Roundabout
Overview
 
A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world. It is similar to traffic circle
Traffic circle
A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...

s that are primarily found in the United States, except that in a roundabout entering traffic must always yield to traffic already in the circle, whereas in a traffic circle entering traffic is either controlled by stop signs, traffic signals, or is not formally controlled at all.
Numerous circular junctions existed before the advent of roundabouts, including the 1907 Place de l'Etoile
Place de l'Étoile
The Place Charles de Gaulle, , historically known as the Place de l'Étoile , is a large road junction in Paris, France, the meeting point of twelve straight avenues including the Champs-Élysées which continues to the east. It was renamed in 1970 following the death of General and President Charles...

 around the Arc de Triomphe
Arc de Triomphe
-The design:The astylar design is by Jean Chalgrin , in the Neoclassical version of ancient Roman architecture . Major academic sculptors of France are represented in the sculpture of the Arc de Triomphe: Jean-Pierre Cortot; François Rude; Antoine Étex; James Pradier and Philippe Joseph Henri Lemaire...

in Paris, the 1904 Columbus Circle
Columbus Circle
Columbus Circle, named for Christopher Columbus, is a major landmark and point of attraction in the New York City borough of Manhattan, located at the intersection of Eighth Avenue, Broadway, Central Park South , and Central Park West, at the southwest corner of Central Park. It is the point from...

 in New York City, and several circles within Washington, DC.
Encyclopedia
A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world. It is similar to traffic circle
Traffic circle
A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...

s that are primarily found in the United States, except that in a roundabout entering traffic must always yield to traffic already in the circle, whereas in a traffic circle entering traffic is either controlled by stop signs, traffic signals, or is not formally controlled at all.

History

Numerous circular junctions existed before the advent of roundabouts, including the 1907 Place de l'Etoile
Place de l'Étoile
The Place Charles de Gaulle, , historically known as the Place de l'Étoile , is a large road junction in Paris, France, the meeting point of twelve straight avenues including the Champs-Élysées which continues to the east. It was renamed in 1970 following the death of General and President Charles...

 around the Arc de Triomphe
Arc de Triomphe
-The design:The astylar design is by Jean Chalgrin , in the Neoclassical version of ancient Roman architecture . Major academic sculptors of France are represented in the sculpture of the Arc de Triomphe: Jean-Pierre Cortot; François Rude; Antoine Étex; James Pradier and Philippe Joseph Henri Lemaire...

in Paris, the 1904 Columbus Circle
Columbus Circle
Columbus Circle, named for Christopher Columbus, is a major landmark and point of attraction in the New York City borough of Manhattan, located at the intersection of Eighth Avenue, Broadway, Central Park South , and Central Park West, at the southwest corner of Central Park. It is the point from...

 in New York City, and several circles within Washington, DC. However, the operating and entry characteristics of these circles differed considerably from modern roundabouts. The first British roundabout was built in Letchworth Garden City in 1903, making it the first in the world. It was originally intended partly as a traffic island for pedestrians. In the early 20th century, numerous traffic circle junctions were constructed in the United States, particularly in the northeast states. There are many instances of traffic circles in the US that predate the modern roundabout, like the ones that can be found in Atherton California.

At the beginning of the 21st century, roundabouts are in widespread use in Europe. France, for instance, had more than 30,000 roundabouts in 2010.

Modern roundabout

A "modern roundabout" is a type of circular junction that was developed by the UK's Transport Research Laboratory
Transport Research Laboratory
TRL is a British transport consultancy and research organisation based at Wokingham Berkshire with approximately 500 staff. TRL is owned by the Transport Research Foundation , which is overseen by 80 sector members from the transport industry. TRL also own small UK regional offices situated in...

in the mid twentieth century, in which road traffic must travel in one direction around a central island and priority is given to the circulating flow. Signs usually direct traffic entering the circle to slow down and give the right of way.

These junctions are called "modern roundabouts" in order to emphasise the distinction from older circular junction types which had different design characteristics and rules of operation. Older designs, called "traffic circle
Traffic circle
A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...

s" or "rotaries", are typically larger, operate at higher speeds, and often give priority to entering traffic. In some cases, the term "traffic circle" has been used to describe roundabouts in North America. The originally British term "roundabout" is now often used in North America too by officials and engineers, but it remains rare in general US usage though commonplace elsewhere.

In countries where vehicles keep to the right, the traffic flow around the central island of a roundabout is anti- (or counter-) clockwise
Clockwise
Circular motion can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top...

; where they keep to the left, it is clockwise
Clockwise
Circular motion can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top...

.

Statistically, roundabouts are safer for drivers and pedestrians than both traffic circles and intersections. Because low speeds are required for traffic entering roundabouts they are usually not used on controlled-access highways but may be used on lower grades of highway such as limited-access road
Limited-access road
A limited-access road known by various terms worldwide, including limited-access highway, dual-carriageway and expressway, is a highway or arterial road for high-speed traffic which has many or most characteristics of a controlled-access highway , including limited or no access to adjacent...

s. When such roads are redesigned to take advantage of roundabout principles, steps are taken to reduce the speed of traffic, such as curving the approaches.

Modern roundabouts are common place throughout the world, in particularly Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

, Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....

, Cyprus
Cyprus
Cyprus , officially the Republic of Cyprus , is a Eurasian island country, member of the European Union, in the Eastern Mediterranean, east of Greece, south of Turkey, west of Syria and north of Egypt. It is the third largest island in the Mediterranean Sea.The earliest known human activity on the...

, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, Hungary
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...

, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

, Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

, Luxembourg
Luxembourg
Luxembourg , officially the Grand Duchy of Luxembourg , is a landlocked country in western Europe, bordered by Belgium, France, and Germany. It has two principal regions: the Oesling in the North as part of the Ardennes massif, and the Gutland in the south...

, Malaysia, Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

, the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

, Qatar
Qatar
Qatar , also known as the State of Qatar or locally Dawlat Qaṭar, is a sovereign Arab state, located in the Middle East, occupying the small Qatar Peninsula on the northeasterly coast of the much larger Arabian Peninsula. Its sole land border is with Saudi Arabia to the south, with the rest of its...

, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

, the United Arab Emirates
United Arab Emirates
The United Arab Emirates, abbreviated as the UAE, or shortened to "the Emirates", is a state situated in the southeast of the Arabian Peninsula in Western Asia on the Persian Gulf, bordering Oman, and Saudi Arabia, and sharing sea borders with Iraq, Kuwait, Bahrain, Qatar, and Iran.The UAE is a...

, and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

. Half of the world's roundabouts are in France (over 30,000 as of 2008).

Difference from traffic circles

Following research by the Transport Research Laboratory
Transport Research Laboratory
TRL is a British transport consultancy and research organisation based at Wokingham Berkshire with approximately 500 staff. TRL is owned by the Transport Research Foundation , which is overseen by 80 sector members from the transport industry. TRL also own small UK regional offices situated in...

, which found that circular junctions with certain geometric characteristics and traffic control schemes tended to be safer than those without them, the United Kingdom introduced the rule in 1966 that entering traffic must always give way to traffic already on the roundabout.

Although the term roundabout is sometimes used for a traffic circle even in the United States, U.S. traffic engineers now make the distinction that in a roundabout entering traffic must always yield to traffic already in the circle, whereas in a traffic circle entering traffic is controlled by Stop signs, or is not formally controlled, although some states are exceptions, notably New York, which follows the "yield" rule although naming them Traffic Circles. In their usage, circular junctions that have the following characteristics are roundabouts and those that do not are considered traffic circle
Traffic circle
A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...

s:
  • Roundabouts require entering drivers to give way to all traffic within the roundabout, regardless of lane position, while traffic circles typically allow traffic to enter alongside traffic circulating in an inner lane without consequence.
  • Generally, exiting directly from the inner lane of a multi-lane roundabout is permitted, and such exiting traffic has the right-of-way over entering traffic. By contrast, exiting from the inner lane of a traffic circle is usually not permitted without first executing a lane change to the outside of the circle. Massachusetts, where older traffic circles, or rotaries, are commonplace, has a dwindling number of exceptions.
  • Deflection on entry is used to maintain low speed operation in roundabouts. Drivers must manoeuvre (are deflected) around the splitter islands and the central island, at speeds of 15–25 mph (24.1–40.2 km/h). Many older traffic circle
    Traffic circle
    A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...

     junctions allow entry at higher speeds due to the lack of deflection, or require a stop and a 90-degree turn to enter, creating a large difference in speed between entering and circulating traffic which can make it difficult for entering drivers to find suitable gaps in heavy traffic.
  • Pedestrians are usually prohibited from the central island of roundabouts, and the crosswalk for pedestrians and some cyclists is withdrawn from the junction by at least the length of one vehicle.
  • All vehicles circulate around the central island of a roundabout in the same direction, which is determined by whether traffic drives to the right or the left. In left-hand traffic countries the circulation is clockwise; in those that drive to the right, it is anticlockwise.
  • Modern multi-lane roundabouts are typically less than 250 feet (75 metres) in diameter, although signalised roundabouts and roundabout interchange
    Roundabout interchange
    A roundabout interchange is a type of interchange between a controlled access highway such as a motorway or freeway, and a minor road, in which the slip roads to and from the motorway carriageways converge at a single roundabout, which is grade-separated from the motorway lanes with bridges...

    s may be considerably larger.


A large number of traffic circles have been converted to other types of junctions. Several have been converted to roundabouts, now meeting modern roundabout design standards, including the former Kingston
Kingston, New York
Kingston is a city in and the county seat of Ulster County, New York, USA. It is north of New York City and south of Albany. It became New York's first capital in 1777, and was burned by the British Oct. 16, 1777, after the Battles of Saratoga...

 traffic circle in New York and several in New Jersey. Others have been converted to a series of signalised intersections, such as the Drum Hill Rotary in Chelmsford, Massachusetts
Chelmsford, Massachusetts
Chelmsford is a suburban town in Middlesex County, Massachusetts in the Greater Boston area. As of the 2010 United States Census, the town's population was 33,802. The Census Bureau's 2008 population estimate for the town was 34,409, ranking it 14th in population among the 54 municipalities in...

, which is now six lanes wide, with traffic lights on all four corners. The formerly oval-shaped rotary is now smaller and round-shaped.

Terminology

In the U.S., many people use the terms "roundabout", "traffic circle", and "rotary" interchangeably, and they are defined as synonyms in dictionaries. Many old traffic circles remain in the Northeastern United States
Northeastern United States
The Northeastern United States is a region of the United States as defined by the United States Census Bureau.-Composition:The region comprises nine states: the New England states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont; and the Mid-Atlantic states of New...

. Since many of the older junction forms have unfavourable safety records, transportation professionals are careful to use "roundabout" when referring to newer designs and "traffic circle" or "rotary" when referring to ones that do not meet the criteria listed above.

The term "traffic circle" is not used in the United Kingdom, where most circular junctions meet the U.S. technical criteria for roundabouts. The U.K. does, however, have roundabout variants such as mini-roundabouts and magic-roundabouts — see below for the distinctions from the type of junction generally referred to here as a roundabout.e more precise term, modern roundabout is used often to differentiate more carefully.

Modern roundabout history

Although numerous circular junctions existed before the advent of modern roundabouts, the widespread use of the modern roundabout began when Transport Research Laboratory
Transport Research Laboratory
TRL is a British transport consultancy and research organisation based at Wokingham Berkshire with approximately 500 staff. TRL is owned by the Transport Research Foundation , which is overseen by 80 sector members from the transport industry. TRL also own small UK regional offices situated in...

 engineers re-engineered circular intersections during the 1960s and Frank Blackmore
Frank Blackmore (traffic engineer)
Frank Blackmore, OBE, DFC was a British traffic engineer. Blackmore was also the inventor of the mini-roundabout....

 led the development of the offside priority rule and subsequently also invented the mini roundabout to overcome its limitations of capacity and for safety issues. The rule was adopted as mandatory in Britain for all new roundabouts in November 1966. Unlike traffic circles, traffic approaching roundabouts is normally required to give priority to circulating and exiting traffic (this yield requirement has, however, been the law in the US state of New York since the 1920s) and to eliminate much of the driver confusion associated with traffic junctions and waiting queues associated with junctions that have traffic light
Traffic light
Traffic lights, which may also be known as stoplights, traffic lamps, traffic signals, signal lights, robots or semaphore, are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic...

s. Roughly the same size as signalled intersections with the same or sometimes a higher capacity, separate incoming and outgoing traffic with pedestrian islands to encourage slower and safer speeds (see traffic calming
Traffic calming
Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

).

They were much less common in the United States, where they started seeing limited use in the 1990s and face some opposition from a population mostly unaccustomed to them. In 2011, there were about 3,000 U.S. roundabouts, and their number is growing steadily. The first modern roundabout in the United States was constructed in Summerlin, Nevada
Summerlin, Nevada
Summerlin is an affluent master-planned community under development by The Howard Hughes Corporation in the Las Vegas metropolitan area of Nevada near the Spring Mountains and Red Rock Canyon National Conservation Area. It lies partially within the city limits of Las Vegas, Nevada, and in...

 in 1990. This roundabout occasioned a significant amount of "dismay" from residents, and a local news program several years later said about it, "Even police agree, they (roundabouts) can be confusing at times." Roundabouts have since become increasingly common in North America. Carmel, Indiana
Carmel, Indiana
Carmel is a city in Hamilton County, Indiana, United States located immediately north of Indianapolis, Indiana. The population was 79,191 at the 2010 census, and is one of the most affluent communities in the Midwest....

 has more than 77 roundabouts and hosted the 2011 Transportation Research Board's (TRB) National Roundabout Conference.

Safety

Roundabouts are safer than both traffic circles and junctions—having 40% fewer vehicle collisions, 80% fewer injuries and 90% fewer serious injuries and fatalities (according to a study of a sampling of roundabouts in the United States, when compared with the junctions they replaced). Roundabouts also reduce points of conflict between pedestrians and motor vehicles and are therefore considered to be safer for them, additionally, most feature a safety island refuge where pedestrians can pause mid-crossing. However, roundabouts, especially larger ones with faster traffic, are unpopular with some cyclists (who do, of course, have the option of walking their bicycles in the pedestrian crosswalks). This problem is sometimes addressed at larger roundabouts by taking foot and bicycle traffic through a series of underpasses or alternate routes.

At traditional junctions with stop signs or traffic lights, the most serious accidents are right-angle, left-turn, or head-on collisions that can be severe because vehicles may be moving fast and collide at high angles of impact. Roundabouts virtually eliminate those types of crashes because vehicles all travel in the same direction and most crashes are glancing blows at low angles of impact.

While roundabouts can reduce crashes overall compared to other junction types, crashes involving cyclists may not experience similar reductions. An analysis of the New Zealand national crash database for the period 1996–2000 shows that cyclists were involved in 26% of the reported injury crashes at roundabouts, compared to 6% at traffic signals and 13% at priority controlled junctions. The New Zealand researchers propose that low vehicle speeds, circulatory lane markings, and mountable centre aprons for trucks can improve the safety of cyclists within roundabouts. These strategies are typically employed on modern roundabouts constructed in the United States.

The most common roundabout crash type for cyclists, according to the New Zealand study, involves a motor vehicle entering the roundabout and colliding with a cyclist who already is travelling around the roundabout (generally just over 50% of all cyclist/roundabout crashes fall into this category). The next most common crash type involves motorists leaving the roundabout, colliding with cyclists who are continuing further around the perimeter of the roundabout. Designs that have marked perimeter cycle lanes are found by research data to be even less safe than those without them, suggesting that in roundabouts cyclists should "take the lane", operating as a vehicle rather than tracking around the perimeter. The cure for this is applying the rule prohibiting overtaking and passing on the circular roadway to motor vehicles overtaking cyclists.

If the adjacent footpaths are not properly designed, there are increased risks for persons with visual impairments. This is because it is more difficult (than at a signalized intersection) to detect with hearing whether there is a gap in traffic adequate to cross. During the all-red interval at a signal, traffic comes to a stop, and blind pedestrians can tell by listening which direction gets the green light. Since there is often moving traffic at a roundabout, the sounds of non-conflicting traffic will mask gaps, or the sound of an idling vehicle whose driver has stopped to give way to the pedestrian.

This issue has led to a conflict in the United States between the visually impaired and civil engineering
Civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...

 communities; some in the visually impaired community have taken the position that roundabouts (rather than signal-controlled crossings) are acceptable only if there are pedestrian crossings with signalised control at each road connecting to a roundabout. Engineers point out that since vehicle speeds are slower, crossing gaps are more plentiful, drivers are more apt to give way, and pedestrian crashes are less severe than if the same driver had run a red light. However, the blind community considers this to be a civil rights
Civil rights
Civil and political rights are a class of rights that protect individuals' freedom from unwarranted infringement by governments and private organizations, and ensure one's ability to participate in the civil and political life of the state without discrimination or repression.Civil rights include...

 issue, not an engineering issue. While pedestrian crossings with traffic lights installed in roundabouts exist (see below), signalisation is normally used on large-diameter roundabout interchanges rather than small-diameter modern roundabouts. Signalisation would also substantially increase the cost of roundabout construction and maintenance (essentially, both types of junction being built at every junction). Furthermore, equipping a roundabout with traffic-halting lights would decrease its throughput considerably, thereby artificially reducing or even eliminating the design's main advantage over traditional signal-equipped junctions. Signalisation would also increase delays for most pedestrians during light traffic, since pedestrians would need to wait for the signal to change to legally cross.

Capacity and delays

The capacity of a roundabout varies based on the number of entry and circulating lanes, and also on more subtle geometry elements including entry angle and lane width. Also, like other types of junctions, the operational performance of a roundabout depends heavily on the flow volumes from various approaches. A single-lane roundabout can be expected to handle approximately 20,000 to 26,000 vehicles per day, while a two-lane roundabout can be expected to handle 40,000 to 50,000 vehicles per day.

Under many traffic conditions, an unsignalised roundabout can operate with less delay to users than traffic signal control or all-way stop control. Unlike all-way stop intersections, a roundabout does not require a complete stop by all entering vehicles, which reduces both individual delay and delays resulting from vehicle queues. A roundabout can also operate much more efficiently than a signalised junction because drivers are able to proceed when traffic is clear without the delay incurred while waiting for the traffic signal to change.

However, roundabouts can increase delays in locations where traffic would otherwise 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 normally not have to stop if the junction were signalised, because the traffic signals would provide a green signal to the busier road the majority of the time. When the volumes on the approach roadways are relatively balanced, a roundabout can reduce delay because each approach would otherwise encounter a red signal greater than half of the time if the junction were signalised.

Roundabouts can also reduce delays for pedestrians when compared to traffic signals, because pedestrians are able to cross during any safe gap rather than waiting for the traffic signal to provide the right-of-way to the pedestrian. During peak hours of congestion when large gaps are infrequent, the very slow speed of traffic entering and leaving the roundabout can compensate for the smaller gaps and facilitate pedestrian crossings.

TRL, the UK's Transport Research Laboratory
Transport Research Laboratory
TRL is a British transport consultancy and research organisation based at Wokingham Berkshire with approximately 500 staff. TRL is owned by the Transport Research Foundation , which is overseen by 80 sector members from the transport industry. TRL also own small UK regional offices situated in...

 later developed a mathematical model throughout the 1960s and 1970s to facilitate traffic engineers with the necessary knowledge to engineer and design Roundabouts. It was decided by the UK government to deliver this in the form of 'Assessment of Roundabout Capacity And DelaY' (ARCADY
Arcady
ARCADY is the acronym for . This software, produced by the Transport Research Laboratory , provides information on traffic flow including modelling capacity queues and delays at roundabouts...

). Several software packages now exist to help with calculating capacity and queues at roundabouts. These include ARCADY, RODEL and SIDRA INTERSECTION.

Cycle facilities at roundabouts

Research has shown that even in large circular junctions that lack modern roundabout design features, a high rate of bicycle/motor vehicle crashes occurs when bicyclists are riding around the outside. Design guidance for modern roundabouts recommends terminating cycle lanes well before the entrances, so bicyclists merge into the stream of motor traffic.

A 1992 study from the German Transport Ministry
Federal Ministry of Transport, Building and Urban Affairs (Germany)
The Federal Ministry of Transport, Building and Urban Development is a Ministry of Germany.It was created in 1998 by merger of the former Federal Ministry of Transport and the Federal Ministry of Regional Planning, Building and Urban Development, both established in 1949...

's research institute has cast particular light on this issue. The study found that bicyclists' risk is high in all such intersections, but it is much higher when the junction has a marked bicycle lane or sidepath around its outside (see "Marked perimeter cycle lanes" below). The results of this study concerning circular junctions are summarised on the web (in German, but partially translated below). A report about accidents at four-arm roundabouts was published by the UK Transport and Road Research Laboratory (TRRL) (now TRL
Transport Research Laboratory
TRL is a British transport consultancy and research organisation based at Wokingham Berkshire with approximately 500 staff. TRL is owned by the Transport Research Foundation , which is overseen by 80 sector members from the transport industry. TRL also own small UK regional offices situated in...

) in 1984.

Collisions typically occur when a motorist is entering or leaving the circular roadway. A motorist entering the circular roadway must give way to traffic in it, but such traffic will generally keep away from the outside of the circular roadway (as with a vehicle in the photo) if passing an entrance. A bicyclist close to the edge of the roadway is not in the usual position where an entering motorist expects to look for circulating traffic.

When exiting the circular roadway, a motorist must look ahead to steer, and to avoid colliding with another vehicle ahead or with pedestrian
Pedestrian
A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...

s on a footpath
Sidewalk
A sidewalk, or pavement, footpath, footway, and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade and is normally separated from the vehicular section by a curb...

. As the circular roadway curves away from the exit, the path of a vehicle exiting the circular roadway is relatively straight, and so the exiting motorist may often not need to slow substantially. However, if it is necessary to give way to a bicyclist riding around the outside, the exiting motorist must look toward the rear, to the outside of the intersection. With many vehicles, such as van
Van
A van is a kind of vehicle used for transporting goods or groups of people.In British English usage, it can be either specially designed or based on a saloon or sedan car, the latter type often including derivatives with open backs...

s, the driver's view in this direction is obstructed. The task burden of the motorist is therefore substantially increased if bicyclists ride around the outside. The resulting conflicts, and more frequent requirements for motorists to slow or stop, also reduce the efficiency of traffic flow which is one of the major advantages of the circular junctions. Cycle lanes around the outside of circular junctions are therefore falling out of favour.

Marked perimeter cycle lanes

An early attempt to deal with the problem was to mark preferential lanes for cyclists. With cycle lanes, bicyclists
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

 do not merge into the flow of motor traffic in the roundabout, but rather, they travel around the outside, relieving them of the requirement to merge. The coloured road surface and edge lines of the cycle lanes indicate that exiting motorists are required to give way to bicyclists at all locations where their paths may cross. As noted previously, this design has been found to be hazardous to cyclists and has fallen out of favour.

This form of roundabout was originally installed at St John's roundabout in Newbury, Berkshire
Newbury, Berkshire
Newbury is a civil parish and the principal town in the west of the county of Berkshire in England. It is situated on the River Kennet and the Kennet and Avon Canal, and has a town centre containing many 17th century buildings. Newbury is best known for its racecourse and the adjoining former USAF...

, England and at Museum Road, Portsmouth
Portsmouth
Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...

, England. The St John's roundabout in Newbury is still marked with perimeter cycle lanes. The cycle lanes on the roundabout at Museum Road, Portsmouth have been removed and, instead, the carriageway
Carriageway
A carriageway consists of a width of road on which a vehicle is not restricted by any physical barriers or separation to move laterally...

 has been narrowed to encourage drivers and cyclists to circulate together.

Modern design guidance

The special features of modern roundabouts, including splitter/diverter islands and limited diameter of the circular roadway, decrease the speed of motor traffic and so reduce the risk of collisions for motorists as well as cyclists below that of conventional junctions. Design guidance for modern roundabouts recommends terminating cycle lanes well before the entrances, so cyclists merge into the stream of motor traffic. Cyclists who lack the confidence to do this may use the footpaths as pedestrians. Modern design guidance also recommends placing the footpath crossings far enough from the roundabout so that at least one exiting vehicle can wait without blocking the circular roadway. A roundabout with two lanes should place the footpath crossing two car lengths from the junction.
The roundabout at the Brown Road/202 interchange includes such a design. On-street pavement markings indicate bicyclists may enter sidewalk at end of bike lane. Bicyclists who choose to travel on the wide sidewalk cross roundabout arms perpendicularly some distance removed from the circle. Each crossing crosses two lanes, one in each direction. A median refuge is provided to allow pedestrians and bicyclists to cross one lane at a time.

The reason for placing crossings away from the circle is to give motorists more space and time to yield to cyclists and pedestrians who cross in them, and to increase the likelihood that crosswalk users and motorists will see each other.

Bicycle-pedestrian roundabouts

The same features that make roundabouts an attractive option for roadway junctions have led to their use at junctions of multi-use trails. The University of California, Davis
University of California, Davis
The University of California, Davis is a public teaching and research university established in 1905 and located in Davis, California, USA. Spanning over , the campus is the largest within the University of California system and third largest by enrollment...

 and Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...

 both have built bicycle-pedestrian roundabouts. Roundabouts are used on off-road bicycle trails in Florida, Colorado and Alaska.

See the United States DOT
United States Department of Transportation
The United States Department of Transportation is a federal Cabinet department of the United States government concerned with transportation. It was established by an act of Congress on October 15, 1966, and began operation on April 1, 1967...

 publication, Roundabouts: An Informational Guide.

Advantages of roundabouts

  • Roundabouts are safer than signal controlled junctions, with accidents usually occurring at a slower speed and at a slight angle instead of right-angle or rear end collisions at junctions.
  • Roundabouts allow U-turns within the normal flow of traffic, which are often not possible at other forms of junction.
  • In general, roundabouts substantially reduce congestion and delays as vehicles are not required to perform a complete stop.
  • Compared to intersections, Roundabout operate more efficiently and thus reduce delays and congestion as they are not at the whim of an artificially induced delay by traffic signals. Efficiency is gained by a direct response from the driver to the traffic conditions without any restrictions set by traffic signals - i.e. drivers can proceed when traffic is clear without the delay incurred by a traffic signal.

Public opinion

In the United States, municipalities introducing new roundabouts often are met with some degree of public resistance just as in the United Kingdom in the 1960s. Drivers may be unfamiliar with roundabouts initially; however, survey
Statistical survey
Survey methodology is the field that studies surveys, that is, the sample of individuals from a population with a view towards making statistical inferences about the population using the sample. Polls about public opinion, such as political beliefs, are reported in the news media in democracies....

s show that public opinion
Public opinion
Public opinion is the aggregate of individual attitudes or beliefs held by the adult population. Public opinion can also be defined as the complex collection of opinions of many different people and the sum of all their views....

 improves as drivers gain more experience with roundabouts. A 1998 survey of municipalities that built roundabouts found public opinion prior to construction as 68% opposed; afterwards it was 73% in favour. A 2007 survey of citizens found public support at 22% to 44% prior to construction, and several years after it was 57% to 87%.

Special types

Large roundabouts such as those used at motorway junctions typically have two to six lanes around the central hub, and may have traffic lights regulating flow.

Some roundabouts have a divider between traffic turning from one road onto an adjacent one, and traffic within the roundabout, enabling those making such turns to bypass the roundabout entirely.

Gyratory system

The term "gyratory" (for example, Hanger Lane gyratory) is sometimes used in the United Kingdom when a roundabout is large and has non-standard lane markings or priorities, or when there are buildings on the central island; in fact, they are more like traffic circles.

Mini-roundabouts

After developing the offside priority rule, Frank Blackmore
Frank Blackmore (traffic engineer)
Frank Blackmore, OBE, DFC was a British traffic engineer. Blackmore was also the inventor of the mini-roundabout....

, of the UK's Transport Research Laboratory
Transport Research Laboratory
TRL is a British transport consultancy and research organisation based at Wokingham Berkshire with approximately 500 staff. TRL is owned by the Transport Research Foundation , which is overseen by 80 sector members from the transport industry. TRL also own small UK regional offices situated in...

, turned his attention to the possibility of a new type of roundabout that could be utilised at sites with limited space to use a conventional roundabout.
Mini-roundabouts exist at these smaller junctions to avoid the use of signals, stop signs or the necessity to give way in favour of one road of traffic. Mini-roundabouts can be a painted circle or a low dome but must be fully traversable. Painted roundabouts and low domes can easily be driven over by most vehicles, which many motorists will do when there is no other traffic, but the practice is dangerous if other cars are present. Mini-roundabouts work in the same way as larger roundabouts in terms of right of way but can give different performance with regard to driver behaviour. Mini-roundabouts are sometimes grouped in pairs (a double mini-roundabout) or in "chains", making navigation of otherwise awkward junctions easier. In some countries there are different road signs used to distinguish mini roundabouts from larger ones.

Mini-roundabouts are common in the UK and Ireland, as well as Irapuato
Irapuato, Guanajuato
Irapuato is a Mexican city located at the foot of the Arandas mountain , in the south central region of the state of Guanajuato. It lies between the Silao River and the Guanajuato River, a tributary of the Lerma River, at 1,724 m above sea level. It is located at...

 in Mexico and Mount Royal and Rosedale in Calgary, Canada. Kemptville, Ontario, a small town located in Canada, has the record for the most roundabouts in Ontario, with a record of three on one highway. Most people who do not live in Kemptville find it difficult to use the roundabouts properly. This is the leading source of road rage in Kemptville.

A slightly larger version of a mini-roundabout, sometimes called a "small or midi roundabout", is designed with a raised centre surrounded by a sloped "overrun area" of a different colour from the roadway and up to a metre wide called a "truck apron" or a "mountable apron". The truck apron's design discourages small vehicles from taking a shortcut over it while at the same time allowing the mini-roundabout to more easily accommodate the turning radius of larger vehicles (such as a truck which may have to navigate the roundabout).

In the UK the maximum permissible diameter of the central painted circle of a mini-roundabout is 4m. Whilst it may be physically possible, it is illegal for vehicles which are able to circulate around the central circle of the roundabout to go over the painted circle, or around the wrong way. Vehicles should treat the painted circle like a solid island and proceed around it. (In practice, many motorists ignore these rules, especially when traffic is light.) Some local authorities have installed double white lines around the painted circle to indicate this, but these are not permitted under UK traffic signs regulations without authorisation from the Secretary of State for Transport
Secretary of State (United Kingdom)
In the United Kingdom, a Secretary of State is a Cabinet Minister in charge of a Government Department ....

 . The centre island also must be able to be over-run by larger vehicles.

At Hatton Cross roundabout, close to London Heathrow Airport
London Heathrow Airport
London Heathrow Airport or Heathrow , in the London Borough of Hillingdon, is the busiest airport in the United Kingdom and the third busiest airport in the world in terms of total passenger traffic, handling more international passengers than any other airport around the globe...

, five small ‘mini-roundabouts’ have been constructed where the roads join/leave the main roundabout, allowing traffic to circle the main roundabout in both directions - clockwise in the outer lane(s) and anti-clockwise in the inner lanes.

Raindrop roundabouts

These roundabouts do not form a complete circle and are in a "raindrop" shape. They are appearing at U.S. Interstate
Interstate Highway System
The Dwight D. Eisenhower National System of Interstate and Defense Highways, , is a network of limited-access roads including freeways, highways, and expressways forming part of the National Highway System of the United States of America...

 interchanges to provide a free-flowing left turn to the on-ramps and eliminating the need for turn signals and lanes. Since the entry and exit slip roads are one-way, a complete circle is unnecessary. This means that drivers entering the roundabout from the bridge do not need to give way and prevents queuing on narrow, two-lane bridges. These roundabouts have been used at dumbbell
Bowtie (road)
The Bowtie is an alternative to the Michigan left format that uses roundabouts on the cross street. Left turns are prohibited atthe main intersection, which therefore requires only a two-phase signal. Vehicles yield upon entry to the roundabout, but if the roundabout has only two entrances, the...

 roundabout junctions, replacing traffic signals that are inefficient without a turning lane. Several junctions along Interstate 70
Interstate 70
Interstate 70 is an Interstate Highway in the United States that runs from Interstate 15 near Cove Fort, Utah, to a Park and Ride near Baltimore, Maryland. It was the first Interstate Highway project in the United States. I-70 approximately traces the path of U.S. Route 40 east of the Rocky...

 near Avon, Colorado
Avon, Colorado
Avon is a Home Rule Municipality that is the most populous town in Eagle County, Colorado, United States. The population was 5,561 at the 2000 census. Avon is the gateway to the Beaver Creek Resort which lies about two miles south of the town. It was the previous site of Vail Resorts before the...

 use teardrop roundabouts.

Turbo roundabouts

In the Netherlands and Belgium, a relatively new type of roundabout is built increasingly often. It provides a forced spiralling flow of traffic, thus requiring motorists to choose their direction before entering the roundabout. By eliminating many conflicting paths and choices on the roundabout itself, traffic safety is increased, as well as speed, and as a result, capacity. A turbo roundabout does not allow travelling a full circle.

Several variations of the turbo roundabout exist. The basic turbo roundabout shape is designed for where a major road crosses a road with less traffic.

Turbo roundabouts were originally built with raised lane separators. Newer implementations with only lane markings exist, for efficiency (regarding safety, speed and capacity) of the design by reducing safety risk to large and small vehicles and enabling maintenance such as snow ploughs. Similar roundabouts, with spiralling lane markings, have been used for many years in the UK e.g. the A176/A127 (eastbound) at Basildon, Essex.

According to micro-simulation, a two-lane roundabout with free right turns should offer 12-20% greater traffic flow than a conventional, three-lane roundabout of the same size. The reason offered by authors Ir. Isaak Yperman and Prof. Ir. Ben Immers is that there is less weaving in a turbo, making entering and exiting more predictable. Because there are only ten points of conflict (compared with 8 for a conventional single lane roundabout, or between 32 and 64 with traffic signal control), it is often expected that this design is safer, as well. At least 70 have been built in the Netherlands, while many turbos (or similar, lane splitting designs) can be found in southeast Asia.

Multi-lane roundabouts in the United States of America are typically required to be striped with spiral markings, as most states follow the federal Manual on Uniform Traffic Control Devices
Manual on Uniform Traffic Control Devices
The Manual on Uniform Traffic Control Devices is a document issued by the Federal Highway Administration of the United States Department of Transportation to specify the standards by which traffic signs, road surface markings, and signals are designed, installed, and used...

 or develop a state-level manual subject to the approval of the federal government.

Roundabouts on motorways

Roundabouts are generally not appropriate for placement on motorway or freeway mainlines because the purpose of such facilities is to provide for uninterrupted traffic flow. However, roundabouts are often used for the junction between the slip roads and the intersecting road. A single roundabout, grade separated
Grade separation
Grade separation is the method of aligning a junction of two or more transport axes at different heights so that they will not disrupt the traffic flow on other transit routes when they cross each other. The composition of such transport axes does not have to be uniform; it can consist of a...

 from the mainlines, may be used to create a roundabout interchange
Roundabout interchange
A roundabout interchange is a type of interchange between a controlled access highway such as a motorway or freeway, and a minor road, in which the slip roads to and from the motorway carriageways converge at a single roundabout, which is grade-separated from the motorway lanes with bridges...

. This type of junction is common in the UK and Ireland. Alternatively, separate roundabouts may also be used at the slip road intersections of a diamond interchange
Diamond interchange
A diamond interchange is a common type of road junction, used where a freeway crosses a minor road. The freeway itself is grade-separated from the minor road, one crossing the other over a bridge...

 to create what is often referred to as a "dumbbell interchange", which is increasingly common in both Europe and North America due to its reduced need for wide or multiple bridges.

An additional use of roundabouts for junctions is the 3-level stacked roundabout — this is a roundabout interchange
Roundabout interchange
A roundabout interchange is a type of interchange between a controlled access highway such as a motorway or freeway, and a minor road, in which the slip roads to and from the motorway carriageways converge at a single roundabout, which is grade-separated from the motorway lanes with bridges...

 where both of the roadway mainlines are grade separated. In the United Kingdom, the M25
M25 motorway
The M25 motorway, or London Orbital, is a orbital motorway that almost encircles Greater London, England, in the United Kingdom. The motorway was first mooted early in the 20th century. A few sections, based on the now abandoned London Ringways plan, were constructed in the early 1970s and it ...

/A3
A3 road
The A3, known as the Portsmouth Road for much of its length, is a dual carriageway, or expressway, which follows the historic route between London and Portsmouth passing close to Kingston upon Thames, Guildford, Haslemere and Petersfield. For much of its length, it is classified as a trunk road...

, M8/M73 and A1(M)/M18 interchanges are examples of this type. These junctions, however, have less capacity than a full free-flow interchange
Free-flow interchange
A free-flow interchange is an interchange in which all roads are grade-separated, and where movement from one road to another does not require the driver to stop for traffic...

. A similar design to this is the three-level diamond interchange.

Most junctions on Dublin's M50 motorway C-road use a standard roundabout interchange — although several such junctions have a greater volume of traffic than the capacity such roundabouts can accommodate. In Northern Ireland
Northern Ireland
Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

, the junction between the M1 and M12 (Craigavon connector motorway) is via a standard roundabout with a raised centre, 3 onslips and 3 offslips, and 2 lanes.

In the city of Malmö
Malmö
Malmö , in the southernmost province of Scania, is the third most populous city in Sweden, after Stockholm and Gothenburg.Malmö is the seat of Malmö Municipality and the capital of Skåne County...

, Sweden, there is a roundabout connecting two motorways, Autostradan from Lund
Lund
-Main sights:During the 12th and 13th centuries, when the town was the seat of the archbishop, many churches and monasteries were built. At its peak, Lund had 27 churches, but most of them were demolished as result of the Reformation in 1536. Several medieval buildings remain, including Lund...

, and the Inner ring road. It is signposted as a motorway throughout this roundabout. Today these two motorways are considered local, but before the year 2000 they were part of the European roads E6
European route E6
European route E 6 is the designation for the main north-south road in Norway, and the west coast of Sweden, running from the southern tip of Sweden, at Trelleborg, into Norway and through almost all of the country north to Finnmark. The route ends close to the Norwegian border with Russia...

, E20
European route E20
The European route E 20 is part of the United Nations International E-road network.It runs roughly west-east through Ireland, the United Kingdom, Denmark, Sweden, Estonia and finally Russia. The length is . The road is not continuous, at three points, a sea crossing is required. ...

 and E22
European route E22
The European route E 22 is one of the longest European routes. It has a length of about . Many of the E-roads have been extended into Asia since the year 2000; the E 22 was extended on 24 June 2002.-United Kingdom:...

.

In the Netherlands, A6 motorway
A6 motorway (Netherlands)
The A6 motorway is a motorway in the Netherlands. It is just over 100 kilometers in length and it connects the A1 motorway at interchange Muiderberg with the A7 motorway at interchange Joure....

 and A7 motorway
A7 motorway (Netherlands)
The A7 motorway is a motorway in the Netherlands connecting Zaandam, via the Afsluitdijk, Sneek and Groningen to the German border near Bad Nieuweschans. The entire road is part of the European route E22, with exception of the first kilometre, between the terminus in Zaandam and the interchange...

 cross near Joure
Joure
Joure is a town in the Dutch province of Friesland. With 13,000 inhabitants, it is the largest town in the municipality of Skarsterlân.-History:...

 using a roundabout. For the junction between the A200 and the A9
A9 motorway (Netherlands)
The A9 motorway is a motorway in the Netherlands. The motorway starts off by going from the A1 at Diemen to the A2 at junction 'Holendrecht'...

 a 3-level stacked roundabout is used. Near Eindhoven (the Leenderheide junction), the junction for the A2
A2 motorway (Netherlands)
The A2 motorway is a motorway in the Netherlands. It is one of the busiest highways in the Netherlands. The road connects the city of Amsterdam, near the interchange Amstel, with the Belgian border, near Maastricht and Liège , and the Belgian road A25....

 is done with a roundabout. An overpass is built for the A67 from Antwerp to Germany.

Roundabout interchanges are sometimes confused with rotary interchanges, which operate with traffic circle
Traffic circle
A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...

s rather than roundabouts. Rotary interchanges are common in New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...

, particularly in the state of Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...

, but a European example of a rotary interchange may be found in Hinwil, Switzerland
Hinwil
Hinwil is a municipality in the district of Hinwil in the canton of Zürich in Switzerland.- History :The village Hinwil from which the later municipality took its name is first mentioned in 745 as Hunichinwilari, in a donation made by Beata and Landolt to the Abbey of Saint Gall...

.

Controlled roundabouts

Some bridges on Beijing's 2nd Ring Road
2nd Ring Road (Beijing)
Encircling the centre of Beijing, the 2nd Ring Road is just a few kilometres away from the city centre and is a convenient alternative road to avoid congestion there. One can divide the road into two parts: the original ring road , and the newly extended ring road...

 are controlled by traffic lights. While it may appear to defy the roundabout system at first, it works well to control the flow of traffic on the bridges, which themselves are two viaducts creating a roundabout suspended over the ring road itself.

Signal controlled
Traffic light
Traffic lights, which may also be known as stoplights, traffic lamps, traffic signals, signal lights, robots or semaphore, are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic...

 roundabouts are common in Great Britain and Ireland, where they have been introduced in an attempt to alleviate traffic problems at over-capacity roundabout junctions or to prevent some flows of traffic dominating others (around the M50 in Dublin for example).

"Magic" roundabouts

The town of Swindon in Wiltshire
Wiltshire
Wiltshire is a ceremonial county in South West England. It is landlocked and borders the counties of Dorset, Somerset, Hampshire, Gloucestershire, Oxfordshire and Berkshire. It contains the unitary authority of Swindon and covers...

, England, is known for its "Magic Roundabout
Magic Roundabout (Swindon)
The Magic Roundabout in Swindon, England was constructed in 1972 and consists of five mini-roundabouts arranged in a circle. It is located near the County Ground, home of Swindon Town F.C. Its name comes from the popular children's television series The Magic Roundabout...

". This roundabout is at a junction of five roads and consists of a two-way road around the central island with five mini-roundabouts where it meets the incoming roads. Traffic may proceed around the main roundabout either clockwise via the outer lanes, or anticlockwise using the inner lanes next to the central island. At each mini-roundabout the usual clockwise flow applies.

Similar systems are found in various places in England, most famously the Moor End roundabout
Magic Roundabout (Hemel Hempstead)
The Magic Roundabout in Hemel Hempstead, Hertfordshire, England is the familiar name given to a complex road junction also known as the Moor End or Plough roundabout. The familiar name comes from the children's television programme of the same name and is also used for a similar junction in Swindon...

 in Hemel Hempstead
Hemel Hempstead
Hemel Hempstead is a town in Hertfordshire in the East of England, to the north west of London and part of the Greater London Urban Area. The population at the 2001 Census was 81,143 ....

 (Hertfordshire
Hertfordshire
Hertfordshire is a ceremonial and non-metropolitan county in the East region of England. The county town is Hertford.The county is one of the Home Counties and lies inland, bordered by Greater London , Buckinghamshire , Bedfordshire , Cambridgeshire and...

), which has six intersections; but also in High Wycombe
High Wycombe
High Wycombe , commonly known as Wycombe and formally called Chepping Wycombe or Chipping Wycombe until 1946,is a large town in Buckinghamshire, England. It is west-north-west of Charing Cross in London; this figure is engraved on the Corn Market building in the centre of the town...

 (Buckinghamshire
Buckinghamshire
Buckinghamshire is a ceremonial and non-metropolitan home county in South East England. The county town is Aylesbury, the largest town in the ceremonial county is Milton Keynes and largest town in the non-metropolitan county is High Wycombe....

), the Denham Roundabout
Denham Roundabout
The Denham Roundabout is a large road intersection to the west of London, at junction 1 on the M40 motorway.When Western Avenue was originally built, it ended at a point west of Uxbridge at the intersection of the road from Uxbridge towards Gerrards Cross and High Wycombe with the road from...

 in Denham
Denham, Buckinghamshire
Denham is a village and civil parish in the South Buckinghamshire district of Buckinghamshire, England. It is north west of Uxbridge and north of junction 1 of the M40 motorway. Denham contains the Buckinghamshire Golf Club.-Origin:...

 (Buckinghamshire
Buckinghamshire
Buckinghamshire is a ceremonial and non-metropolitan home county in South East England. The county town is Aylesbury, the largest town in the ceremonial county is Milton Keynes and largest town in the non-metropolitan county is High Wycombe....

), the Greenstead Roundabout in Colchester
Colchester
Colchester is an historic town and the largest settlement within the borough of Colchester in Essex, England.At the time of the census in 2001, it had a population of 104,390. However, the population is rapidly increasing, and has been named as one of Britain's fastest growing towns. As the...

 (Essex
Essex
Essex is a ceremonial and non-metropolitan county in the East region of England, and one of the home counties. It is located to the northeast of Greater London. It borders with Cambridgeshire and Suffolk to the north, Hertfordshire to the west, Kent to the South and London to the south west...

), the Sadlers Farm Roundabout in Benfleet (Essex) which is the junction between the A130
A130 road
The A130 is a major road in England linking Little Waltham, near Chelmsford, the county town of Essex, with Canvey Island in the south of that county. It is a primary route for most of its length, only losing that status south of the A13 junction at Sadlers Farm "magic" roundabout as it nears its...

, the A13 and the B1464 (although this is currently being converted to a signal-controlled roundabout, with work expected to be completed by early 2012), "The Egg
The Egg (roundabout)
The Egg is a magic roundabout in Tamworth, Staffordshire. The Egg forms the junction of the A51, A453 and A513 and terminates the B5000. It consists of the roads Ankerdrive and Bolebridge Street, and is listed as being part of the A51. The Egg has a cinema complex and restaurant in the centre, and...

" in Tamworth
Tamworth
Tamworth is a town and local government district in Staffordshire, England, located north-east of Birmingham city centre and north-west of London. The town takes its name from the River Tame, which flows through the town, as does the River Anker...

 (Staffordshire
Staffordshire
Staffordshire is a landlocked county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. Part of the National Forest lies within its borders...

) and the Hatton Cross Roundabout in London. Magic roundabouts are also known as "Ring Junctions"

Roundabouts with trams

Tram roundabouts are found in many countries.

In inner Melbourne
Melbourne
Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...

, particularly in the inner suburban area of South Melbourne
South Melbourne, Victoria
South Melbourne is an inner city suburb in Melbourne, Victoria, Australia, 2 km south from Melbourne's central business district. Its Local Government Area are the Cities of Port Phillip and Melbourne...

, where the tram network
Trams in Melbourne
The Melbourne tramway network is a major form of public transport in Melbourne, the capital city of the state of Victoria, Australia. , the network consisted of of track, 487 trams, 28 routes, and 1,773 tram stops. It was therefore the largest urban tramway network in the world, ahead of the...

 is extensive, tram tracks always pass through the central island of these roundabouts, with drivers required to give way, not only to vehicles coming towards them from their right, but also to trams coming at them from right-angles.

Having trams pass through small roundabouts is not a problem; through larger roundabouts it can be difficult, particularly when there is a junction between tram lines as well. In these cases, the roundabouts are very large, and often have tram stops in the middle. The Haymarket roundabout
Haymarket roundabout
Haymarket roundabout, informally known as the roundabout of death, is a notorious roundabout in inner-city Melbourne, Australia. The roundabout is formed at the junction of Peel St, Royal Parade, Elizabeth St, and Flemington Rd, on the northwest border of Melbourne's CBD. Two or three lanes of...

 between Royal Parade and Elizabeth Street
Elizabeth Street, Melbourne
Elizabeth Street is one of the main north-south streets in the central business district of Melbourne, Australia, part of the Hoddle Grid laid out in 1837.- Geography :...

 is the most notorious junction of this nature, containing a tram-stop, pedestrian crossings, three entering tram lines, traffic signals to stop vehicular traffic at each crossing point when a tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...

 is due, service roads and pedestrian crossing
Pedestrian crossing
A pedestrian crossing or crosswalk is a designated point on a road at which some means are employed to assist pedestrians wishing to cross. They are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely across the flow of vehicular traffic...

.

In Brussels
Brussels
Brussels , officially the Brussels Region or Brussels-Capital Region , is the capital of Belgium and the de facto capital of the European Union...

, Belgium, trams treat roundabouts in various ways: at the Barrière de St-Gilles
Saint-Gilles, Belgium
Saint-Gilles or Sint-Gillis is one of the nineteen municipalities located in the Brussels-Capital Region of Belgium.Saint-Gilles has a multicultural identity stemming from its diverse population...

/Bareel St-Gillis, the tram tracks form a circle in the carriageway, while Verboekhoven and Altitude Cent/Hoogte Honderd have reserved tram tracks on the inside of the roundabout. At Place Stéphanie/Stefaniaplein, they go straight through the middle, with a slip track up the Chaussée de Charleroi/Charleroisesteenweg.

In Dublin, Ireland, the Red Cow interchange at the N7/M50 junction is particularly infamous. It is a grade-separated motorway junction, and is signal-controlled with secondary lanes (separate from the main roundabout) for those making left turns. The junction, the busiest in Ireland, had tram lines added to it with the opening of the Luas
Luas
Luas , also promoted in the development stage as the Dublin Light Rail System, is a tram or light rail system serving Dublin, the first such system in the decades since the closure of the last of the Dublin tramways. In 2007, the system carried 28.4 million passengers, a growth of 10% since...

 system in 2004. The tracks pass across one carriageway of the N7, and across the southern M50 sliproads. Trams pass at a frequency of every 5 minutes at rush hour. The roundabout has been replaced with grade separated free flowing junction.

In Gothenburg
Gothenburg
Gothenburg is the second-largest city in Sweden and the fifth-largest in the Nordic countries. Situated on the west coast of Sweden, the city proper has a population of 519,399, with 549,839 in the urban area and total of 937,015 inhabitants in the metropolitan area...

, Sweden the roundabout and tram
Gothenburg tram
The Gothenburg tram network is part of the public transport system organised by Göteborgs Spårvägar AB, controlled by Västtrafik in the Swedish city of Gothenburg...

 stop at Korsvägen (the Crossroad) is of this type, and is rather infamous in the city. It is heavily trafficked by cars, and about one tram or bus per minute passes in several directions. This is further complicated by separated rights-of-way for trams and buses and the fact that it is also one of the busiest interchanges in the city. Another one is located at Mariaplan in the inner suburb of Majorna. The trams makes a right turn, giving the roundabout an odd design. Since traffic isn't heavy, this normally doesn't create any problems.

In Warsaw
Warsaw
Warsaw is the capital and largest city of Poland. It is located on the Vistula River, roughly from the Baltic Sea and from the Carpathian Mountains. Its population in 2010 was estimated at 1,716,855 residents with a greater metropolitan area of 2,631,902 residents, making Warsaw the 10th most...

, trams typically cross straight through roundabouts, and have junctions in the middle of them. In Wrocław, Poland, trams pass through the Powstańców Śląskich Roundabout, having a stop in the roundabout (north-headed track).

In Vítězné náměstí (Victory Square) in Prague
Prague
Prague is the capital and largest city of the Czech Republic. Situated in the north-west of the country on the Vltava river, the city is home to about 1.3 million people, while its metropolitan area is estimated to have a population of over 2.3 million...

, Czech Republic, a tramway crosses the carriage way of the roundabout at 3 places since 1942. Entering as well as leaving trams have to give way to all cars. In years 1932–1942 trams went around much like cars.

In Kiev
Kiev
Kiev or Kyiv is the capital and the largest city of Ukraine, located in the north central part of the country on the Dnieper River. The population as of the 2001 census was 2,611,300. However, higher numbers have been cited in the press....

, Ukraine
Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...

 an interchange of two "fast tram
Kiev tram
The Kiev Tramway is a tram network which serves the Ukrainian capital Kiev. The system was the first electric tramway in the former Russian Empire and the third one in Europe after the Berlin Straßenbahn and the Budapest tramway. The system currently consists of 139.9 km of track, including...

" lines is done below a roundabout.

Oslo
Oslo
Oslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...

, Norway also has many roundabouts with tram tracks passing through; for example at Bislett, Frogner plass, Sinsen
Sinsen
Sinsen is a mixed residential and commercial area in Grünerløkka borough of Oslo, Norway. The westernmost part of Sinsen is part of the borough Nordre Aker....

, Solli plass, Carl Berners plass and Storo.

In Wolverhampton
Wolverhampton
Wolverhampton is a city and metropolitan borough in the West Midlands, England. For Eurostat purposes Walsall and Wolverhampton is a NUTS 3 region and is one of five boroughs or unitary districts that comprise the "West Midlands" NUTS 2 region...

, England, the Midland Metro
Midland Metro
The Midland Metro is a light-rail or tram line in the West Midlands of England between the cities of Birmingham and Wolverhampton via West Bromwich and Wednesbury. It is owned and promoted by Centro, and operated by West Midlands Travel Limited, a subsidiary of the National Express Group , under...

 tram passes through the centre of a roundabout on approach to its terminus at St Georges. This also happens in New Addington
New Addington
New Addington is an area on the edge of South London in the London Borough of Croydon. It is a large local authority estate surrounded by open countryside, woodland and golf courses. The Prime Meridian crosses the eastern edge of New Addington...

 on the Tramlink
Tramlink
Tramlink is a tramway system in south London in the United Kingdom which began operation in May 2000...

 on Old Lodge Lane at the junction to King Henry's Drive.

In Salt Lake City, Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

 a light rail
Light rail
Light rail or light rail transit is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than traditional street-running tram systems...

 line on the south side of the University of Utah
University of Utah
The University of Utah, also known as the U or the U of U, is a public, coeducational research university in Salt Lake City, Utah, United States. The university was established in 1850 as the University of Deseret by the General Assembly of the provisional State of Deseret, making it Utah's oldest...

 crosses a roundabout where Guardsman Way meets South Campus Drive. Like virtually all rail crossings in the United States, both crossings in the circle are equipped with boom barrier
Boom barrier
A boom barrier is a bar, or pole pivoted in such a way as to allow the boom to block vehicular access through a controlled point. Typically the tip of a boom gate rises in a vertical arc to a near vertical position. Boom gates are often counterweighted, so the pole is easily tipped...

s.

In Kassel
Kassel
Kassel is a town located on the Fulda River in northern Hesse, Germany. It is the administrative seat of the Kassel Regierungsbezirk and the Kreis of the same name and has approximately 195,000 inhabitants.- History :...

, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, the tram line serving Lines 4 and 8 passes through the middle of the roundabout at Platz der Deutschen Einheit. The tram stops are in the middle of the roundabout. To allow trams through, traffic is controlled by lights on the roundabout. Pedestrian access is via subway and street level crossings at the traffic lights for the trams.

Roundabouts with railways

In Jensen Beach, Florida
Jensen Beach, Florida
Jensen Beach is a census-designated place in Martin County, Florida, United States. The population was 11,100 at the 2000 census. It is part of the Port St...

, the main line of the Florida East Coast Railway
Florida East Coast Railway
The Florida East Coast Railway is a Class II railroad operating in the U.S. state of Florida; in the past, it has been a Class I railroad.Built primarily in the last quarter of the 19th century and the first decade of the 20th century, the FEC was a project of Standard Oil principal Henry Morrison...

 running north-south bisects the two-lane roundabout at the junction of Jensen Beach Boulevard running east-west and three other roads and the service entrance to a large shopping plaza. Boom barriers are in place at the railway crossings. The landscaped centre island bisected by the tracks was originally curbed
Curb (road)
A curb, or kerb , is the edge where a raised pavement/sidewalk/footpath, road median, or road shoulder meets an unraised street or other roadway.-Function:...

, but 18-wheelers
Semi-trailer truck
A semi-trailer truck, also known as a semi, tractor-trailer, or articulated truck or articulated lorry, is an articulated vehicle consisting of a towing engine , and a semi-trailer A semi-trailer truck, also known as a semi, tractor-trailer, or (in the United Kingdom and Ireland) articulated truck...

 had trouble negotiating the roundabout, so the curbs were replaced with painted drive over concrete strips. A proposed fountain in the centre island has never been built. The roundabout was built in the early 2000s and has improved traffic flow considerably although there are still delays caused by the many long freight trains coming through.

Two roundabouts in the Melbourne metropolitan area, Highett, Victoria
Highett, Victoria
Highett is a suburb in Melbourne, Victoria, Australia, 16 km south-east from Melbourne's central business district and 2 km east of Port Phillip Bay. Its Local Government Area is the City of Bayside and the City of Kingston...

 and Brighton
Brighton, Victoria
Brighton is a suburb of Melbourne, Victoria, Australia, 11 km south-east from Melbourne's central business district. Its Local Government Area is the City of Bayside. At the 2006 Census, Brighton had a population of 20,651...

, have heavy rail crossing the roundabout and through the inner circle. Boom barriers protect the rail from oncoming traffic at the appropriate points in the roundabout.

At the Driescher Kreisel in Bergisch Gladbach
Bergisch Gladbach
' is a city in the Cologne/Bonn Region of North Rhine-Westphalia, Germany and capital of the Rheinisch-Bergischer Kreis .-Geography:Bergisch Gladbach is located east of the river Rhine, approx...

, Germany, a railway serving a nearby paper factory crosses a roundabout, which is located next to a shopping centre and pedestrian zone. The flow of traffic and pedestrians is governed by 14 barriers, 22 traffic lights and 8 loudspeakers. The barriers are closed three times a day for 7 minutes to allow trains to pass.

Hamburger roundabout/throughabout/cut-through roundabout

These resemble a normal roundabout but are signalised
Traffic light
Traffic lights, which may also be known as stoplights, traffic lamps, traffic signals, signal lights, robots or semaphore, are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic...

 and have a straight-through section of carriageway for one of the major routes. The hamburger name derives from the fact that the plan view resembles the cross-section through a hamburger
Hamburger
A hamburger is a sandwich consisting of a cooked patty of ground meat usually placed inside a sliced bread roll...

. There are examples on the A580 East Lancashire Road in St Helens
St Helens, Merseyside
St Helens is a large town in Merseyside, England. It is the largest settlement and administrative centre of the Metropolitan Borough of St Helens with a population of just over 100,000, part of an urban area with a total population of 176,843 at the time of the 2001 Census...

, England, on Haydock Island in Merseyside (which also features the M6 passing overhead), and on the Astley/Boothstown border near to Manchester. More examples are the A6003 at Kettering
Kettering
Kettering is a market town in the Borough of Kettering, Northamptonshire, England. It is situated about from London. Kettering is mainly situated on the west side of the River Ise, a tributary of the River Nene which meets at Wellingborough...

, the A538 near Manchester Airport, the "Showcase" junction on A329 at Winnersh, Berkshire. and the A63/A1079 Mytongate junction in Hull. Examples also exist in Bracknell
Bracknell
Bracknell is a town and civil parish in the Borough of Bracknell Forest in Berkshire, England. It lies to the south-east of Reading, southwest of Windsor and west of central London...

, Hull
Kingston upon Hull
Kingston upon Hull , usually referred to as Hull, is a city and unitary authority area in the ceremonial county of the East Riding of Yorkshire, England. It stands on the River Hull at its junction with the Humber estuary, 25 miles inland from the North Sea. Hull has a resident population of...

, Nottingham
Nottingham
Nottingham is a city and unitary authority in the East Midlands of England. It is located in the ceremonial county of Nottinghamshire and represents one of eight members of the English Core Cities Group...

 and Reading
Reading, Berkshire
Reading is a large town and unitary authority area in England. It is located in the Thames Valley at the confluence of the River Thames and River Kennet, and on both the Great Western Main Line railway and the M4 motorway, some west of London....

 (all in England), as well as on the N2/M50
M50 motorway (Ireland)
The M50 motorway is a motorway in Ireland running in a C-shaped ring around the north-eastern, northern, western and southern sides of the capital city, Dublin. The northern end of the route is located at the entrance to the Dublin Port Tunnel. Anti-clockwise it heads northwest through the tunnel...

 intersection in Dublin, Ireland.

A more advanced and safer version of a hamburger roundabout is a roundabout interchange
Roundabout interchange
A roundabout interchange is a type of interchange between a controlled access highway such as a motorway or freeway, and a minor road, in which the slip roads to and from the motorway carriageways converge at a single roundabout, which is grade-separated from the motorway lanes with bridges...

, separating the straight roadway and using underpasses or overpasses to cross the roundabout itself.

External links

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