Roundabouts
A roundabout or rotary is a type of road junction
(or traffic calming device) at which traffic streams around
a central island, after first yielding (giving way) to
the circulating traffic. Roundabouts are statistically
safer than both traffic circles and traditional intersections,
though they do not cope as well with the traffic on motorways
or similar fast roads.
Perhaps the greatest roadway invention of all
time is the roundabout. Despite the tendency
of Americans to be afraid of them, roundabouts
were actually invented in America. The first
modern roundabout was constructed in New York
City in 1904. The widespread use of roundabouts
began when British engineers reengineered 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 junctions that have traffic lights.
Roughly the same size as signalized 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.
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.
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In Dublin, 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.
The Kinsale Road Roundabout in Cork 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 kilometer 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.
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 left and other traffic, enabling those
making left 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 on the N2/M50 intersection
in Dublin.
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 circles.
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 signs used to
distinguish mini roundabouts from larger ones.
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A
mini-roundabout, where a painted white
circle is used for the centre. The
arrows show the direction of traffic
flow.
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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.
"Magic" Roundabouts
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 name comes from a similar junction
in Swindon, whose name is derived from the children's
television series The Magic Roundabout.
It was constructed in 1973 to reduce the
congestion at the original standard layout
roundabout where seven roads intersected,
it was one of the first bi-directional
roundabouts to be constructed in Britain.
At the junction of each road with the roundabout,
a mini-roundabout is present and subject
to the normal clockwise direction of travel
for all traffic. Between these mini-roundabouts
however traffic is permitted to travel
clockwise or anti-clockwise around the
larger roundabout, the expectation being
that drivers would choose the shorter route
with less stationary traffic.
When it opened in June 1973 a police officer
had to be stationed at each of the mini
roundabouts to prevent chaos.
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Line
drawing of the roundabout in Hemel
Hempstead, Hertfordshire, England.
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When the new junction was first opened,
a camera was placed overlooking the roundabout on the roof
of the adjacent Kodak HQ building. It was noted many drivers
would get 'lost' and make repeated reversals of direction
between joining the roundabout and eventually leaving it.
The road labelled '2' is the dual-carriageway
St Albans Road and provides the main access to Hemel from
the M1 motorway. Shortly after the opening, the driver
of an articulated lorry failed to understand the new junction
so tried to drive straight across the middle. Given that
there is a river in the middle, which is not visible from
the road, his vehicle got stuck on the middle of an island
in the middle of the river in the middle of the roundabout,
right in the middle of Hemel Hempstead.
The Roundabout Appreciation Society (UKRAS)
is a group of people in the United Kingdom that discuss
various aspects of traffic roundabouts. The main topic
of discussion is the architecture of the roundabouts, including
their general design and any specific safety features.
Other topics have included the various approaches people
take when driving towards and around a roundabout, and
the wildlife present on some of the larger junctions. Their
aim is to promote safe driving and consideration towards
other road users. The society was formed by Kevin Beresford
after the success of a calendar that showed photographs
of 12 roundabouts in Redditch – it sold 100,000 worldwide.
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