1.5. Hierarchisation ofroadways in urban environment
The conclusion at which we arrives according to a study of
STRANSKY (1995), is that the behavior of a motorist, which can result in speed
that it practices on an axis given, is influenced by the elements of the
surrounding visual scene and thus can force it to adopt changes. From this
assertion, it results from it that speed practiced on a way is function of the
installation of this way. Thus, it appears for reasons of functionalities,
safety and economy, useful to adapt each section of roads during its
construction or of its requalification to the function awaited from this one
(influence of the function on the form): from where concept of hierarchisation
of the ways in urban environment.
Indeed, it is at the time of Chatre of Athens in
1933(CORBUSIER, 1957)which one really starts to grant an importance to the
adaptation of the road to the car. And due, this one did not correspond any
more to the old characteristics of the street as well by its new geometrical
characteristics, mechanics as by its speed.
The «rule of the 7V» is one of the
first rules of hierarchisation which was formalized by UNESCO in 1948(d'ARCIER,
1992, p. 27). It consists of:
V.1: national road or of province crossing the country
or the continents
V.2: municipal, standard creation of arteries
essential for an agglomeration
V.3: held primarily for mechanical circulations, they
do not have a pavement; no door of houses or buildings opens on them.
Regulating fires of colors are laid out the every four hundred meters, thus
allowing the vehicles a considerable speed. V.3 has as a consequence, a modern
creation of town planning: the sector.
V.4: the commercial street of sector
V.5: penetrating in the sector, it drives the vehicles
and the pedestrians to the doors of the houses, with the assistance of
V.6
V.7: feeding all with length the green zone sees where
are the schools and the sports.
V.8 came since, channeling the
bicycles.
By what precedes, it appears that the hierarchisation of the
roadway system in urban environment does not date nowadays and wants to be to
be a means of representing a network of ways starting from several beforehand
definite criteria. It is a tool for analysis, meeting a need for classification
and organization of the network of circulation. It can also be useful during
the programming of installations, to which it is used as reference(CERTU,
2008). It thus makes it possible to obtain profits in terms of safety, in
particular by a greater coherence between classes of ways and thus by a better
legibility of the network for the users. Nowadays, the possible forms of
hierarchisation many according to whether one is in urban environment or are
perished urban.
For the ways in urban environment, the forms of
hierarchisation are more complex. Thuswe have a hierarchisationwhichcanbe:
· Functional according to the type of connection, for
example: primary ways (structuring), secondary (distribution), tertiary sector
(service road);
· By typology according to the influence of the way in a
logic of urban development (urban fast tracks, boulevards, avenues, streets...)
;
· By typology of way according to the nature of the
bordering frame (in withdrawal, alignment, height...);
· By typology according to the social practices (local
life, places emblematic...) ;
· By an analysis multicriterion integrating the multiple
uses and needs for public space.
Hierarchisation rests more and more on the taking into account
of two principal functions: the function
«circulation» which milked with the flow that can
run out the way, and the function «local life» which
is concerned with impacts that the road has on the traversed environment. It is
thus question here of safety of the residents.
One defines the class of way according to the preponderance
granted to such or such function. The characteristics desired for these classes
must correspond to the objectives initially envisaged in the documents of city
planning namely: share roadway system, development of the alternative means of
transport, safety of the users.
Today with the example of the European countries, Germany in
particular, a hierarchy resting on two great levels is usually advised with:
· main roads where the circulatory function is dominating
on the function local life. The organization of space on these ways is
structured in theory (crossroads, crossed pedestrians...);
· zones with alleviated circulation, generalized on most
of the urban territory, but also of the zones of meeting and surfaces
pedestrians, to privilege the local life and to ensure the safety of the
various uses of the network, by moderating speeds and by eliminating the
parasitic traffics in these zones.
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