Article citation information:
Macioszek, E. Roundabouts
as aesthetic road solutions for organizing landscapes. Scientific Journal of Silesian University of Technology. Series
Transport. 2022, 115, 53-62.
ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2022.115.4.
Elżbieta MACIOSZEK[1]
ROUNDABOUTS AS AESTHETIC ROAD SOLUTIONS FOR ORGANIZING LANDSCAPES
Summary. In the
transportation systems are different types of intersections. Among them,
roundabouts are considered the safest solution. The application of roundabouts
is conditioned by many factors. One of them borders on area development.
Roundabouts, among others, are localized in important city places, thus serve
as a landmark in the city or are localized on the boundaries of areas with
different communication functions, thus constituting an organizational
landscape feature. Sometimes, they diversify the space of a street or close the
perspective of a monotonous street. Hence, beyond the basic functions,
roundabouts with the appropriate central island arrangements can also play the
function of organizing the architecture of the local area. The ways and
possibilities of roundabout central island arrangements are presented in this
article. An interesting central island arrangement shows that roundabouts play
an esthetic and organizing landscaping role.
Keywords: roundabouts,
central island, esthetic, road solutions, civil engineering, transportation
1. INTRODUCTION
Cities and
urban agglomerations development contribute to transport networks thickening,
which is necessary to obtain efficient connections between different points in
a transport network [11]. These networks consist of linear elements - roads, as
well as point elements - crossroads. Over the last nearly thirty years,
intersections like roundabouts are a keen and often designed transport systems
elements. Roundabouts are also the subject of multifaceted scientific research
relating to their functioning, efficiency, capacity, and many other issues [1, 4,
8, 10], as well as relating to their functioning as the transport network
elements or transport systems elements. Roundabouts have gained wide popularity
and favor from the designers because of their high level of road traffic
safety.
The most basic form of a roundabout intersection is the single-lane
roundabout. Single-lane roundabouts provide a higher level of road traffic
safety than other types of intersections [6]. It is mainly caused by such
roundabout features as a reduced number of collision points, low crossing
speeds (from the scope of 15-
The characteristic features of a turbo roundabout include [7]:
- no more than two lanes in the roundabout
circulatory roadway in the area of the inlets,
- without ring widening, it is
impossible to turn in one of the traffic directions,
- no possibility of maneuvering
the intersection streams of vehicle in the area of the roundabout circulatory
roadway, due to the use of a horizontal marking together with the spiral shape
of the roundabout circulatory roadway (it leads to a reduction of the number of
collision points),
- the presence of more than one
traffic lane on the roundabout circulatory roadway,
- relatively low speed through
the roundabout, resulting from traffic separators and specific roundabout
geometry,
- the possibility of achieving a
higher value of capacity compared to a two-lane roundabout,
- the possibility of selecting a
driving direction only at the entrance to the roundabout.
However, it should be noted that for technical reasons including problems
of snow removal, rainwater drainage, traffic share of heavy vehicles and social
problems, for example, the problem of non-acceptance of new road solutions by
the public on some turbo roundabouts in Poland, no permanent traffic separators
were installed raised above the road surface.
The basic geometric elements of a roundabout include the central island of
the roundabout, the splitter islands at the inlets, the circulatory roadway of
the roundabout, inlets and outlets.
Subsequently,
there are three types of islands designed at roundabouts. There are central
island, islands dividing traffic flows at the entries (splitter islands), and -
if necessary, given a traffic lane conducting traffic flow outside the
roundabout in a right turn relation – lateral islands. According to
Polish Guidelines [3], a roundabout central island should be located in the
middle of an intersection and be circular in shape (in exceptional cases, a
shape that is close to a circle). Small, medium and large roundabout’s
central island may be impassable because the central island arrangement and
border curb around the island prevents vehicle entry. In the case of mini-roundabouts,
the central island is designed to allow passing long vehicles across the island
by the design and pavement surface. In turn, according to the same Polish
Guidelines, islands dividing traffic flows at entries are defined as islands,
which separate the entry from the exit and traffic flow entering into the
roundabout main roadway from traffic flow exiting from the roundabout main
roadway. In roundabouts, the lateral island may also be designed. This type of
island has separate traffic lanes dedicated to turning right vehicle drivers
from the roundabout main roadway. Among these three types of islands, the
central island is the most important functional element of the roundabout. The
central island determines the size of the occupied area by the roundabout,
dictates the road traffic safety in the area of the roundabout, as well as the
aesthetics of the whole intersection. Both central island dimensions and height
have significant effects on a roundabout’s recognizability and
legibility. Apart from the central island operational functions and functions
resulting from the roundabout geometry, it also allows for an interesting
arrangement.
The
central island arrangement of roundabouts localized in urban areas may be
interesting and refer to the surrounding and other elements of city zoning.
Whereas central island arrangement of roundabouts localized outside urban areas
may refer to the specifics of the surrounding landscape. The ways and
possibilities of central island arrangements of roundabouts localized in Poland
and other countries in the world are presented in this article.
2.
WAYS OF DEVELOPING CENTRAL ISLANDS IN ROUNDABOUTS
Nowadays, the main
purpose of roundabouts design and construction is primarily to ensure a high
level of road traffic safety and meet the desired capacity in transport system
networks. Roundabouts are attractive alternatives for canalized intersections
and intersections with traffic lights. The advantages of roundabouts predispose
them to their use, both in urban and outside urban areas. Today's
roundabouts are characterized by a very diverse form of functional and
organizational solutions, location in the urban space and elements of the
arrangement of the central island. Roundabouts are important elements of the
urban landscape. From the perspective of spatial composition, they are the
elements that crystallize the city plan, the dominants of the spatial
arrangement, outstanding elements of the landscape, as well as nodal points and
special elements in the transport networks. In large cities, roundabouts are
built at the junction of major roads: roadways and tram tracks. They are an
important element of the communication network and, as such, must provide
drivers with the possibility of efficient and safe travel. However, the large
area normally occupied by a roundabout can be used in other ways. Planted with
plants and well lit, and therefore visible at dusk and night, it will become a
decorative element in the urban space, breaking the ugliness of big streets
full of noise and exhaust fumes. The attractiveness of roundabouts is evidenced
not only by the area or location but also by the development idea.
The central island,
the external diameter of the central island, height formation and arrangement
are some of the basic geometrical elements of small, medium and large
roundabouts. From the viewpoint of road traffic safety, it should be borne in
mind that the larger the size of the central island, the greater will be the
vehicles’ speed on the roundabout. The guidelines [3] recommend that
the central island be circular circularly shaped, ensuring constant curvature
for internal arcing of the main roadway of the roundabout. The oval central
island shape in the same guidelines is not recommended for designing.
The center
part of the central island should be clearly visible from all the roundabout
entries and create an optical obstacle for vehicle drivers approaching the
roundabout. Designing a high central island creates an optical obstacle for
vehicle drivers approaching the roundabout so that vehicle drivers can focus
their attention on vehicles approaching from the left side without any
unnecessary deconcentration by the observation of traffic flow on the opposite
side of the roundabout.
The most
common solution is the central island arrangement with greenery (low, medium,
high, very high or a mix of them - Figure 1).
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b). |
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c). |
d). |
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Fig. 1. Central island arrangement with the use of
a) low greenery in the roundabout localized in Radzionków, b) high
greenery in the Wileńskie Roundabout localized in Rybnik,
c) very high greenery in the large four-lane roundabout localized in China,
d) very high greenery in the large two-lane roundabout in Budapest
Source: authors’
documentation
The choice of species
of trees and shrubs for planting depends on climatic conditions, particularly
the temperature in winter. In addition, applied trees and shrubs should be
resistant to air pollution and soil (mainly salinity), which in urban conditions
and along roads with heavy traffic is very important. The shrubs (for example,
meadowsweets, cotoneasters, berberis, cinquefoils), coniferous plants (for
example, arborvitaes, junipers), ground cover plants which do not require
frequent treatments (for example, roses), annual plants selected based on the
time of year (for example, pansies, bechases, marigolds, geraniums, ageratums,
salvias), grasses and perennials (for example, berges, crinoids), are readily
planted on the central island. Most of these plants are resistant to drought
and do not require frequent watering.
Besides
the greenery, on the roundabout central islands, small architectural objects
are used. These are small building structures constructed within the framework
of land use. In the case of the central island of roundabouts, such elements as
sculptures, figures, statues, fountains, small rock gardens, shrines or
elements referring to the surroundings are used (Figure 2a). Sometimes,
lighting is placed on a roundabout’s central island. Lighting provides a
good roundabout roadway visibility at dusk and night, even from a distance.
According to [9], during
the central island arrangements designing process, the following should be
considered:
- ensure the visibility of the intersection area for drivers
both approaching the roundabout as well as driving on the main road of the
roundabout,
- the fact that the design on a central island should be
solid objects and not sliding obstacles such as trees, walls, columns,
sculptures, or large boulders that may pose threats to both drivers and
passengers after falling out of the roadway (Figure 2b),
- the fact that the central island can serve as a
gateway between city areas with various communication functions. Thus, drivers
will be in a different communication zone after crossing the roundabout,
- the need to plan the maintenance schedule and care of
the central island during the roundabout operation,
- the additional costs associated with the project,
arrangement and maintenance of the central island.
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b). |
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Fig. 2. Central island
arrangement in roundabouts localized in Rybnik
a) by elements appeal to surroundings in Boguszowickie Roundabout,
b) by concrete elements localized circumferentially in Mikołowskie
Roundabout
Source:
authors’ documentation
3.
CENTRAL ISLAND ARRANGEMENTS AT ROUNDABOUTS IN POLAND
In
Poland, roundabouts are a popular intersection solution. The first modern
roundabouts in Poland were built in the early nineties of the twentieth
century. Presently, there are nearly 1500 different types of roundabouts. There
are small, medium, large, one-lane, two-lane, semi-two-lane, spiral- and
turbo-roundabouts. The most popular roundabouts in Poland (above 40) is in
Rybnik city (in 2016, the population was 139 540 people [2]). Figure 3 presents the
various possibilities of central island arrangements at roundabouts in Rybnik.
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b). |
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Fig. 3. Central island
arrangements in roundabouts localized in Rybnik
a) by components touches on the nature of the surrounding,
b) by components of small architecture
Source:
authors’ documentation
Whereas
the biggest roundabout in Poland, at the same time one of the largest in
Europe, is the roundabout named “Constitution 3rd of
May” in the center of Głogów city. Its central island has an
area of approximately
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b). |
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Fig. 4. Central island with
special traffic lanes for oversize vehicles
Source:
authors’ documentation
At
roundabouts, sight distance decides the size and type of materials to be used
for its central island arrangements. Another important element of the design of
the central island arrangement (type, selecting plant materials, and other
landscape features) is the speed of the roadway, because, at low speeds at
roundabout entries, the potential risk of traffic incidents is small, while at
higher speeds, the potential risk of traffic incidents increases. Furthermore,
the type of central island arrangements should discourage pedestrians from
going through the central island. During the design of roundabouts central
island, elements that attract pedestrians, for example, benches, stairs, and
pavement tiles, should be avoided.
4. CENTRAL ISLAND ARRANGEMENTS AT
ROUNDABOUTS AROUND THE WORLD
Despite existing
restrictions on the development of central islands, diverse and often
interesting examples of central island arrangements can be found in different
countries around the world. An example is Parisian roundabouts with their
unique representational architecture. One of them is “La
Place de l’Etolie”. There is the first roundabout built in Europe.
On the central island is localized the Arc de Triomphe (Figure 5). Another
example of an interesting arrangement of a central island in Paris is the
central island roundabout localized near the
Louvre Museum, which is an important element of the city's image (Figure
6).
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b). |
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Fig. 5. La Place de l'etoile in
Paris (France) with Arc de Triomphe localized on
the central island
Source: authors’
documentation
Roundabouts are often
localized near shopping centers to ensure safe access to and from the shopping
centers. On a central island, a variety of plants and compositions consisting
of rock formations or colored
stones can be used (Figures 7 and 8).
Some central islands have not only aesthetic but also bear hidden
ideological messages. Further, in the arrangement of central islands, fountains should
only be used in areas without strong winds. Otherwise, the water spray they
generate may adversely affect drivers’ visibility in the area of the
roundabout (Figure 9).
Fig. 6. An interesting
arrangement of a central island with the use of low greenery
in the roundabout localized near the Louvre Museum in Paris (France)
Source:
authors’ documentation
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b). |
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Fig. 7. The arrangement of
central islands with the use of
a) sculpture and high greenery in the roundabout localized in Athens (Greece),
b) low greenery in the turbo roundabout localized in Szeged (Hungary)
Source:
authors’ documentation
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a). |
b). |
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Fig. 8. The arrangement of
mounted central islands with the use of colored stones
in roundabouts a). localized in Krk island (Croatia), b). localized in Varna
(Bulgaria) Source: authors’ documentation
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b). |
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Fig. 9. The arrangement of
central islands in roundabouts localized in Agadir (Morocco) with the use of
a). fountain, b). average greenery
Source:
authors’ documentation
5. CONCLUSIONS
The traditional
roundabout is a crossroad without traffic lights, where traffic moves around
the central island. In comparison to other intersection solutions, the
roundabout is more efficient, performing many functions simultaneously, for
example, regulation and traffic calming. Single-lane roundabouts are
particularly popular due to their ability to increase traffic flow and
improvement of safety. However, errors in decision-making and misunderstanding
of road traffic rules by drivers lead to collisions in traffic directions on
circular lanes of multi-lane roundabouts. Although these incidents are not
serious, they are nonetheless common and impede traffic flow.
Roundabout central
island arrangements are recommended due to their roundabouts functions and
positive role in noise suppressing and exhaust emissions reduction. The most
common solution in the arrangement of roundabout central islands is the use of
low, medium and high greenery. The potential barrier in the central island
design is the non-obscuring visibility condition. Besides greenery, diverse
interesting ways of designing central islands are developing in Poland and
other countries of the world. The benefit of an interesting arrangement of the
central island is one of the distinguishing features that give such
intersections like roundabouts an aesthetic advantage over the traditional
ones. Proper arrangement of the central island enhances the community and
improves public safety. Sometimes, roundabout central islands are used for
displaying local arts or as gateway features. On some roundabouts, the central
island is illuminated at night. Various things can be found on central islands,
for example, plant and plant-rock compositions, which undoubtedly, augment the
aesthetic value of roundabouts. Some of these aesthetics have hidden
ideological undertones.
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Received 19.01.2022; accepted in
revised form 17.03.2022
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