  This report aims to support the Tennessee Department of Transportation's
decisions about vehicle and infrastructure communication technologies. The
transition from Dedicated Short-Range communication (DSRC) V2X to Cellular
Vehicle to Everything (C-V2X) is explored using USDOT guidance on relevant
issues and presenting the results of experimentation in Tennessee and the
potential pros and cons. DSRC V2X technology has been planned at traffic signal
in Tennessee, e.g., 152 Roadside Units (RSUs) were planned by TDOT using DSRC
V2X and Bluetooth combination units in the I-24 smart corridor. Similarly, many
pilot programs and testbeds around the nation have deployed DSRC V2X technology
and are now impacted by the Federal Communication Commission's (FCC) ruling on
opening safety band. The implication is that DSRC V2X deployments (and future
deployments) should migrate to C-V2X. Notably, dual-mode RSUs are available
along with LTE C-V2X. The transition can be done by working with vendors, but
surely this involves more than swapping DSRC V2X devices with LTE C-V2X
devices. Complicating the migration to C-V2X is TDOT's role in traffic signal
operations and maintenance, which is limited to funding and
designing/construction of traffic signals, but local agencies operate and
maintain signals. Hence, local agencies will work with TDOT to operate and
maintain C-V2X technology. Moreover, C-V2X technologies are not widely
tested-interference by unlicensed devices and channel congestion can adversely
affect safety-critical applications. Given the substantial uncertainties in
transitioning to these technologies, TDOT's discussion with IOOs about the
operation and maintenance of C-V2X may have to wait for the resolution issues,
while TDOT can invest in experimentation with dual-mode devices.
Recommendations are provided about dual-mode devices, CAV data, and needed
research and testing.

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