|
|
|
|
Roundabout
|
| |
|
| |
A roundabout is a type of road junction at which traffic enters a one-way stream around a central island. In the United States it is commonly known as a "rotary" or a "traffic circle", but sometimes is technically called a modern roundabout, in order to emphasize the distinction from the older, very much larger type of traffic circle which usually had poor or no visibility across the central island.
In countries where people drive on the right, the traffic flow around the central island of a roundabout is counterclockwise.
Discussion
Ask a question about 'Roundabout' Start a new discussion about 'Roundabout' Answer questions from other users |
Encyclopedia
A roundabout is a type of road junction at which traffic enters a one-way stream around a central island. In the United States it is commonly known as a "rotary" or a "traffic circle", but sometimes is technically called a modern roundabout, in order to emphasize the distinction from the older, very much larger type of traffic circle which usually had poor or no visibility across the central island.
In countries where people drive on the right, the traffic flow around the central island of a roundabout is counterclockwise. In countries where people drive on the left, the traffic flow is clockwise.
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 motorways, highways, or similar fast roads.
Difference from traffic circles and rotaries
Roundabouts are sometimes referred to as "traffic circles" or "rotaries", but a technical distinction was made in some jurisdictions between roundabouts, traffic circles, and rotaries 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.
In technical usage, circular intersections that have the following characteristics are roundabouts, and those that do not are traffic circles or rotaries:
- Entering vehicles yield ("give way") to vehicles in the roundabout; i.e: vehicles inside the circle have the right of way. This is opposite of the traffic circle.
- Deflection is used to maintain low speed operation. Drivers must maneuver (are deflected) around the splitter islands and central island, at speeds of 15-25 mph (24-40 km/h). Many older traffic circles allow speeds as high as 45 mph (72 km/h) due to insufficient deflection.
- Parking is prohibited on the circulatory roadway
- Pedestrians are (usually) prohibited from the central island
- All vehicles circulate around the central island in the same direction, and this direction is decided 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 counterclockwise.
The term traffic circle is not used in United Kingdom. Most circular intersections there meet the criteria for roundabouts. The U.K. does, however have roundabout variants such as mini-roundabouts and magic-roundabouts — see below).
In U.S. usage, many laypersons use roundabout, traffic circle, and rotary interchangeably. Many old rotaries and traffic circles remain in the Northeastern United States. Since many of the older ones have unfavorable safety records, transportation professionals are careful to use "roundabout" when referring to newer designs and "traffic circle" when referring to ones that do not meet the criteria listed above.
A large number of traffic circles have been converted to signalized intersections and interchanges. Several have been converted to roundabouts meeting modern design standards, including the Kingston traffic Circle in New York and several in New Jersey.
Seattle, Washington has well over 100 roundabouts that have been built over the last two decades, with many more located throughout the Seattle Metropolitan area. In addition, hundreds of mini-roundabouts have long existed in the city's residential neighbourhoods.
History
The first roundabout was constructed in Paris around the Arc de Triomphe in 1901. According to the BBC the first "recognizable modern roundabout" was New York's Columbus Circle. The first British roundabout was five years later, in Letchworth Garden City in 1909 - originally intended partly as a traffic island for pedestrians. However, the widespread use of roundabouts began when British engineers re-engineered the traffic circle in the mid-1960s and Frank Blackmore invented the mini roundabout 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 junctions that have traffic lights. 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 islands and therefore encourage slower and safer speeds (see traffic calming).
Safety
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 underpasses.
At intersections 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.
Cyclists do not get the same safety benefits from roundabouts as vehicle drivers. An analysis of the national crash database 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. Cyclists are two to three times as likely to be in a crash at a multi-lane roundabout than at a traffic signal. New Zealand researchers have proposed a design that will reduce the speed differential between cyclists and motorists to improve cyclists' safety.
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. This is because, unlike traffic signals, it is hard to hear if there is an adequate gap in traffic 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 yielded to the pedestrian.
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. Engineers point out that since vehicle speeds are slower, should a driver fail to yield at a roundabout the risk and severity of pedestrian crashes are lower than if the same driver had run a red light. However, the blind community considers this to be a civil rights issue, not an engineering issue. While pedestrian crossings with traffic lights installed in roundabouts are not unheard of (see below), and would reduce the possibility that a blind pedestrian might be run over by vehicles failing to yield, they would also substantially increase the cost of roundabout construction and maintenance (essentially, both types of intersections being built at every intersection). 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 intersections.
Capacity
Like any at-grade intersection, roundabouts do not cope well with the very heavy traffic on primary motorways or freeways, leading to long queues. Britain's strategic road network has some isolated roundabouts on otherwise almost motorway-like roads (for example, A1/A421 and Broxden Junction) 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".
A particular cause of congestion at a roundabout is when many motorists want to make a turn that effectively crosses oncoming traffic. The two images to the right, which presume right-hand traffic, show how opposing drivers making left turns will get into each other's path twice in a roundabout, but in most countries they will not cross paths at a conventional intersection. While always a potential issue, periods of low traffic density typically result in both drivers making simple adjustments to avoid each other and then going on their way. When traffic density crosses a certain threshold however, adjustments to speed and direction are no longer simple, and may not even be possible without circling the roundabout a second time, or even several times, in order to get a proper opening. And often, impatience overrules any inclination for said driver[s] to do other than "go forward".
On the other hand, traffic signals often suffer from inefficient operation at intersections, especially those with heavy side road traffic, or high proportions of turns across oncoming traffic. Long waits at traffic lights can and do exist, regardless of traffic volume. At locations with low to medium traffic volumes, roundabouts work well under these conditions. Roundabouts actually work best when approaching volume on all legs is roughly equal (although it would be a mistake to assume that a roundabout would not work if volumes are not equal), yet roundabouts also substantially reduce delays in off-peak periods. Consider that, even during off-peak travel, traffic on one street must always stop and wait at a signal for the phase to change, even if there is no conflicting traffic. This is not the case at a roundabout — when there is low-to-no conflicting traffic in a roundabout, all vehicles safely keep moving.
Several software packages exist to help with calculating Capacity and Queues at roundabouts. These include ARCADY, RODEL and aaSIDRA.
Types
Large roundabouts such as those used at motorway intersections typically have two to four lanes around the central hub, and may 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, while 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, Hull, Nottingham and Reading (all in England), as well as on the N2/M50 intersection in Dublin, Ireland.
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; in fact, they are more like traffic circles.
Mini roundabouts
Mini-roundabouts exist at smaller intersections to avoid the use of signals, stop signs or the necessity to yield in favour 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 terms of right of way. They can often come in "chains", making navigation of otherwise awkward junctions easier. There are usually different road signs used to distinguish mini roundabouts from larger ones.
Mini-roundabouts are also common in Irapuato, Mexico, usually marked with a tiny grassy circle enclosed edge paving, 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 centre surrounded by a sloped "overrun area" of a different colour from the roadway and up to a metre in thickness 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). These are not well suited for bus routes, as mounting the apron can be somewhat uncomfortable to passengers.
In the UK 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. (In practice, few motorists obey these rules). Some local authorities have installed double white 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 Roundabouts
These roundabouts do not form a complete circle and are in a "raindrop" shape. They are appearing at U.S. 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, a complete circle is unnecessary. 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.
Also known in the UK as a dumbell roundabout.
Turbo roundabouts
In the Netherlands, a relatively new type of roundabout is built increasingly often. It provides a forced spiraling 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 traveling 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 are typically built with raised lane separators. Cheaper implementations with only road markings exist, but hurt the efficiency (regarding safety, speed, and capacity) of the design by enabling users to cheat the system.
Roundabouts on motorways
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 ramps. 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.
In Northern Ireland 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.
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, M8/M73 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 applies. The large diameter 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 freeway in the United States, also has two large at-grade roundabouts (or rotaries as they are called in that state) in Gloucester, Massachusetts. 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 freeway linking Cape Cod to Boston; directly opposite is another freeway, 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 Route 3 and US 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 freeway 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.
In the Netherlands, A6 motorway and A7 motorway cross near Joure using a roundabout. For the intersection between the A200 and the A9 a 3-level stacked roundabout is used. Near Eindhoven (the Leenderheide junction), the intersection for the A2 is done with a roundabout. An overpass is built for the A67 from Antwerp to Germany.
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 counterclockwise 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 in Hemel Hempstead (Hertfordshire), which has six intersections; but also in High Wycombe (Buckinghamshire), the Denham Roundabout in Denham (Buckinghamshire), the Greenstead Roundabout in Colchester (Essex), the Sadler's Farm Roundabout in Benfleet (Essex) which is the intersection between the A130, the A13 and the B1464. "The Egg" in Tamworth (Staffordshire) and the Hatton Cross Roundabout in London . Magic roundabouts are also known as "Ring Junctions", while larger ones are sometimes known as "Gyratories".
Roundabouts with trams
Tram roundabouts are 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, 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 between Royal Parade and Elizabeth Street 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, Belgium, 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 Zagreb, Croatia, the Novi Zagreb district houses two infamous roundabouts (Western Rotary and Eastern Rotary), of which two tram lines pass under the western one (a third line is also planned, which will utilize the western leg of the roundabout), and the eastern one is actually a complex multi-level interchange with a tram roundabout in the middle and tram tracks intersecting the roundabout at one point.
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 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 tram 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 Wroclaw, Poland, trams pass through the Powstanców Slaskich Roundabout, having a stop in the roundabout (north-headed track).
In Vítezné námestí (Victory Square) in Prague, 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, 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, England, 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 Tramlink on Old Lodge Lane at the junction to King Henry's Drive.
An underpass in Sheffield, England allows the tram to travel below a major roundabout, avoiding what would otherwise be a serious hindrance to traffic. A second notable tram/roundabout feature on the Sheffield system has three main branches meet and junction together atop a large, earth-worked traffic island with each line being bridged across to the outside of the feature high above the traffic, along with a couple of pre-existing walkway bridges that are now complemented by the pedestrian paths set alongside two of the incident lines.
In Salt Lake City, Utah a light rail line on the south side of the University of Utah 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 barriers.
Roundabouts with railways
In Jensen Beach, Florida, the main line of the Florida East Coast Railway running north-south bisects the two-lane roundabout at the intersection 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, but
18-wheelers 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.
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 hamburger. There are two such examples on the A580 East Lancashire Road in St Helens, England, one at (which also features the M6 passing overhead), the second is on the . More examples are the A6003 at Kettering and the A538 near Manchester Airport . Yet another can be seen at the junction of in Perth, WA, Australia. An example of such an intersection in the United States can be found on the in Everett, Massachusetts.
A more advanced and safer version of a hamburger roundabout is a roundabout interchange, separating the straight roadway and using underpasses or overpasses to cross the roundabout itself.
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 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) 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 pedestrians 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 vans, 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 favour.
Marked perimeter cycle lanes
An early attempt to deal with the problem was to mark preferential lanes for cyclists. 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 coloured road surface and edge lines of the cycle lanes indicate that motorists 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 motorists as well as cyclists below that of conventional intersections. 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 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. A roundabout with 2 lanes should place the crosswalk two car lengths from the intersection.
See the United States DOT publication, .
Advantages of roundabouts
- Roundabouts are safer than signal controlled intersections, with accidents usually occuring at a slower speed and at a slight angle instead of a T-bone or rear end collision at intersections.
- Most roundabouts are not controlled by traffic lights. This reduces waiting time, compared to crossroads that have traffic lights.
- Roundabouts allow u-turns, which are often impossible or forbidden in normal road junctions.
Disadvantages of roundabouts
- Roundabouts require maneuvering within a short distance, which is difficult especially in roundabouts that have several lanes and during heavy traffic.
- A roundabout occupies more space than crossroads, and the space in the middle cannot be used.
- Unfamiliar and elderly drivers tend to get lost and use roundabouts improperly.
Examples of roundabouts
- Monument Circle, Indianapolis
- Elephant and Castle, London
- The Plain, Oxford
- St George's Circus, London
- Place Charles de Gaulle (Place de l'Étoile), Paris — 12 roads regularly spaced at 30° intervals around the Arc de Triomphe
- Los Alamitos Traffic Circle, Long Beach, California
- Glorieta de Bilbao, Madrid — a star shaped roundabout
- Columna de la Independencia Rondabout in Paseo de la Reforma, Mexico City
- clock tower roundabout,Dubai,United Arab Emirates(UAE).
- Trade Center roundabout,Dubai,United Arab Emirates (UAE)
Miscellany
*The Kinsale Road Roundabout in Cork, Ireland is a very large and irregularly shaped, three lane, signal controlled roundabout. The roundabout is situated on the N25 southern ring road dual carriageway, at the intersection with a dual-carriageway to the city centre, a road to Bishopstown, and the airport or Kinsale road. With the huge traffic volumes at the intersection, the dangerous and difficult navigation of the roundabout had given rise to the "Magic Roundabout" nickname and at times traffic jams of a kilometre in length were not uncommon, especially during peak periods. However this roundabout has been upgraded to a grade-separated junction where the N25 now passes over it.
- East Longmeadow, MA contains a central rotary where 7 roads come together into a roundabout. The town has talked about changing its design to the dismay of some residents who would like it kept. It is listed in Ripley's Believe It or Not.(
- The roundabout at the junction of Tyndall Street and Ocean Way in Cardiff, Wales, has cubes and other geometric shapes constructed from road signs and is known locally as "The Magic Roundabout".
- Crawley, West Sussex, England, has a large rectangular roundabout which contains a hotel in the centre, giving rise to the address, "The Squareabout, Crawley".
- Mooroolbark, Melbourne contains a triple-roundabout , that is, three consecutive roundabouts, on Hull Rd. They were built to replace a dangerous area where three secondary roads joined Hull Rd at separate places within 200 m. Each roundabout allows drivers to turn onto or off from one of the three secondary roads.
- Two roundabouts in the Melbourne metropolitan area, Highett and Brighton , 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.
- St Kilda Junction, St Kilda, Melbourne, was once an uncontrolled seven-street roundabout also containing a tram junction in the middle; it was drastically altered in the 1970s to make it a two-level, light-patrolled intersection.
- One of the most famous landmarks in Guadalajara, Mexico is the Minerva Fountain Roundabout, which contains a huge fountain surrounding a statue of the Roman goddess Minerva. It is in the middle of a series of 3 consecutive roundabouts, located in the intersection of 5 avenues: López Mateos, Vallarta, López Cotilla, Agustín Yáñez and Golfo de Cortez. A long tunnel runs under all the three roundabouts.
- The Australian cities of Griffith in New South Wales, and Albany in Western Australia contain no traffic lights, only roundabouts.
- The town of Milton Keynes, England, is famous for having grid roads which have roundabouts at almost every intersection, Like Canterbury and Stevenage, England which is known for its abundance of roundabouts, mini-bouts on most roads.
- The Shepherd and Flock roundabout in Farnham, Surrey, England, extends to over with 17 houses and a pub that lie within, making it one of the largest inhabited roundabouts in the UK. An oddity of 1960s road planning has left the 17 houses and the pub encircled by several lanes of tarmac that connects Guildford to Winchester (A31). The completed roundabout was therefore named after the pub "The Shepherd and Flock".
- Roosevelt Circle, an interchange on Interstate 93 in Medford, Massachusetts is a roundabout constructed over the highway as a pair of curved overpasses.
- A roundabout dog is a home-made street installation placed in roundabouts, a phenomenon that occurred all over Sweden in 2006.
- The city of Chandigarh, India, by Le Corbusier, uses roundabouts at each junction of the V2/V3 roads surrounding the sector grids.
See also
External links
- by the U.S. Federal Highway Administration, FHWA-RD-00-67, June 2000 (or see the [https://www.nysdot.gov/portal/page/portal/main/roundabouts/files/00-067.pdf entire pdf] in one file)
- from the U.S. Manual on Uniform Traffic Control Devices
- [https://www.nysdot.gov/portal/page/portal/main/roundabouts/files/eiupdate.pdf Roundabouts: Interim Requirements and Guidance] by the New York State Department of Transportation, June 20, 2000
- and related and
- Traffic Congestion in City Streets: one suggestion for relief takes the form of a novel safety island, Popular Science monthly, February 1919, page 69, Scanned by Google Books: http://books.google.com/books?id=7igDAAAAMBAJ&pg=PA69 Category:Articles with citations to Popular Science archive Category:Articles with verifiable citations via Google Books
|
| |
|
|
