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A roundabout or '''rotary''' is a type of Road Junction (or Traffic Calming device) at which Traffic enters a stream around a central island after first yielding (giving way) to the circulating traffic. In the United States it is technically called a "'''modern roundabout'''", to emphasize the distinction from the older, larger type of Traffic Circle (though some Americans still refer to modern roundabouts as '''"Traffic Circles"'''). In many parts of the English Midlands roundabouts are commonly referred to as "islands". Overall, roundabouts are statistically safer than both traffic circles and traditional intersections, with the exception that cyclists have a significantly increased crash rate at large roundabouts. Roundabouts do not cope as well with the traffic on Motorway s, Highway s, or similar fast roads. DIFFERENCE BETWEEN ROUNDABOUTS AND TRAFFIC CIRCLES Roundabouts are sometimes referred to as "traffic Circles" , but a technical distinction was made in some jurisdictions between roundabouts and traffic circles in the mid- 1960s . Starting in that decade, research in the United Kingdom found that circular intersections with certain geometric characteristics and traffic control schemes tended to be safer than those without them. The key differences are: In the United Kingdom the term 'traffic circle' is not used, and all types are known as roundabouts (but see Mini-roundabouts and Magic Roundabouts below). In the United States , circular intersections that meet the design standards shown in the table above are termed "modern roundabouts," to distinguish them from older rotaries or traffic circles. In Massachusetts , rotaries are nearly always built to the standards of a British roundabout, and a "roundabout" refers to an especially small rotary with crosswalks, between high-traffic roads.Commmonwealth of Massachusetts Driver's Manual {Link without Title} HISTORY AND SAFETY .]] The first modern roundabout was constructed in Paris around the Arc De Triomphe in 1901 , closely followed by Columbus Circle in New York City in 1904. The first British roundabout was five years later, in Letchworth Garden City in 1909 - originally intended partly as a traffic island for pedestrians1. However, the widespread use of roundabouts began when British engineers re-engineered the traffic circle in the mid- 1960s to overcome its limitations of capacity and for safety issues. Unlike traffic circles, roundabouts operate with yield control to give priority to circulating Traffic and eliminate much of the driver confusion associated with traffic circles and driver wait associated with Junction s that have Traffic Light s. Roughly the same size as signalled intersections with the same capacity, roundabouts also are significantly smaller in diameter than traffic circles, separate incoming and outgoing traffic with Pedestrian Island s and therefore encourage slower and safer speeds (see Traffic Calming ). Roundabouts are safer than both traffic circles and traditional intersections—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 , compared with the intersections they replaced). Roundabouts also reduce points of conflict between pedestrians and motor vehicles and are therefore considered to be safer for them. However, roundabouts, especially large fast moving ones, are unpopular with some cyclists. This problem is sometimes handled on larger roundabouts by taking foot and bicycle traffic through a series of Underpass es. In addition to improved vehicle and pedestrian safety, and in spite of lower speeds, roundabouts dramatically outperform traffic circles in terms of vehicle throughput and, because a roundabout's circular traffic is always moving, they outperform ordinary junctions with traffic signals as well. Multi-lane and large roundabouts can be hazardous for cyclists. An analysis of the national crash database {Link without Title} in New Zealand 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 intersections. The most common roundabout crash type for cyclists involves a motor vehicle entering the roundabout and colliding with a cyclist who is already 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 roundabout carriageway. Designs that have Marked Perimeter Cycle Lanes are found by research data to be even less safe than those without them. If the adjacent cross-walks are not properly designed, there are increased risks for persons with visual impairments, because of the speed at which traffic exits the roundabout. This issue has led to a conflict in the United States between the visually impaired and Civil Engineering communities; the visually impaired have taken the position that roundabouts (rather than signal-controlled crossings) are acceptable only if there are pedestrian crossings with lights at ''each'' road connecting to a roundabout. Although such crossings would reduce the possibility that a Blind pedestrian might be run over by vehicles entering or exiting the roundabout at unsafe speeds, they would also increase the cost of a roundabout and decrease its throughput. , England . The traffic drives on the left.]] In addition, roundabouts do not cope well with the traffic on motorways or similar roads, leading to long queues. Britain's strategic road network has many isolated roundabouts on otherwise almost motorway-like roads (for example, A1/A421) and even on a few motorways (for example, the A601(M) , A627(M) , and M271 have roundabouts on the main line). Some of these roundabouts, as well as other busy roundabouts, have had traffic lights added and are termed "signal controlled roundabouts". Roundabouts are not suitable for junctions where the exits suffer from Traffic Congestion . Congestion on one exit commonly blocks a roundabout and spreads to all entering directions. The roundabout of Kwai Tsing Interchange in Hong Kong was replaced by a large Box Junction with Traffic Light s after recurring area traffic congestion when numerous container trucks journeyed to Kwai Chung Container Port after a Typhoon . TYPES OF ROUNDABOUT Large roundabouts such as those used at motorway intersections typically have two to four lanes around the central hub, and frequently have traffic lights regulating flow during peak hours. 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. Another type of roundabout is the through-about roundabout or "hamburger" junction. This type of roundabout enables straight-through traffic on one road to cross over the central island, whilst all other traffic must drive around the island. As a consequence this junction must always be controlled by traffic lights. Examples of this type exist in Bracknell , Nottingham and Reading , as well as on the N2 / M50 intersection in Dublin , Ireland . Gyratory system The term "gyratory" (for example, the Hanger Lane Gyratory System ) is sometimes used in England when a roundabout is large and has non-standard lane markings or priorities; in fact, they are more like traffic circleshttp://www.alaskaroundabouts.com/history.html. Mini roundabouts Mini-roundabouts exist at smaller intersections to avoid the use of signals, stop signs or the necessity to yield in favor of one road of traffic. Mini-roundabouts can be a painted circle, a low dome, or often are small garden beds. 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 term of right of way. They can often come in "chains", making navigation of otherwise awkward junctions easier. There are usually different Road Sign s used to distinguish mini roundabouts from larger ones. Mini-roundabouts are also common in Irapuato, Mexico , usually marked with a tiny grassy circle enclosed with sidewalk edges, and in Calgary, Canada 's inner-city Mount Royal and Rosedale neighbourhoods, where mini-roundabouts recently replaced intersections formerly controlled by stop signs to combat increasing cut-through traffic. A slightly larger version of a mini-roundabout, sometimes called a "small roundabout", is designed with a raised center surrounded by a sloped "overrun area" of a different color from the roadway and up to a meter in thickness called a "truck apron". The truck apron's design discourages small vehicles from shortcutting over it while at the same time allowing the mini-roundabout to more easily accommodate the turning radius of larger vehicles. In the U.K the maximum diameter permissible of a mini-roundabout is 4m. Whilst it may be physically possible, it is illegal for vehicles like cars, which can turn around the mini-roundabout, to go over the painted island, or around the wrong way- vehicles should treat it like a solid island and proceed around it. Certain local authorities have installed double while lines around the island to indicate this, but these are not permissible. The centre island also must be able to be over-run by larger vehicles. If this is not possible, perhaps due to plants, or street furniture it is considered a small roundabout not a mini roundabout and as such must adhere to the stricter roundabout guidelines. Raindrop or peanut shaped roundabouts interchange in North Carolina .]] These roundabouts do not form a complete circle and are in a "raindrop" shape. They are appearing at Interstate interchanges to provide a free-flowing left turn to the on-ramps and eliminating the need for turn signals and lanes. Since the on and off-ramps are one-way, the need for a complete circle is not necessary. This means that drivers entering the roundabout from the bridge do not need to yield and prevents queuing on narrow, two-lane bridges. These roundabouts have been used at new interchanges so that a two-lane bridge can be built for less cost than a three-lane, as well as replacing traffic signals that are inefficient without a turning lane. Roundabouts on motorways See Also: Roundabout interchange While roundabouts do not usually interrupt motorways in the UK or Ireland, a common type of motorway intersection (suited only for lower volumes of traffic) consists of a Grade Separated roundabout above or below the main motorway, accessed via sliproads. Most intersections on Dublin 's M50 Motorway ring-road use this configuration — although several junctions have a greater volume of traffic than the capacity such roundabouts can accommodate. An additional improvement is the 3-level stacked roundabout — this is a roundabout interchange where ''both'' roads are grade separated. In the United Kingdom , the M25 / A3 and A1(M) / M18 interchanges are examples of this type. These junctions however have less capacity than a full Free-flow Interchange . A similar design to this is the Three-level Diamond interchange. The A52 motorway in Switzerland links with three sections of road near Hinwil heading toward Hinwil , Forch and Rapperswil . The intersection takes shape in the form of a massive roundabout on the motorway. However, the sign for a roundabout is not used and a speed limit of 80 km/h (50 mph) applies. The size of the roundabout conceals the fact that it is a roundabout at all. The A7 motorway, also in Switzerland, also has a motorway roundabout (at its terminus in Kreuzlingen ), but it is smaller in size. Massachusetts Route 128 , a motorway/ Freeway in the United States , also has two large At-grade roundabouts (or ''rotaries'' as they are called in that state) in the city of Gloucester . They are signed as Exits 10 and 11. Roundabouts in Massachusetts follow the same general rule as in the UK, with circling traffic receiving right of way. There also was a former roundabout at the southern terminus of Route 3 , a motorway linking Cape Cod to Boston ; directly opposite is another motorway, the start of the Mid-Cape Highway section of US 6 heading over the Sagamore Bridge . Due to the small size of the roundabout, and the fact that Routes 3 and 6 make up the shortest way to get between the Cape and Boston, traffic tie-ups and accidents were common, especially in the Summer months, when drivers from other states were often confused at how to navigate the roundabout. This roundabout was replaced with a standard motorway interchange during a three-year conversion project which concluded in 2007 . In the city of Malmö , Sweden , there is a roundabout connecting two motorways, "Autostradan" from Lund , and the "Inner ring road". It is signposted as a motorway through this roundabout. Today these two motorways are considered local, but before year 2000 they were part of the European roads E6 , E20 and E22 . Controlled roundabouts Some bridges on Beijing 's 2nd 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 roundabouts are common in Great Britain and Ireland , where they have been introduced in an attempt to alleviate traffic problems at over-capacity roundabout intersections or to prevent some flows of traffic dominating others (around the M50 in Dublin for example). "Magic" roundabouts The town of Swindon in Wiltshire , England is known for its " Magic Roundabout ". This roundabout is at an intersection 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 anti-clockwise 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 in Denham ( Buckinghamshire ), the Greenstead Roundabout in Colchester ( Essex ) and the Sadler's Farm Roundabout in Benfleet ( Essex ); " The Egg " in Tamworth , ( Staffordshire ); and the Hatton Cross Roundabout in London {Link without Title} . Magic roundabouts are also known as "Ring Junctions". Roundabouts with trams Most notably found in inner Melbourne , particularly in the inner suburban area of South Melbourne , where the Tram Network is extensive. Tram tracks always pass through the central island of these roundabouts. They can be worrying for inexperienced drivers, as they must 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 a small roundabouts is not a problem; through larger roundabouts it can be difficult, particularly when there is a tram junction (i.e. the tram may do more than simply pass straight through the intersection). In these cases, the roundabouts are very large, and often have tram stops in the middle. Flemington Junction is the most notorious intersection 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 is due, service roads and Pedestrian Crossing . There are a few larger roundabouts in Brussels where several tram routes converge from different directions, and the tram lines are laid around the roundabout allowing the trams to follow the same path as other traffic. In Dublin , Ireland , the Red Cow ("Mad Cow") Roundabout at the N7 / M50 intersection 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 hand turns. The junction, the busiest in Ireland, had tram lines added to it with the opening of the LUAS 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. In Gothenburg , Sweden the roundabout and Korsvägen Tram stop (the Crossroad) at the Trade Fair 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 Wrocław , Poland tram passes through Powstańców Śląskich Roundabout, having a stop in the roundabout (north-headed track). In Kiev , Ukraine an interchange of two " Fast Tram " lines is done below a roundabout. Oslo , Norway also has many roundabouts with Tram tracks passing through; for example at Bislett, Frogner plass, Sinsen , Solli plass and Storo. In Wolverhampton , UK , the Midland Metro tram passes through the centre of a roundabout on approach to its terminus at St Georges. This also happens in New Addington on the Croydon Tramlink on Old Lodge Lane at the junction to King Henry's Drive. An underpass in Sheffield , UK allows the tram to travel below a major roundabout, avoiding what would otherwise be a serious hindrance to traffic. Hamburger roundabout/throughabout/cut-through roundabout These resemble a normal roundabout but are signalised 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 . ROUNDABOUTS AND CYCLISTS Cycle facilities at roundabouts Research has shown that even in large circular intersections 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 '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 intersection has a marked bicycle lane or sidepath around its outside ''(see "Marked perimeter cycle lanes" below)''. The results of this study concerning circular intersections are summarized on a Web Site (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 ) in 1984. Collisions typically occur when a motorist is entering or leaving the circular roadway. A motorist entering the circular roadway must yield 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 s in a Crosswalk . 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 yield 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 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 intersections. Cycle lanes around the outside of circular intersections are therefore falling out of favor. Marked perimeter cycle lanes s on St John's roundabout in Newbury, Berkshire , England . This example is from a country where Traffic keeps to the left, and traffic in the circular Roadway of the roundabout travels Clockwise .]] An early attempt to deal with the problem was to mark preferential lanes for cyclists, as in the picture (right). With cycle lanes, Bicyclists 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 colored road surface and edge lines of the cycle lanes indicate that Motorist s are required to yield to bicyclists at all locations where their paths may cross. Modern design guidance The special features of modern roundabouts, including splitter/diverter islands and small diameter of the circular roadway, decrease the speed of motor traffic and so reduce the risk of collisions for bicyclists as well as motorists below that of conventional intersections. Design guidance for modern roundabouts recommends terminating cycle lanes well before the entrances, so bicyclists merge into the stream of motor traffic. Bicyclists who lack the skill and confidence to do this may use the crosswalks as pedestrians. Modern design guidance also recommends placing the crosswalks far enough from the roundabout so that at least one exiting vehicle can wait without blocking the circular roadway. See the Informational Guide . EXAMPLES OF ROUNDABOUTS
MISCELLANY cinema built in a roundabout]]
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