclists.<ref name="swov-roundabouts">{{Cite web|url=https://swov.nl/en/facts-figures|title=Facts & figures|website=swov.nl}}</ref><ref name="modern" /><ref>{{Cite web|url=https://mutcd.fhwa.dot.gov/HTM/2003/part3/part3b2.htm|title=FHWA - MUTCD - 2003 Edition Chapter 3B2|website=[[Federal Highway Administration|Federal Highway Administration (FHWA)]]}}</ref> Less optimally, terminating cycle lanes well before roundabout entrances requires cyclists to merge into the stream of motor traffic, but keeps cyclists in full view of drivers, at some cost in motor vehicle speed. Cyclists may also be permitted to use pedestrian crossings. 

Traditional cycle lanes increase vehicle–bicycle collisions. When exiting, a motorist must look ahead to avoid colliding with another vehicle or with pedestrians on a pedestrian crossing. As the intersection curves away from the exit, the path of an exiting vehicle is relatively straight, and so the motorist may often not slow substantially. To give way to a cyclist on the outside requires the exiting motorist to look toward the rear, to the perimeter. Other vehicles can obstruct the driver's view in this direction, complicating the motorist's task. The more frequent requirements for motorists to slow or stop reduce traffic flow. A 1992 study<ref>R. Schnüll, J. Lange, I. Fabian, M. Kölle, F. Schütte, D. Alrutz, H.W. Fechtel, J. Stellmacher-Hein, T. Brückner, H. Meyhöfer: ''Sicherung von Radfahrern an städtischen Knotenpunkten'' [''Safeguarding bicyclists in Urban Intersections''], Bericht der Bundesanstalt für Straßenwesen zum Forschungsprojekt 8952, 1992</ref> found that the risk to cyclists is high in all such intersections, but much higher when the junction has a marked bicycle lane or sidepath around its perimeter.<ref>[http://bernd.sluka.de/Radfahren/Vortragsfolien.html Vortragsfolien Radverkehr] Scroll to the section labelled "''Kreisverkehr''". A translation of the text reads: Graphic from ''Sicherung von Radfahrern an städtischen Knotenpunkten'' [''Safeguarding cyclists in Urban Intersections''], (BASt, 1992). Accident numbers in large circular junctions with different bicycle facilities show: 1. Why there should be no pathways or bike lanes at these junctions; 2. Even when cyclists use the roadway, their risk is relatively high at these junctions.</ref><ref>Maycock, G., and Hall, R. D. (1984). "Accidents at 4-Arm Roundabouts." TRRL1120, Transport and Road Research Laboratory (TRRL), Crowthorne, England.</ref> Cycle lanes were installed at Museum Road, [[Portsmouth]], but were replaced by a narrowed [[carriageway]] to encourage lane sharing.

The roundabout at the [[Arizona State Route 202#Exit list|Brown Road and Loop 202]] interchange in [[Mesa, Arizona]], adopts a U.S.-recommended design.<ref name="adot">{{Cite web|url=https://azdot.gov/about/transportation-safety/roundabouts|title=Roundabouts &#124; ADOT|website=azdot.gov}}</ref> On-street road markings direct cyclists to enter the pavement at the end of the bike lane. Cyclists who choose to travel on the wide pavement, cross roundabout arms perpendicularly, well outside the circle. A pedestrian island allows pedestrians and cyclists to cross one lane at a time.

[[Dutch roundabout|Protected roundabouts]] (or Dutch roundabout) were developed in the [[Netherlands]], with cyclists separated from vehicles using dedicated lanes.<ref name=":0">{{Cite book |url=https://www.worldcat.org/oclc/972096448 |title=Design manual for bicycle traffic |date=2016 |others=Rik de Groot, vervoer en infrastructuur CROW kenniscentrum voor verkeer |isbn=978-90-6628-659-7 |location=Ede, The Netherlands |pages=147–148 |oclc=972096448}}</ref> As cyclists will conflict with motorists at the exit arms of the motorised roundabout, priority must be established. In the Netherlands, cyclists will normally be given priority to [[Bicycle-friendly|promote cycling]] over driving.<ref name=":0" /> As well as their use in the Netherlands and Denmark, these designs have been subsequently built in the United Kingdom and Ireland.<ref>{{Cite web |date=7 August 2020 |title=UK's first Dutch-style roundabout welcomed by road safety campaigners - Highways Industry |url=https://www.highwaysindustry.com/uks-first-dutch-style-roundabout-welcomed-by-road-safety-campaigners/ |access-date=29 July 2024 |website=Highways Industry |language=en-US}}</ref><ref>{{Cite web |date=29 May 2023 |title=Ireland's first Dutch-style roundabout opened in Dublin 15 - |url=https://irishcycle.com/2023/05/29/irelands-first-dutch-style-roundabout-opened-in-dublin-15/ |access-date=29 July 2024 |website=IrishCycle.com |language=en-GB}}</ref>

<gallery widths="200" heights="200" class="center">
File:Okay to enter sidewalk.jpg|alt=Pavement markings indicate sidewalk riding is legal.|Road markings invite cyclists to enter the pavement on approach to roundabout in [[Mesa, Arizona]]. Cyclists are still permitted to use the roundabout like any other vehicle.
File:Bicyclist in roundabout.jpg|alt=Cyclist rides through the main lane of roundabout|Cyclists can choose to ride on the pavement on far right, or in the main lanes of this roundabout in Mesa, Arizona.
File:Protected roundabout 3D.png|3D view of a [[Protected intersection|protected roundabout]], as commonly used in the Netherlands
</gallery>

=== Capacity and delays ===
[[File:ChivertonCrossRoundaboutA30Cornwall.jpg|thumb|Traffic approaching Chiverton Cross roundabout in Cornwall, UK]]

The capacity of a roundabout varies based on entry angle, lane width, and the number of entry and circulating lanes. As with other types of junctions, operational performance depends heavily on the flow volumes from various approaches. A single-lane roundabout can handle approximately 20,000–26,000 vehicles per day, while a two-lane design supports 40,000 to 50,000.<ref name="modern">{{cite web|title=Modern Roundabouts, an Informational Guide|url=https://www.fhwa.dot.gov/publications/research/safety/00068/|website=Federal Highway Administration Research and Technology|access-date=15 September 2015}}</ref>

Under many traffic conditions, a roundabout operates with less delay than signalised or [[all-way stop]] approaches. Roundabouts do not stop all entering vehicles, reducing both individual and queuing delays. Throughput further improves because drivers proceed when traffic is clear without waiting for a signal to change.

Roundabouts can increase delays in locations where traffic would otherwise often not be required to stop. For example, at the junction of a high-volume and a low-volume road, traffic on the busier road would stop only when cross traffic was present, otherwise not having to slow for the roundabout. When the volumes on the roadways are relatively equal, a roundabout can reduce delays, because half of the time a full stop would be required. Dedicated left turn signals (in countries where traffic drives on the right) further reduce throughput.

Roundabouts can reduce delays for pedestrians compared to traffic signals, because pedestrians are able to cross during any safe gap rather than waiting for a signal. During peak flows when large gaps are infrequent, the slower speed of traffic entering and exiting can still allow crossing, despite the smaller gaps.

Studies of roundabouts that replaced stop signs and/or traffic signals found that vehicle delays were reduced 13–89 percent and the proportion of vehicles that stopped was reduced 14–56 percent. Delays on major approaches increased as vehicles slowed to enter the roundabouts.<ref name="iihs"/>

Roundabouts have been found to reduce [[carbon monoxide]] emissions by 15–45 percent, [[nitrous oxide]] emissions by 21–44 percent, [[carbon dioxide]] emissions by 23–37 percent and [[hydrocarbon]] emissions by 0–42 percent. Fuel consumption was reduced by an estimated 23–34 percent.<ref name=iihs/>

==== Capacity modelling ====
Many countries have researched roundabout capacity. The software can help calculate capacity, delay and queues. Packages include [[ARCADY]], Rodel, Highway Capacity Software and [[Sidra Intersection]]. ARCADY and Rodel are based on the Transport Research Laboratory mathematical model. The TRL approach is derived from empirical models based on geometric parameters and observed driver behaviour with regard to lane choice. Sidra Intersection software includes roundabout capacity models developed in Australia and the US.

Research on Australian roundabouts was conducted in the 1980s at the Australian Road Research Board (ARRB).<ref>{{cite book|url=http://www.arrb.com.au/Information-services/Publications.aspx|title=Effectiveness Audit of ARRB Intersection Capacity Research|location=Research Report ARR 242. ARRB Transport Research Ltd, Vermont South, Australia|author=Taylor, M.P., Barton, E.V., Bliss, J. and O'Brien, A.P. (1993)|url-status=dead|archive-url=https://web.archive.org/web/20160227020155/https://arrb.com.au/Information-services/Publications.aspx|archive-date=27 February 2016}}</ref> Its analytical capacity and performance models differ from the TRL model significantly, following a lane-based gap-acceptance theory including geometric parameters.

Research on U.S. roundabouts sponsored by the [[Transportation Research Board]] (TRB) and [[Federal Highway Administration]] (FHWA) culminated in a capacity model that was included in the ''[[Highway Capacity Manual]]'' (HCM) Edition 6<ref>{{cite book|url=http://www.trb.org/publications/hcm6e.aspx|title=Highway Capacity Manual, Sixth Edition: A Guide for Multimodal Mobility Analysis|author=TRB (2016)|location= Transportation Research Board, National Research Council, Washington, DC, US}}</ref> and the ''TRB-FHWA Roundabout Informational Guide'' ([[NCHRP]] Report 672).<ref>{{cite book|url=http://www.trb.org/Main/Blurbs/164470.aspx|title=Roundabouts: An Informational Guide |author=TRB|date=2010 |location=NCHRP Report 672. Transportation Research Board, National Research Council, Washington, D.C., US, in cooperation with US Department of Transportation, Federal Highway Administration|doi=10.17226/22914 |isbn=978-0-309-15511-3 }}</ref> The HCM Edition 6 model is based on lane-based gap-acceptance theory. A recent NCHRP survey of US state transport agencies found that [[Sidra Intersection]] is the most widely used software tool in the US for roundabout analysis.<ref>{{cite book|url=https://www.nap.edu/catalog/23477/roundabout-practices|title=''Roundabout Practice, A Synthesis of Highway Practice''|publisher=  Transportation Research Board|year=2016|location=National Cooperative Highway Research Program, NCHRP SYNTHESIS 488. Washington DC, US.|doi=10.17226/23477|isbn=978-0-309-27208-7 |last1=Pochowski |first1=Alek |last2=Paul |first2=Andy |last3=Rodegerdts |first3=Lee A. }}</ref>