BACKGROUND

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ideal for last-mile communications connectivity where cellular or optical fiber is unavailable or other architecture is outdated.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.

The Federal Communications Commission’s current licensing freeze, while it considers new rules for the 4.9 GHz spectrum band, leaves a limited number of options for new use of the band. While it is not presently known when the freeze will be lifted, and if any new rules will be put into effect, there are nevertheless currently several potential opportunities for state department of transportation operations in the band.

NCHRP Web-Only Document 422: Planning for 4.9 GHz Spectrum Changes, from TRB's National Cooperative Highway Research Program, provides background and guidance for transportation agencies that wish to implement systems in the band.

Publication Info

16 pages |  8.5 x 11 |  DOI: https://doi.org/10.17226/29256