DATE OF PROPOSAL
March 31, 1998
SUBMITTING ORGANIZATION
FGDC Ground Transportation Subcommittee
POINT OF CONTACT
Bruce D. Spear, U.S. Department of Transportation, Bureau of Transportation
Statistics (BTS), (202) 366-8870, bruce.spear@bts.gov
OBJECTIVES
To provide a logical data model for identifying unique road segments which are
independent of cartographic or analytic network representation. These road segments will form the basis
for maintenance of NSDI framework road data (through transactions or other means), and for establishing
links among road segments and attribute data.
SCOPE
In accordance with the FGDC Standards Reference Model, the NSDI Framework Transportation
Identification Standard is being proposed under the classification of a data content standard. However, it also
includes mandatory standards for assigning and reporting identification codes as well as voluntary guidelines
for data collection under the classification of a process standard.
This standard will specify a conceptual model for identifying physical road segments that are temporally
stable and independent of any cartographic representation, scale, level of detail or network application, and
a process for combining the road segments to create topologically connected analytical networks. The
model will include a set of locational descriptors for each road segment included in the NSDI framework
road layer, and a format for a unique identification code to be assigned to each identified segment. The
standard will also specify a process for assigning, modifying and recording road segment identification
codes.
Guidelines for selecting and locating the end points of appropriate road segments will be included as an
informative appendix. The user of the standard does not have to follow the guidelines to be in conformance
with the standard.
The basic road data model can be extended to cover other transportation networks including railroads,
commercial waterways, pipelines, and public transit guideways. Other network layers may require different
process standards for assigning and recording identification codes. These additional process standards are
not included as part of this initial standard.
JUSTIFICATION/BENEFITS
There are currently no national standards for identifying, segmenting, or
representing road segments in digital geo-spatial databases. Database developers segment road networks
to satisfy their specific application needs; however, the specific segmentation scheme may not be
appropriate for other applications. Furthermore, there is no standard approach for documenting the
relationship between a digitized road segment and the physical road feature that it represents. Consequently,
the exchange of attribute information between two different road databases representing the same geographic
area is difficult, time consuming and error prone.
A national standard for identifying and documenting road segments will facilitate data exchange among
different users by providing well defined, common reference segments that are tied to the physical road
feature, rather than to any cartographic or network abstraction of that feature. Furthermore, the proposed
standard road data model will allow users to create customized topological networks from the reference
segments without modifying the properties of the reference segments themselves. This will facilitate
transactional updates to framework road databases by allowing new road features to be added without
changing existing road segments.
DEVELOPMENT APPROACH
A Road Data Model Team will be assembled to review the technical
development of the standard and to provide appropriate outreach to the transportation community. (See
POTENTIAL PARTICIPANTS, below.)
An initial draft of the road data model will be prepared under contract, funded by BTS (in progress). The
initial draft will be based, in large part, on the preliminary road data models emerging from the NSDI
Framework Road Data Modeling Workshop, held at Wrightsville Beach, NC, in December 1997. These
preliminary data models are compatible with the generic linear data model developed under the National
Cooperative Highway Research Program (NCHRP) Project 20-27.
The initial draft will be reviewed by the Road Data Model Team and revised based on concerns and
recommendations expressed by team members. Depending on the nature of the review comments, one or
more meetings may be convened to resolve differences among the team. Team members will also be
responsible for informing their constituencies about the road data model standard and for collecting and
summarizing the requirements of their respective stakeholder groups.
The road data model development effort will be closely coordinated with NCHRP Project 20-27 (Phase 3),
which focuses in the development of implementation guidelines for multimodal transportation location
reference systems. It will also provide a focus for possible follow-up workshops to Wrightsville Beach.
Once there is general agreement among the Road Data Model Team that the model meets agreed-upon
requirements, the model will be submitted for formal public review through the FGDC's Standards
Development Process.
DEVELOPMENT AND COMPLETION SCHEDULE:
- Solicitation and selection of Road Data Model Team - May 1998
- Initial draft of road data model by BTS contractor - November 1998
- Review and revisions to road data model - December 1998
- at least one meeting of the full team will take place after the initial road data model has been
delivered and distributed to team members.
- team members will be responsible for informing and soliciting feedback from their
constituencies about the standards development effort through presentations at annual
meetings, articles in newsletters, etc.
- the road data model will be prototyped on one or more road databases to assess
implementation and maintenance issues, requirements for additional tools, etc.
- Revised draft of Transportation Identification Standard prepared by BTS contractor and approved by majority
of road data model team - April 1999
- Transportation Identification Standard submitted for public review through FGDC - January 2000
- Informational presentations on road data model to be made at major transportation and GIS
conferences, including TRB, GIS-T Symposium, etc.
- Final Transportation Identification Standard approved as FGDC standard - June 2000.
RESOURCES REQUIRED
Funding support for contractor to prepare initial road data model and to revise
model in response to review comments will be borne by the Bureau of Transportation Statistics.
Participation on the Road Data Model Team will be on a voluntary basis. Time spent by team members to
familiarize themselves with the NSDI framework and linear data models, review draft documents, participate
in team meetings, and serve as liaison to their respective constituencies will be borne by each team member's
agency or organization. Some additional FGDC funding may be needed to support travel to meetings for
some team members.
POTENTIAL PARTICIPANTS
Team members will include representatives from the FGDC Ground
Transportation Subcommittee, Facilities Working Group, Base Cartographic Subcommittee, Cultural and
Demographic Subcommittee, and Framework Focus Group. Additional representation will be sought from
key transportation and spatial data stakeholders, including the Transportation Research Board (TRB) GIS-T
Task Force, the Intelligent Transportation Systems (ITS) standards working group, the American Association
of State Highway and Transportation Officials (AASHTO), the Open GIS Consortium (OGC) Transportation
Work Group, NSGIC, NaCO, and other interested stakeholders.
RELATED STANDARDS
There are a number of standards for roads and other transportation currently
being promulgated by different stakeholders. In general these standards have been designed to meet the
specific requirements of the stakeholder groups sponsoring their development, and do not generally satisfy
the basic NSDI requirements for database sharing and transactional updating. Nevertheless, these standards
will be investigated as part of this development effort to determine commonalities and opportunities for
integration.
The ITS Standards and Protocol Subcommittee has proposed adoption of the Geographic Data Files (GDF)
as its standard for digital road databases. This standard does not meet all of the requirements of the broader
GIS for transportation (GIS-T) community, particularly with respect to location referencing.
The DIGEST/Vector Product Format standard is an interchange standard for spatial data used by the U.S.
Department of Defense, NATO, and the Transportation Association of Canada. DIGEST/VPF. This
standard, like GDF does not meet all of the requirements of the GIS-T community.
A draft Transportation Network Profile (TNP) was developed for the Spatial Data Transfer Standard (SDTS)
several years ago, but was never submitted for formal adoption due to a number of unresolved issues.
Adoption of a standard road data model may help resolve many of these outstanding issues, and lead to
resumption of the SDTS TNP development.
A Ground Transportation Data Content Standard is being proposed to provide a common set of
entity/attribute/domain definitions for transportation features. These two efforts will be closely
coordinated, and the road data model will provide the foundation on which transportation features in the
content standard will be defined.
ITS is also proposing the establishment of a national linear datum, consisting of well defined and accurately
located control points from which linear measurements can be made along a road segment. The proposed
road data model is compatible with the ITS linear datum. Every effort will be made during the development
of the road data model to maintain this compatibility so that framework road segments can fully utilize the
linear datum, if it is actually implemented.
OTHER TARGETED AUTHORIZATION BODIES
None at this time. However, depending on the
acceptance of the proposed road data model by the transportation community, it may be appropriate to
submit it to ANSI and ISO at a later date.
