Edge Computing Is So Fun - Part 2: The Future Begins with The Road Side Unitby@desmond-yuen
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Edge Computing Is So Fun - Part 2: The Future Begins with The Road Side Unit

by Desmond YuenSeptember 28th, 2020
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This is the second in a series of articles on edge computing, delving into the infrastructure of outdoor edge computing, the emergence of the Roadside Unit as a common building block, a real-life example of the Roadside Unit, and the way forward.

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Part 2: The Future  Begins with The Road Side Unit
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This is the second in a series of articles on edge computing, delving into the infrastructure of outdoor edge computing, the emergence of the Roadside Unit as a common building block, a real-life example of the Roadside Unit, and the way forward.

You can read part 1 here.

You probably walk past it or drive past it every day. But it is inconspicuous for most people. And it is evolving and becoming more intelligent. More importantly, it is becoming the common building block for outdoor edge computing applications ranging from smart city, traffic management, and V2X (Vehicle To Everything) for self-driving vehicles, etc. It is called the Road Side Unit (RSU.)

Overview of the Roadside Unit 

What is an RSU? From an Intelligent Transportation Systems (ITS) perspective, it is generally described as vehicular communication systems. The original definition of RSU was established by the Federal Communications Commission (FCC) as part of the allocation of the 5.9 GHz band for ITS. Please see below.

“Road Side Unit (RSU). A Roadside Unit is a DSRC (Dedicated Short Range Communications) transceiver that is mounted along a road or pedestrian passageway. An RSU may also be mounted on a vehicle or is hand-carried, but it may only operate when the vehicle or hand-carried unit is stationary. Furthermore, an RSU operating under this part is restricted to the location where it is licensed to operate. However, portable or hand-held RSUs are permitted to operate where they do not interfere with a site-licensed operation. An RSU broadcasts data to OBUs (Onboard Units)or exchanges data with OBUs in its communications zone. An RSU also provides channel assignments and operating instructions to OBUs in its communications zone, when required.”

Figure 2. Building blocks of a Roadside Unit. Source: US Department of Transportation (USDOT)

Figure 2 above shows the building blocks of an RSU. Typically, this is what we will find inside the RSU. It includes a processor that runs the applications, data storage such as memory, and communications capabilities such as 4G/LTE or 5G and GPS receiver that support secure communications with passing vehicles, other field equipment, and centers.

Beyond Traffic

In addition to the traffic management, the communication capabilities of the roadside unit make it a perfect choice for a lot of applications such as automatic toll collection, connected or automated vehicles, weather warnings, and smart cities, etc.

Here is an example of how RSU can help to reduce gas emission and fuel consumption. As you’re approaching a traffic light, have you ever wonder how long the light will last? Should you slow down, stop, or speed up? Sounds familiar?

This video shows a test of eco signal operations at UC Berkeley’s Richmond Field Station. The signal phase and timing information of a traffic signal is communicated to a vehicle over a 4G/LTE network link. Based on the vehicle’s engine and gear maps, an optimal speed trajectory is calculated by an advanced traffic signal control algorithm that allows the vehicle to pass an intersection with minimal fuel consumption. Source: Turner-Fairbank Highway Research Center (TFHRC)

With RSU, signal timing, and intersection location data can be obtained using connected vehicle technologies such as 5.9 gigahertz DSRC wireless communication, a global positioning system, SPaT (Signal Phase and Timing), and onboard equipment in the vehicle.

As the vehicle approached the intelligent intersection, the onboard computer received SPaT and GID (Geometric Intersection Description) information from RSU connected to the signal. The computer interpreted the data and performed velocity planning, sending a message to the display device, which informed the driver the light would change to green and suggested a safe speed for approach and departure legs at the intersection.

Using connected vehicle technologies, researchers at FHWA’s Turner-Fairbank Highway Research Center (TFHRC) were able to reduce emissions and fuel consumption. This savings is based on the energy a vehicle can save by driving through green lights without stopping which means burning less fuel and reducing emissions. Based on their experiments, they see a reduction of harmful emissions by about 12 percent and fuel savings between 10 and 20 percent.

Reducing emissions is just one of the many possibilities with the Roadside Unit. How do we get more of these applications from experiments to the market faster? 

Accelerating Roadside Unit Deployment

What is the biggest challenge when it comes to deploying roadside units? New York City is one of three Connected Vehicle (CV) pilot deployment sites selected by USDOT (U.S. Department of Transportation) to demonstrate the benefits of Connected Vehicle technology. The program started back in September 2015. As you can see from Figure 3 below, it is a three-phase, 75-month program. In other words, it took almost five years to get it up and running. 

Figure 3. Timeline for the New York City Connected Vehicles Project. Source: (

There is always a steep learning curve when new technologies are introduced and tested. Surprisingly, the biggest challenge for deploying more RSUs is not technology. In a survey conducted by the USDOT back on September 19, 2019, sixty percent of respondents cited “Funding” as the biggest challenge in deploying ITS technologies. Please see below.

Figure 4. Funding is the biggest challenge for deploying more RSUs. Source: US Department of Transporation

When it comes to funding, it is not just the upfront cost to purchase and deploy the roadside unit. The ongoing operations and maintenance also cost money. Many of the local governments might have funding to get started but they do not have the funding to cover the recurring costs. 

To start with, the cost per device varies depending on what is inside the box. I have seen numbers ranging from $1,300 to $18,000 and it does not cover the cost of deployment. The on-going operations and maintenance can cost $2,000 to $3,000 a year. Below is an example from the Georgia Department of Transportation on how much it costs per device and the deployment cost for their connected vehicles project. Again the cost will vary depending on location, usage, and what is inside the roadside unit. For example, it will probably cost more to deploy and maintain a roadside unit in a metropolitan area like New York City.  

Figure 5. Capital cost and associated costs in deploying and maintaining an RSU. Source: Georgia Department of Transporation (

How do we address the funding challenge? Assuming that funding from the government is limited, getting a new source of income from the service offered by the RSU will help cover some of the costs. For example, if the RSU is being used for automatic toll collection, part of the toll fees collected can be used to cover the operating and maintenance costs. 

In addition to lowering the cost of the RSU, increasing the capability of the RSU to handle more functions and devices will reduce the number of RSUs required.

The Remaking of The Roadside Unit

For the RSU to support more functions, it has to support a broader set of hardware devices than just being a communication device. To get a glimpse of the future of the Roadside Unit, let’s look at the testbed at the Antwerp Smart Highway test site.

Figure 6. What is inside the RSU at the Antwerp Smart Highway test site? Source: Federation For Fire Plus

The Road Side Units are deployed along the E313 highway in Antwerp (located in Belgium) on top of the gantries (a bridge-like overhead structure with a platform supporting equipment.) On top of the RSU are the antennas for the communication modules. See Figure 6 above.

Figure 7. Block diagram of the RSU. Source: Federation For Fire Plus

Each RSU consists of a large electrical cabinet that houses all the different modules of the RSU. See Figure 7. These include modules for wireless communication, modules for local processing on the RSU, and modules for remote management (reduce field service operating costs.) The hardware and communication modules inside the RSU provides support for V2X radio links, such as short-range based on ITS-G5 and C-V2X with PC5 interface working on 5.9 GHz. Vehicles equipped with the V2X will be able to receive information from the RSU. And the long-range communication is based on 4G. The modular design approach of the RSU has increases the serviceability as well as making it easy to add new capabilities to the box.

One thing to note here is that the RSU is using a Supermicro Mini 1U Rackmount Server to do the local processing. See Figure 8. Instead of sending data back to the data center, the processing of data can be done locally. In addition to getting faster results, it’ll also save on backhaul communication costs.

Figure 8. Mini 1U Rackmount Server from Supermicro

The PICe slots inside the rackmount server will allow the end customers to support more devices such as network cards and VPU (Vision Processing Unit) cards etc. A good example is traffic cameras. By bringing more VPU cards into a single server to support more cameras, it’ll reduce the number of servers required to process the data from the traffic cameras, etc. As a result, the infrastructure cost as well as installation and maintenance costs will be lowered.

Way Forward

Roadside units (RSUs) have a crucial role in the future of the global economy. Yes, infrastructure takes time to build. However, there are so many pressing issues we are trying to resolve e.g. traffic congestion, pollution and climate change, etc. Beyond the funding issue, security and standard are the biggest challenges. To go beyond the proof of concept and scale, businesses and governments around the world need to work together to resolve these challenges.

If you have any ideas and suggestions on how to accelerate the deployment of the Roadside Unit, please share them by leaving a comment.


1. The Intelligent Transportation Systems Joint Program Office has a wealth of information and training materials. 

Intelligent Transportation Systems - Joint Program Office Home Page
The Office of the Secretary of Transportation (OST-R) is dedicated solely to the advancement of the U.S. Department of…

2. Emission Reductions, Fuel Savings Demonstrated At Turner-Fairbank

Emission Reductions, Fuel Savings Demonstrated At Turner-Fairbank
TFHRC’s intelligent intersection delivers SPaT and GID data to a test vehicle equipped with a DSRC modem, computer…

3. The webpage has an excellent summary of the Smart Highway Testbed at Antwerp and a good overview of the implementation of an end-to-end solution.

Smart Highway
The Smart Highway testbed is designed for vehicle-to-everything (V2X) communication research. The Antwerp Smart Highway…