The location reference schemas are a set of related Express schemes to describe a road network on three interrelated levels : the lane network, the crriageway network and the motorway network. All three network descriptions are based an abstract directed non-planar graph definition.
The following location reference schemas are defined :
See below for additional information and links.
The Road Network Geometry schema provides an abstract specification of a road network as an non-planar, directed graph. The graph is non-planar to support crossing at different levels by means of bridges, tunnels etc. The graph is directed because almost all traffic properties are direction related. The Road Network Geometry schema provides also the definition of some related abstract entities like a route through the graph. A segment defined as a route where you always go straight ahead and never turns right or left. Upstream routes are defined as a set of routes all ending in the intermediate nodes.
The abstract Road Network Geometry schema is the basis for three or more network schemas: the lane network to provide for a description on lane level, the carriageway network for a description on carriageway level and motorway network to provide for a even more aggregated view in which complex intersections may be modelled as single nodes.
The motorway network schema models an aggregation of the carriage way network. Most notably, it may be used to map complex intersection consisting of many carriageway elements into one motorway node.
Its purpose is to provide the facilities for producing overviews of a road network. Eventually one might create more then one motorway network description based on the same carriageway network.
Nevertheless, it is still unclear which meaningful attributes such a moterway network may have.
The carriageway network schema models a road network as a directed non planar graph of carriageway elements and junctions. A carriageway element may be bounded in longitudinal direction by means of a shoulder, a barrier or a ‘blocked’ line.
The basic idea is that if any two vehicles drove over the same a carriageway elements in the same order the necessarily drove the route.
A carriageway network description can be constructed on the basis of a GDF input file.
The lane network schema models a road network as a directed non planar graph of lane elements and junctions. A lane element may be bounded in longitudinal direction by means of a shoulder, a barrier, a ‘blocked’ line or a ‘dashed’ line.
A carriageway network description can be constructed on the basis of a GDF input file (see the section GDF) which also contains the number of lanes of the GDF road elements or GDF road element segments.
The BPS schema models the location references as used by Dutch roadmen and other officers along the national raods.
Note the Express-X mappings between the network schemas on one hand and BPS location references on the other hand and visa versa are still to be defined.
The RDS/TMC schema support the use of Alert-C location references and provides for a mapping of the pre-defined RDS/TMC references to the appropriate road network, which is in most cases the carriageway network.
The applicability of the network location schemas as introduced above can be demonstrated with a few examples.
The basic idea behind this examples is that the phenomena (features) to be describes should not necessarily have fit with the granularity of the network description. Traffic signs and other equipment my be placed or removed anywhere along a carriageway or lane without impact on the description of the network on which they are used.
The basic modelling capabilities of the network location schemas are demonstrated in the following examples.
Application schemas:
Note that in all these examples only some typical location references are modelled and no other attributes.
Porous asphaltSo the use of porous asphalt in a road network can be modelled a set of carriageway
segments with a porous asphalt surface.
Max 100 km/hour roads
Carriageway with a 100 km/hour speed limit may be modelled in the same way as the use of
porous asphalt, i.e. as a set of carriageway segments with a 100 km/hour speed limit.
A little more complicated entity is an incidents. Restricting our view to the location, it happens at some location, it may cause upstream queues form both its own location and (secondary queues) on the carriageway in the other direction because of curious slowing-down traffic
This can be modelled by means of:
- the point on a carriageway at which the incident occurred,
- a set of upstream queues (carriageway routes) ending at this point
- an optional secondary point at the carriageway in the other direction
- a set of upstream queues (carriageway routes) ending at this secondary point
A most interesting application is signalling. As signalling used lane related traffic signs and also the notion of previous sign is very important, signalling is modelled as directed non-planar graph which is mapped on the lane network.
The location of the gantry carrying the sign display units is described by an intermediate node on a carriageway element.
The Road Network Geometry schema is based on the spatioal G0 schema defined in the final draft of the CEN prestandard prENV12160, Novmeber 1996. A partitial schema defintion of Spatial G0 is is included.