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ITN Road Routing Information (RRI) theme
Go to: Theme definition | Simplification and priority of routing information | Explicit and implicit drive restrictions | Representation of captured information
In OS MasterMap® Integrated Transport Network™ Layer (ITN), the Road Routing Information theme provides information that may affect a driver’s choice of route. That information could be either restriction information, such as a prohibited turn, or advisory information, such as the presence of a ford.
Within ITN, routing information is maintained as separate features from the network. These RRI features reference the underlying road network features, RoadLink or RoadNode features, to provide their location. The relationship between the RRI features and the physical features they provide information about is described in the Road and RRI relational model.
Theme definition
Description: Information, referencing features in the Roads Network theme, that may influence a driver’s choice of route.
Theme rule: theme = ‘Road Routing Information’
Features:
- RoadNodeInformation
- RoadLinkInformation
- RoadRouteInformation
- RoadPartialLinkInformation
- RoadPartialRouteInformation
Simplification and priority of routing information features
RoadRoutingInformation features attempt to model the effect and nature of real-world restrictions or environmental factors. However, this is not always possible as restrictions, in particular, may manifest themselves in many different ways yet have the same effect.
For example, a single restriction may consist of a one-way street that has a no entry sign, no right or left turn signs and possibly mandatory turn signs on the approach roads. The simplest way to represent this would be as a one-way street. To ensure a level of consistency, a hierarchy is used when more than one restriction with the same effect occurs at a given location. Only the restriction with the highest priority is captured.
Priority Restriction type
6 One way
7 No entry/access prohibited to/access limited to
8 Mandatory turns
9 No turn
RRI features primarily model the effect of any restriction in the simplest possible way; secondary to this is recording the real-world manifestation.
Explicit and implicit drive restrictions
Explicit drive restrictions are those normally displayed on road signs or painted on the roadway. Examples include ‘turn right’, ‘ahead only’, ‘no left turn’ and so on.
Implicit drive restrictions are turns or changes of direction that are possible, but undesirable or dangerous, because of the position of traffic islands, road markings or lane indicators. Both types of restriction are captured.
Representation of captured information
RRI features are divided into the following five categories.
Information coincident with RoadNode features
RRI features that are coincident with intersections of the base network are captured as RoadNodeInformation features. Typical examples would be mini roundabouts or bridges with a height restriction where one road crosses another.
Information about a RoadLink where direction of travel is unimportant
RRI features that apply regardless of direction of travel to an entire RoadLink, or at a point along a road link, are captured as RoadLinkInformation features. Typical examples of a RRI feature applying to an entire link could be access restrictions such as ‘no access for unauthorised vehicles’, ‘residents only’ or the presence of traffic-calming measures.
Examples of a RRI feature at a specific location on a RoadLink, regardless of direction of travel, are level crossings, gates, fords and height restrictions not associated with a road bridge (that is, not coincident with a RoadNode feature).
Where location along a RoadLink is relevant and available, this information is supplied as both National Grid coordinates and the distance along the link from its start point.
Information about a RoadLink or number of road links specific to a given direction of travel
Route information features that apply in a specific direction of travel to single or multiple RoadLink features are captured as RoadRouteInformation features.
Examples would be turn restrictions (applying to multiple links such as no U-turn), one-way streets (affecting a single link in a specified direction) and access restrictions that apply in one direction only. Where location along a RoadLink is relevant and available, this information is supplied as both National Grid coordinates and the distance along the RoadLink feature from its start point.
Information about part of a RoadLink where direction of travel is unimportant
RRI features that apply regardless of direction of travel to a portion of a single RoadLink are captured as RoadPartialLinkInformation features.
An example would be an access restriction, such as a pedestrianised area, that may be used by vehicles at specific times and only applies to a section of a RoadLink feature.
The start and finish points along the RoadLink feature are supplied as both National Grid coordinates and the distance along the RoadLink feature from its start point.
Information about part of a RoadLink specific to a given direction of travel
RRI features that apply to a portion of a single RoadLink with a specific direction of travel are captured as RoadPartialRouteInformation features.
An example would be an access restriction in one direction only, such as a bus lane, or a one-way restriction that applies to a section of a RoadLink feature.
The start and finish points along the RoadLink feature are supplied as both National Grid coordinates and the distance along the RoadLink feature from its start point.
Further examples of RRI features are shown in ITN GML examples.
In this section:
ITN Technical specification – home
ITN Road Routing Information (RRI) theme
ITN Path Routing Information (PRI) theme
Feature types and attribution in the Road Network theme
Feature types and attribution in the Road Routing Information theme
Feature types and attribution in the Urban Paths Network theme
Feature types and attribution in the Path Routing Information theme
Descriptions of ITN Layer attributes
Attribution checklists for the Road Network and Urban Paths Network themes
ITN attribute definitions and values
This web page is part of the technical specification for OS MasterMap® Integrated Transport Network™ Layer. For the terms that apply to use of this specification, refer to Purpose of this specification.