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Cellular V2X Gets The Green Light

Have you ever been in a hurry and wished that all the traffic lights would turn green as you approach?

In the city of Alpharetta, Georgia, U.S. where I live - emergency vehicles equipped with a V2X onboard device can change a traffic light from red to green to allow the vehicle to pass through. Back in 2019, Alpharetta deployed V2X technology to 150 lights in their downtown that allows cars and traffic signals to communicate with each other, pedestrians, cyclists and other infrastructure. It eliminates the need for navigating through red lights and intersections filled with cars, pedestrians, and cyclists - saving emergency vehicles an estimated 10-12 seconds per intersection.

V2X in the U.S., EU, and China

V2X is an old-new technology. It has been on the drawing board for the last 20 years; the IEEE first published the specification of Wi-Fi-based V2X in 2010. And despite its promise of improved vehicle and road safety, the V2X market has struggled to take off due to a lack of spectrum regulations - compounded by a lack of interoperability and certification tests. This proved to be an opportunity for a competing cellular-based technology, C-V2X, supported by member companies of the industry association 5GAA, to gain a foothold.

In the U.S. in November 2020, the FCC approved a rule change that allowed 45MHz of the V2X communication band to be opened for unlicensed (Wi-Fi) use - which resulted in great dismay in the Automotive community. More recently, in March 2021 the U.S. Department of Transportation issued a Sources Sought Notice for any organizations capable of providing services, resources, facilities for testing emerging and future 5G NR technologies for V2X applications.

In the EU, initial momentum was for DSRC, which shifted somewhat in July 2019 to C-V2X as twenty-one EU countries voted against a European Commission plan (Delegated Act) to mandate Wi-Fi-based V2X. Today the EU is working on a co-existence model with several trials supporting both ITS-G5 and C-V2X under way.

China has been leading the way in V2X. After issuing the Smart Vehicles Innovation Development Strategy in February 2020, China started producing smart vehicles equipped with C-V2X technology. 90 cities have partnered with network operators to deploy roadside units for intelligent highways and urban roads. C-V2X is expected to be included in half of new cars in China by 2025, at which time China also plans to begin testing 5G NR-V2X technology. To drive collaboration across the industry ecosystem - The China Society of Automotive Engineers (C-SAE) hosts an annual event to promote interoperability testing among auto OEMs, chipset and module vendors, and application developers. In addition, the China New Car Assessment Program (C-NCAP) which evaluates vehicles for safety - plans to introduce C-V2X as part of its rating system by 2024.

Is V2X even necessary?

Developing advanced Line-of-Sight (LOS) sensors such as radar, lidar, camera, ultrasound is an ongoing process, but automakers are realizing they need a complementary Non-Line-of-Sight (NLOS) sensor suite in order to move beyond Level 2  driving in more places, including urban environments.

V2X provides see-through, 360-degree, NLOS sensing in all weather conditions to enhance the functionality and safety of autonomous driving – as shown in the figure. Whereas LOS sensors cannot indicate driver intent, V2X conveys intent by sharing sensor data - resulting in a higher level of predictability in situations such as road hazards or sudden lane changes. V2X improves situational awareness by offering soft safety alerts such as slower or variable speeds ahead.

Three applications of V2X

V2V links support a range of use cases such as blind spot, lane change, do not pass, road work, and vulnerable road user warnings, emergency brake lights, intersection movement assist, and follow‐me information for vehicle platooning and towing.

What happens if only a few vehicles have V2X technology?

For V2X to really work it needs to be wide-scale and it is only truly effective if the take-up level is high (some suggest over 97%). While it could be mandated that all new vehicles should be furnished with V2X technology, there is still the challenge of installing V2X in the 2 billion existing vehicles on the road.

Something to keep in mind though is that even at low industry penetration, V2X helps to reduce the time spent in traffic jams, and increases average speed through a traffic jam – because of more coordinated driving.

V2X Predictions

  • The next two decades will be very different from the last two for connected vehicles. Though technology can come top-down through government mandates and regulations - sometimes it comes bottom-up, and that is what we will see with C-V2X as automakers, consortiums, municipalities and cities play a significant role in driving adoption.
  • China’s moves in C-V2X and corresponding geo-political competition will act as a catalyst to move the U.S. and EU towards speeding up their own V2X strategies and deployments.
  • In the absence of regulatory consensus, we will see a coexistence model of both V2X standards in the initial years especially in Europe.
  • V2I will be the first ubiquitous application with use cases for emergency vehicles, public safety, school buses, and traffic flow. V2N will eventually be used to access information in the cloud, including real-time traffic, sensor, and high-definition mapping data.


In the early days of the automobile, navigating roadways was a chaotic experience, with pedestrians, bicycles, horses and streetcars all competing with cars for right of way. On August 5, 1914, American Traffic Signal Company installed the first traffic light at the corner of Euclid Avenue and East 105th Street in Cleveland, Ohio. Traffic signal preemption control by police and fire personnel was accomplished by an early system called RELCO (Radio Emergency Light Control) invented in Erie, Pennsylvania and later marketed as “Rad-O-Lite.” It used a radio transmitter in emergency vehicles to transmit one of two signals — the first signal caused traffic lights to “go green” in the North/South direction. The second signal caused traffic lights to “go green” in the East/West Direction. When active, the signal also caused a white light mounted on the traffic light to flash, indicating that the system was in-use and requesting traffic to clear the “emergency lanes.”

There were problems with Rad-O-Light: first, the system used very low power to prevent activation of lights on parallel streets. This made the range spotty and you could not guarantee the receiver would reliably work until you were almost into the intersection. Second, the system was poorly maintained: some lights would never activate, others would “trip” anytime somebody used a mobile radio nearby. Third, in the case of streets that did not follow a particular direction – it was random as to whether to use the North/South signal or the East/West signal. Finally, the flashing white lights on the traffic signals confused the motoring public.

There  should be no confusion for the residents of Alpharetta, Georgia with the technology their city has deployed. C-V2X will be a leading factor in improving vehicle safety, and reducing fatalities and injuries on their roads.

For further information on C-V2X design and test, go to: