Highway exchanger

Definition

One calls exchanging highway the systems of road “straps” allowing to engage on a Fast track, or a Autoroute or to leave them to take another highway or a road of the ordinary Highway network. The exchangers are thus with the intersections between highways, or a highway and another type highway. They make it possible to avoid any crossing on level to limit the deceleration the ways concerned.

A highway exchanger at least counts a bridge making it possible a highway to span the other. In the most complex cases, the roadways can be staged on four different levels (exchanger known as " Furnace-stack").

An exchanger can be complete (bidirectional) or partial (giving access to only one direction of the highway).

Environmental impacts

Compared to the Roundabout, the exchangers strongly increase the influence on the ground and the consumption of space (cultivable, inhabited or supports of natural habitats). In addition, the exchangers encourage and facilitate the speed and thus the fuel consumption and the emissions of Gaz to greenhouse effect. They finally contribute, generally, to create phenomena of ecological Insularisation, of Roadkill, to increase the ecological Fragmentation. Concerning the night Environment, being often very enlightened, they can contribute to the phenomenon known as of “ luminous Pollution ”. For residents when there is, they pose problems of noise pollutions difficult to regulate because of variations of levels which returns the anti-noise walls less effective (when there is, which is very seldom the case for the exchangers), all impacts which the impact studies should take into account and translate into term of Conservative measures (écoduc S possibly) or Compensatory measures, which are obligatory - at least for the great projects - in a growing number of country since the years 1970. On the ways very circulating, the fuel profit permitted by the least need to slow down and start again (compared to the roundabout or more still with the signal-controlled junction), to some extent is lost by the additional length of the straps, deceleration in the curves and strong acceleration often necessary for the insersion in the circuation of the main roads.

The nature and the extent of the environmental impacts depend on the natural and human context, but also on the type of highway exchangers, whose the principal variable ones are presented below:

Types of exchangers

Clover exchanger

It is one of the very first types of exchangers, appeared in the Thirties with the the United States. It is very much used also in Germany. It is a massive exchanger, requiring a very great influence, and which is generally justified by an important traffic. Model Ci above also includes/understands the collecting side ones, intended to avoid the crossings of flow of circulation. The cloverleafs are rather not very current in France. One finds some however for example with the crossing A30 - A31 in the north of Metz, or with the crossing A86 - N7 with Rungis

Exchanger 4-stack

The 4-stack is the most massive type of exchangers existing. Conceived so that no traffic crosses, it is built on four levels: certain exchangers with the the United States thus reach the 25 meters height! There remains intended for a very important traffic, and is rather rare in Europe: one finds of them some with the the United Kingdom, and one or two in Spain, Italy and with the Netherlands. There does not exist any 4-stack complete in France. Only envisaged was located at Palaiseau, with the current crossing of the highways A10 and A126. There remains always unfinished since the abandonment of the prolongation of A10 until the Ring road of Paris, in 1977. It is however envisaged or to supplement it in the medium term, or to remelt the exchanger completely.

See too

Road
Highway
Congestion
Road HQE
Studies of environment of a road project

External bonds

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