The National Academies

NCHRP 23-28 [Active]

Planning for 4.9 GHz Spectrum Changes — What Transportation Agencies Need to Know

  Project Data
Funds: $250,000
Staff Responsibility: Mike Brooks
Research Agency: Blue Wing Services
Principal Investigator: Alan Tilles
Effective Date: 9/23/2023
Completion Date: 1/22/2025
Comments: Research in progress


In 2002, the Federal Communications Commission (FCC) designated the 4.9 GHz (4940-4990 MHz) broadband spectrum for public safety use. This spectrum has proven to be ideally suited for point-to-point broadband microwave paths with a typical operations range of approximately 15 miles. It can be also operated in point-to-multipoint configuration making it ideal for last-mile communications connectivity where cellular or optical fiber is unavailable or other architecture is outdated.

Although radio communication is not a core function of state departments of transportation (DOTs), having ready access to the 4.9 GHz band supports many critical transportation functions. State DOTs use the 4.9 GHz band for various applications, including intelligent transportation systems (ITS), traffic incident management systems, variable message signs, road weather information systems, highway advisory radios, traffic signal control, public safety dispatch, and closed-circuit television cameras. During emergencies and disasters, when cellular carrier services become over subscribed, the 4.9 GHz band gives state DOTs and other public sector agencies a reliable communications option that supports effective response. The 4.9 GHz band is also used to support safety-critical Vehicle-to-Infrastructure (V2I) communications for connected and automated vehicle (CAV) implementation. Looking to the future, some have suggested that the 4.9 GHz spectrum may play a role in detection and avoidance for Advanced Air Mobility and unmanned aerial vehicles. Many state DOTs use the 4.9 GHz spectrum, either through licenses they directly hold or under licenses held by other agencies in their state. Because the spectrum is a valuable resource for transportation-related communications, the number of state DOTs interested in using the spectrum may increase.

In 2020, the FCC adopted a rule that allowed for expanded use of the 4.9 GHz band by commercial entities and proposed new, state-level licensing and coordination of operations (WP Docket No. 07-100). The expansion is anticipated to lead to curtailed availability of the 4.9 GHz band for state DOTs and other public agencies and require them to revisit plans and projects that include the use of the band. In 2021, the FCC issued a “stay” order for this rule change followed by a Further Notice of Proposed Rulemaking (FNPRM) to seek comment on a range of issues, including allowing private sector entities to use the band; identifying an entity responsible for the administration of licenses; interference protection; shared use via leasing arrangements; and other regulatory and policy topics. Although what specific actions the FCC may take is uncertain, future FCC action is anticipated. The changes currently under consideration will significantly affect the availability and cost of using the spectrum, how licenses will be secured, how interference on the spectrum will be minimized and mitigated, and how and whether state DOTs will be able to continue to use the 4.9 GHz spectrum for public safety purposes.

Research is needed to evaluate anticipated regulatory changes to the 4.9 GHz spectrum so state DOTs are prepared to adapt and preserve the ability to continue essential communications for critical transportation functions.


The objectives of this research are to develop:

  • Plausible scenarios that describe how the spectrum might be managed;
  • A guide with strategies for state DOTs to align current and future projects, communications system processes, and programs to use the spectrum under each scenario; and
  • A portfolio of training and communications materials to support the implementation of the strategies and explain the value of the spectrum for transportation-related uses.  


Anticipated tasks include: 

  • Review recent FCC actions related to the 4.9 GHz spectrum;
  • Summarize current and anticipated use of the 4.9 spectrum by state DOTs. Information sources may include published reports, previous surveys of state DOTs, and the FCC Universal Licensing System;  
  • Through targeted outreach, collect information on concerns, priorities, interests, and information gaps related to current and future use of the 4.9 GHz spectrum from:
    • Staff responsible for managing state DOT communications systems, including state DOTs that may have limited experience in using the 4.9 GHz spectrum;
    • State Statewide Interoperability Coordinators (SWICs);
    • Current users (e.g., law enforcement, state emergency managers);
    • Potential new users (either as license holders or through shared use agreements); and
    • Other partners and stakeholders in the current and future governance and use of the spectrum.
  • Develop at least four plausible scenarios for licensing and allocation of the 4.9 GHz spectrum. Scenarios should include conditions that will accommodate, constrain, and/or severely reduce state DOT use of the spectrum. Potential scenarios include:  
    • Designation of a statewide band manager with all or most of the spectrum reserved for public safety use under a new licensing program;
    • Designation of a statewide band manager with an auction of part of the spectrum;
    • Establishment of a national band manager with all or most of the spectrum reserved for public safety use under a new licensing program; and
    • Establishment of a national band manager and an auction of licenses for most of the spectrum.
  • Refine the scenarios based on the NCHRP review;
  • Identify key characteristics that affect state DOT actions and opportunities under each scenario, including:
    • Existing governance of public safety shared or interoperable communications (e.g., formal/informal agreements or statutes);
    • Level of expected competition for the 4.9 GHz spectrum (licensed, unlicensed, broadband, 5G);
    • Potential for interference and how interference could be mitigated;
    • Current and planned use of the spectrum;
    • Extent of feasible alternatives for state DOTs (e.g., optical fiber, cellular);
    • Anticipated cost implications for licensing, leasing, and equipment; and
    • State DOT experience and capacity in spectrum management.
  • Evaluate the potential impacts on state DOTs for each scenario;
  • For each scenario, develop strategies and guidelines for advancing current and anticipated state DOT communications needs that address:
    • Implications of the licensing program and the designation of the band manager;
    • Communicating state DOT needs and priorities to a licensing entity;
    • Partnering with other state agencies for shared use, licensing, and other issues;
    • The degree of competition within the spectrum;
    • Ensuring interoperability between states and between states and regional jurisdictions;
    • Managing interference and unlicensed users;
    • The potential for channel plans to avoid interference between shared spectrum and co-located spectrum users;
    • Feasible alternatives to the 4.9 GHz spectrum (e.g., other licensed and unlicensed shared spectrum, commercial carrier offerings, leasing other radio spectrum);
    • Cost implications for the state DOT;
    • Needed process improvements, resources, and staff capacity to implement the strategies; and
    • Other state DOT needs, priorities, and considerations identified during the research.
  • Identify themes and concepts for communicating the research findings, scenarios, and strategies to state DOT leadership, communications systems staff, and other functional areas of the state DOT as well as to external partners and stakeholders.

The final deliverables will include:

  • A report with the following:
    • Documentation of the research activities;
    • Key findings;
    • Scenarios with state DOT strategies for each; and
    • Other topics identified during the project.
  • A portfolio of concise training and communications pieces for state DOT communications staff to use with internal and external audiences in understanding the implications of changes in the management of the 4.9 GHz spectrum, how to respond, and to evaluate agency readiness to respond. The content should be suitable for state DOTs with different levels of experience in using and managing the 4.9 GHz spectrum. The portfolio may include:
    • Downloadable, customizable materials in a file format readily used and modified by state DOT staff;
    • Brief videos; and
    • Infographics and graphic presentations. 


  • A stand-alone technical memorandum that identifies implementation pathways, key implementers of the results, and well-defined scopes of work for further dissemination and pilot implementation of the strategies. The technical memorandum should provide adequate detail about how state DOTs and other transportation agencies can implement the results of NCHRP Project 23-28.


STATUS: Active.

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