Webinar 48
National Road Network

May 24, 2022

Summary of the Federal Highway Administration’s Quarterly Webinar


The Federal Highway Administration (FHWA) promotes geographic information systems (GIS) as a means to more effectively manage and improve transportation systems. One of the ways that FHWA does this is through its GIS in Transportation program1, which identifies timely and critical GIS issues and topics in transportation and connects transportation agencies with available resources and best practices. The webinar summarized here is part of a quarterly series organized through the GIS in Transportation program.

Justin Clarke, Transportation Specialist, and Thomas Roff, Transportation Specialist, of FHWA, presented on FHWA efforts to develop a National Road Network Project (NRNP). As defined by Congress, NRNP incorporates requirements and a process framework to improve the quality of the Highway Performance Monitoring System (HPMS) road network in three areas:

  • Connectivity of networks at intra- and interstate borders,
  • Spatial representation of multi-carriageway roadways, and
  • Spatial accuracy of networks.

The project also identified tools for improved network edge matching and standardized reporting of data that are attached to State linear road networks. The NRNP webinar hosted on May 24, 2022, was attended by 195 participants.

FHWA maintains the HPMS to collect state-level roadway information. Following updates during the last decade, the HPMS now includes state-level spatial road networks for all public roads. HPMS spatial networks (referred to as ARNOLD) are now a critical source for several national applications. ARNOLD is updated annually, directly sourced from State DOTs and includes all public roads.

Although the networks created from HPMS provide extensive, state-to-state connectivity, complete intersection models, and consistent roadway representation between States would increase their application. Recent attempts to use ARNOLD for natural disaster impact assessment have highlighted the need for these enhancements. With dedicated funding from Congress, the FHWA embarked on a project to enhance ARNOLD—the National Road Network Pilot or NRNP—with the goal to produce a national route file with improved spatial network connectivity across jurisdiction lines, refined data to network relationships, and improved spatial accuracy. These enhancements are expected to lead to improved usability of ARNOLD for applications including travel monitoring, safety analysis, freight modeling, and emergency response.

National Network Schematic Chart

ARNOLD generates national network connectivity, which is the key access point to illustrate Agencies’ convergent needs and goals. Consistent research, input from previous data submittals, clear base guidelines, and communication and coordination skills with other States and U.S. road specifications are involved when creating projects for planning analysis, crash analysis, or other types of analysis. In addition, participation and coordination with national or Federal highway programs help to inform and improve network development connectivity.

Elements of NRN Development

To support State network improvements to meet National Road Network (NRN) goals, FHWA created a pilot grant program, the NRNP, focused on southeastern coastal States. These State road networks, frequently impacted by hurricanes, are often incorporated into disaster relief maps. The pilot grants support State exploration of ways to improve State road networks and create national road network connectivity.

Pilot Workflow

The NRNP includes seven States (and one district): Alabama, Delaware, District of Columbia, Florida, Georgia, Maryland, North Carolina, and Virginia. Each submitted a project statement and funding request to FHWA. Participating States were encouraged to formulate projects in support of one or more of the three NRN focus areas: network connectivity including interstate borders; intra-state borders, and topological connectivity of the network; spatial representation, including multi-carriageway roadways and intersections; and finally, spatial accuracy standards. State projects will continue through 2023, and FHWA will develop a summary of the collective State network improvements after the State work is complete.

Connection Points

To assist with state-to-state connectivity, FHWA partnered with the U.S. DOT Volpe National Transportation Systems Center (Volpe) to create a set of match points where ARNOLD routes cross State borders. The Volpe team used automated processes to align a State network to create these points. Points were shared with NRNP States in a spatial feature set that also included roadways near State borders, roads at or along borders, and demarcation of roads at each side of a match point. As part of the NRN project, where necessary FHWA will establish an adjudication process to support State adjustments of these match points.

Looking Forward

FHWA’s ARNOLD geometry checks address a variety of common errors including duplicate features and vertices, non-monotonic measures, spikes and kickbacks, overlaps, self-intersection, duplicate routes IDs, and non-simple features. ARNOLD-based products, however, continue to demonstrate inconsistency for national network applications. Through the NRN and NRNP, FHWA is taking steps to implement a workflow to improve national networks based on HPMS data. State-to-state connectivity for all roads will require regular State partnerships, and national-level coordination. The NRN program and improved ARNOLD data quality and completeness assist with network connectivity, and will lay the foundation for more consistent and widely used FHWA networks in the future.

1 See the FHWA GIS in Transportation website for details: https://gis.fhwa.dot.gov/.

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