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How Connected Vehicles Work

In 2018, more than 37,000 people were killed needlessly in traffic crashes. In addition to the devastating human toll and suffering from motor vehicle crashes, the American taxpayer supports more than $140 billion per year in costs for emergency response, fatalities, injuries, and property damage related costs. For more than a decade, the U.S. Department of Transportation has been steadfastly researching, testing, and demonstrating technologies that can reduce these staggering numbers.

Intelligent transportation systems (ITS) that use cooperative dedicated, short-range spectrum (also known as vehicle-to-everything or V2X communications) provide the potential to prevent a significant number of crashes and enhance the safety of our nation’s transportation system. When integrated into a vehicle (cars, buses, trucks, bicycles, motorcycles, wheelchairs, etc.) or into infrastructure, this V2X communication capability offers a powerful 360-degree sensor of threats and hazards along our roadways. It is a tremendous break-through innovation that has the potential to move our society toward zero crashes. 

The Connected Vehicle concept

Connected Vehicle (CV) technologies are equipment, applications, or systems that use V2X communications to address safety, system efficiency, or mobility on our roadways. The CV concept uses data from short-range communication broadcasts and peer-to-peer exchanges within approximately 300 meters to “sense” what other travelers (vehicles, bicyclists, pedestrians, wheelchairs, motorcycles, buses, trucks, and others) are doing and identify potential hazards.

Vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) devices communicate via radio signals, which are omni-directional (i.e., offer 360 degrees of coverage). This allows two equipped vehicles to “see” each other and exchange critical information—regardless of whether the vehicles are in view, around a corner, or behind a building or cornfield. In comparison, a vehicle that only relies on line-of-sight sensors is unable to detect the presence of another vehicle that is not directly visible, let alone determine the other vehicle’s heading, speed, movement-related information, or operational status. 

V2X communications enable vehicle- and infrastructure-based devices to constantly monitor this data within a short range, providing time to warn travelers to act before an accident occurs. V2X exchanges are non-networked and have the ability to provide very fast (known as “low latency”) communications. They also create an “ad hoc” environment as vehicles, pedestrians, bicyclists and other travelers—including those out of line-of-sight—move into and out of exchanges in a dynamic and rapidly moving environment. 

V2X communications also offer security—each message is trustworthy through immediate authentication that includes privacy protection. Interoperability is the foundation of these capabilities. Without the system as a whole being interoperable and free from interference, the CV environment degrades and breaks down. As a result, the V2X applications cannot deliver the tremendous public safety, system efficiency, and mobility benefits. Further, there is a strong expectation that V2X communications can enhance the integration of automated vehicles into our current fleet of non-automated vehicles and continue to prevent crashes.

How the 5.9 GHz band plan for cooperative ITS works

In 1999, the FCC allocated the spectrum for transportation safety from 5850 MHz to 5925 MHz as an application within the mobile service. In 2006, the FCC provided the transportation community with service rules that established a band plan with specific designated channels. 

According to the rules, safety-of-life communications have the highest priority and public safety communications have the second highest priority through* two separate channels designations—one channel for crash avoidance V2X and one for public safety V2X which uses higher-power for those times when public safety and emergency response must silence or suppress nearby communications to provide priority. A 5 MHz reserve band protects the Safety Band from spectrum interference from unlicensed Wi-Fi devices operating below the band. The reserve band absorbs the energy from those unlicensed devices. The remaining channels are used by other types of safety (for instance, road-weather warnings), system efficiency (for instance, security downloads or field-data uploads to traffic management centers), and mobility (for instance, freight logistics or congestion management) applications that can tolerate a small amount of interference or that can wait an extra millisecond to transmit.

Dedicated spectrum enables V2X communications to adjust for dynamic situations

V2X applications use the spectrum in a dynamic fashion for several reasons including:

  • V2X devices can adjust their power levels and/or data rates when accidents are forming to send more frequent messages to those vehicles that could potentially be involved in a crash.
  • V2X devices can adjust based on spectrum congestion in dense urban areas.
  • V2X use is not as dense in rural areas but addresses more devastating crash types as well as facilitates faster and safer emergency response in rural areas.
  • V2X applications have a wide range of message sizes; V2X safety algorithms are adjusted for different vehicle heights and weights (such as motorcycles, pedestrians in wheelchairs, etc.).
  • Traffic conditions vary widely on a moment-to-moment basis, particularly in inclement weather.


Technology evolution and a technology-neutral (but not outcome-neutral) stance

The U.S. DOT is actively engaged in supporting deployment of V2X communication technologies that will provide tremendous safety and efficiency benefits. Because transportation communications technologies continue to improve, the U.S. DOT also continues performance testing of new communications technologies—for instance, the newly emerging 5G technologies. However, U.S. DOT rigorously tests new forms of V2X communications and devices from a safety perspective to assure that their use does not result in unintended consequences or raise the risk for crashes.

V2X applications have been piloted and tested, have proven to be interoperable, and are now operational in regions and states throughout the country. Federal, state, and local governments have invested more than $2 billion deploying this life-saving technology. Now, the United States stands at the brink of a historic opportunity to implement these interoperable and cooperative capabilities in a manner that is available to all travelers.

[*] 47 C.F.R. § 90.377 (d).