Image (road signs)

In road signs, the perception which the user has of a pole (agglomeration, city, service, etc) is called image of this pole. It depends on the one hand on the importance of the pole, on the other hand of the distance of the user compared to this one.

Definition

If a Usager is located in a point O distant from E_OA of a pole has, the pole has appears all the more important to him as its approximate level N_A is higher and that E_OA is weaker.

The studies of accessibility resulted in representing this phenomenon by the concept of image of the pole saw O whose expression is:

I_OA = N_A - E_OA

Domination

Are two poles has and B one says that has dominates B, so for any item 0 such as B is between 0 and has, one a: I_OA > I_OB

The concept of domination of B by has thus means that, although more distant from 0, the pole has is gravitational than the pole B.

This concept is independent of the point of observation and can result in the condition: N_A - N_B > E_AB

Conventions of application

the phenomenon of domination is taken into account only between poles of different classes (and not of different levels).
In order to limit the range of the domination, one is appropriate of the following rule. That is to say a pole has approximate level N_A likely to dominate a pole B of approximate level N_B; if (N_A - N_B) > 1, one imposes for the study of the domination: N_A = N_B + 1

This convention means that one limits the domination to a maximum distance of fifteen minutes.

When a pole B is dominated by a pole dominated itself by a pole Z such as has is between B and Z, the domination of Z on has can be taken into account only starting from B.

Domination of the starting pole on the pole of arrival

When the pole of arrival of a connection is dominated by the starting pole of this connection it does not ensure, in general, a relay sufficient for the user located inside the pole thus dominating since the center of a city, a commune of suburbs does not constitute a relay sufficient for I' user wishing to go beyond the agglomeration.

It is considered whereas the dominated pole does not make any more screen. This makes it possible to restore one Connection with a pole not dominated located beyond.

Thus any pole dominated B is " transparency with respect to a pole C not dominated of the same class under the following constraints:

that I' route AB is I' route " naturel" (with the glance it traffic) to go from has to C
and that the rule of maximum distance between has and C is respected.

Domination of the pole of arrival by a pole located beyond

When a pole is dominated it is, generally, gravitational for I 'user than the pole located beyond and which dominates it; thus a commune of suburbs is, in general, gravitational, for I 'user coming by far, that the city centers agglomeration.

It is considered whereas the dominated pole does not make any more screen; this makes it possible to restore a connection with the pole dominating located beyond. In this case, the connection finishing with the dominated pole is taken into account only as from the moment when I' attractivity of this dominated pole is sufficient.

Thus any pole dominated B is " transparent" with respect to a pole has which dominates it provided CB is the route “naturel" (within the meaning of the traffic) to go from C to A.

Item 0 ' is given according to the cases below concerning b:

green Mention dominated in open country: item 0 ' is the first important crossroads such as E_{O' B} < N_B
white Mention dominated in open country: item 0 ' is the first crossroads such as E_{O' B} < unspecified N_B/2
Mention dominated in urban environment: the O' point is the first crossroads such as E_{O' B} < N_B/2

Sources

interdepartmental Instruction of March 22nd, 1982 relating to the indication of direction.

See too

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