14.5 Signals that apply to multiple roads

ASAM OpenDRIVE offers the possibility for one signal to apply to multiple roads. This is achieved by defining the signal in one road using a <signal> element, and referencing it from one or more other roads using <signalReference> elements. This is especially useful in junctions where many roads are close together and, for example, speed limit signs may need to apply to more than one of those close-together roads.

The <signalReference> element shall include the longitudinal, @s attribute, and lateral, @t attribute, position on the road where the referenced signal should take effect. The <signalReference> element shall also include an @orientation attribute to specify whether the referenced signal applies to traffic flowing in the positive, negative, or both s-directions. Similarly to <signal> elements themselves, <signalReference> elements may be supplemented with an <validity> element for lane validity. This makes it possible to include or exclude certain lanes from the signal’s validity range.

Elements in UML model

<signalReference> element

In ASAM OpenDRIVE, a referenced signal is represented by the <signalReference> element within the <signals> element.

UML class: t_road_signals_signalReference
XML tag:   <signalReference> (Multiplicity: 0..*)

Refers to the same, that is, identical signal from multiple roads. The referenced signals require a unique ID. The <signalReference> element consists of a main element and an optional lane validity element.

Table 124. Attributes of the <signalReference> element
Name Type Use Unit Description

id

string

required

Unique ID of the referenced signal within the database

orientation

e_orientation

required

"+" = valid in positive s-direction
"-" = valid in negative s-direction
"none" = valid in both directions

s

t_grEqZero

required

m

s-coordinate

t

double

required

m

t-coordinate
img
Figure 130. UML model of the t_road_signals_signalReference element in the Signals class

Figure 130 shows the UML model of the t_road_signals_signalReference element in the ASAM OpenDRIVE Signals class.

<validity> element

In ASAM OpenDRIVE, lane validity is represented by the <validity> element within the <signal> or <signalReference> element.

UML class: t_road_objects_object_laneValidity
XML tag:   <validity> (Multiplicity: 0..*)

Lane validities restrict signals and objects to specific lanes.

Table 125. Attributes of the <validity> element
Name Type Use Description

fromLane

integer

required

Minimum ID of the lanes for which the object is valid

toLane

integer

required

Maximum ID of the lanes for which the object is valid

XML example

Rules

The following rules apply to referencing signals from multiple roads using the <signalReference> element:

  • A lane <validity> element may be added for every <signalReference> element.

  • Signal reference shall be used for signals only.

  • The direction on the road for which the referenced signal is valid shall be specified for every <signalReference> element using the @orientation attribute.

  • The range given by all <validity> elements shall be a subset of the parent’s @orientation attribute:

    • For right-hand traffic, @orientation="+" implies that the <validity> element shall only span negative lane ids, while @orientation="-" implies that the <validity> element shall only span positive lane ids. If the given <validity> elements span both, positive and negative lane ids, @orientation="none" shall be used.

    • For left-hand-traffic, @orientation="-" implies that the <validity> element shall only span negative lane ids, while @orientation="+" implies that the <validity> element shall only span positive lane ids. If the given <validity> elements span both, positive and negative lane ids, @orientation="none" shall be used.

  • The value of the @fromLane attribute shall be lower than or equal to the value of the @toLane attribute.

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