FRS vehicle preference using V2X

FRS vehicle preference using V2X

Pic. no.1: Fire engine with preference.

Pic. no.1: Fire engine with preference.

This article describes the ongoing project of testing absolute preference of vehicles of the Fire Rescue Service (FRS) in Brno. The other participants of the project are the Fire Rescue Service,  Brněnské komunikace, and the Patriot company. The project includes 5 intersections and 2 vehicles. Our communication unit UCU 5.0 equipped with a two channel V2X module is the basis of the project. By using the international V2X standard the project brings a completely original solution. This is the very first installation of such a system in the CR.

Why V2X communication

Pic. no.  2: V2X communication principle. Source:

Pic. no. 2: V2X communication principle. Source:

The FRS vehicle preference is based on the new unifies European standard of communication vehicle-vehicle and vehicle-infrastructure, known as V2X (vehicle-to-everything, or C2X, C2C – car-to-car). This is a standard which will be used by all vehicles manufactured in the future (e.g. Volkswagen has been planning to use this in vehicles since 2019). This is a unification of all communication among vehicles and between vehicles and infrastructure including intersection controllers.

As it is highly probable that this communication will be mandatory for all traffic participants in the near future, using it for communication with infrastructure is a logical and sustainable choice independent of any supplier.

In our system, V2X communication is used for direct and independent communication with intersections. Its range is 300 meters in a built-up area and more than 1 km in open landscape (verified during the project). A vehicle sends information about its state periodically up to 10 times per second (the frequency changes dynamically depending on the utilization rate of the V2X channel). An intersection controller communicates in a similar way, it can inform its surroundings about e.g. the state of its signal plan.

Lower signal spread in built-up ares given by the 5,9 Ghz frequency is one of the disadvantages of the V2X communication. The communication unit must be placed on an elevated spot ideally in the middle of an intersection. The typical spot is a traffic light pole. Such a placement provides good coverage of all the intersection arrival directions.

The general goal of vehicle to vehicle and vehicle to infrastructure communication is to increase traffic safety and efficiency. Radio information transmits the state of a vehicle into its surroundings much faster than the sensor systems of surrounding vehicles can detect and evaluate. The advantages include:

  • FRS vehicles inform the surrounding vehicles about their passage
  • coordination of the transport route infrastructure with infrastructure,
  • possibility of a warning against a collision of two vehicles going in sequence
  • communication not affected by weather (fog)

and many more advantages.

FRS vehicle preference principle

Pic. no. 3: Example of absolute vehicle preference.

Pic. no. 3: Example of absolute vehicle preference.

Vehicle preference is based on a vehicle position obtained from GPS (or other navigation systems such as Galileo and Glonass). When a vehicle arrives to a defined area surrounding an intersection, it can request preference. The preference request is either sent by an on-board computer or it is connected with the state of one-bit inputs e.g. activation an FRS vehicle flashing light. The final decision whether and when preference will be granted is made by the controller or the controller communication unit. The intersection itself makes the decision when to initiate a change of the signal plan. The green light is set only in the direction of the arrival of an FRS vehicle to „clear“ the intersection or at least make it possible to go in the direction of the oncoming traffic.

Communication of a vehicle with an intersection controller must contain these units:

  • vehicle communication unit (UCU 5.0) functioning as OBU – on board unit,
  • intersection communication unit (UCU 5.0) functioning as RSU – Road side unit,

Preference decision

Pic. no. 4: Example of defined preference corridors.

Pic. no. 4: Example of defined preference corridors.

As stated, vehicle preference is decided based on the vehicle position. This position is evaluated according to parameters given for a specific intersection. The designated area is defined in intersection configuration. Preference works on the basis of:

  • current vehicle position,
  • areas marked on a map,
  • direction of the drive,
  • flashing light is on.

Each intersection arrival direction has its own defined area (polygon) where priority is activated – green color in Picture 4. The area is long enough for the controller to change the signal plan and set the required signal in the given direction. Preference is activated at the arrival to the area. If the vehicle leaves the area the preference is terminated. The red area in Pic. 4 is an exit polygon. When it is passed through, it is assumed that the vehicle has gone successfully through the intersection and that the priority request is finished.

Polygons are a more robust and universal version of the well known MPT vehicle sign-in and sign-out points. These points are defined for vehicles while polygons are defined for intersections. Giving the decision logic to an intersection has the advantage of the intersection knowing the situation in the surroundings much better than an oncoming vehicle. Thanks to more frequent communication with vehicles, controllers have much better vehicle position information, they do not have to rely on just one point and can better determine when to initiate preference.

Communication between a vehicle and an intersection

Pic. no. 6: Principle of preference.

Pic. no. 6: Principle of preference.

Our system is designed to use a unified way of solving preference of both ES and PT (both municipal and regional PT). The behavior is different for each of these vehicle types, but the technology is the same, and the same international standard is used. Our idea was to create a system where it is possible to use just one communication unit for a controller for all purposes.

The system is based on a combination of two communication interfaces: short range V2X and standard mobile connection using the LTE standard. The roles and features of the interfaces are as follows:

  • LTE – mobile connection to inform an intersection in time – it is slower, less reliable, but it works whatever the distance – has a long range. It is used to inform that a vehicle is arriving to an intersection. It also takes care of remote monitoring and unit administration
  • V2X (C2X) – independent, direct, medium range communication as per the international standard, but its range is shorter.

Using 2 communication interfaces for one type of communication makes the system more robust and reliable. When one communication type is broken/switched off the other one keeps working. This is a significant advantage. Moreover, using a mobile internet connection will be necessary due to security certificate updates (see below).

Securing the communication against misuse

Pic. no. 7: Vehicle preference message security.

Pic. no. 7: Vehicle preference message security.

Every vehicle periodically broadcasts its base state (position, speed, acceleration, direction, etc.) and its vehicle type and purpose – for example „FRS vehicle in action“ or „public transportation vehicle“. This typically happens every 100 ms. CAM (Cooperative Awareness Message) messages are used. These messages are received by all vehicles and infrastructure components in the surroundings and they can react to them – for example warn drivers about an imminent FRS vehicle passage, or about a possible collision with another vehicle, etc. Moreover, as stated, it is possible to use a different message to inform drivers about preference requests.

Misuse of this information (offers itself in the case of vehicle preference) is prevented by adding high level security that cannot be reached in standard radio communication. Security is an essential component of the V2x communication. Messages sent by vehicles are digitally signed and intersections „enable preference“ only for vehicles that signed „correctly“. Signature keys are stored in a HW module so it is not possible to get to them and to hack the system.

This provides:

  • high security rate using authorization and authentication methods,
  • every message is signed and sent together with a certificate authorizing the sending of the message. Here the intersection operator would be the certificate issuer.

Vehicle and intersection solution

Currently, prototypes of  unit UCU 5.0-V2X are in use that have general properties for verifying many possible functions. This unit is placed on a vehicle roof and on traffic lights. Units assembled this way provide V2X communication range of up to 1000 m at direct visibility. The RS 485 interface is used to communicate with intersection controllers.

Pic. no. 8: Prototypes of V2X units based on UCU 5.0 – on the left – outer unit placed on traffic lights, and  on the right – a unit placed on a fire engine.

Pic. no. 8: Prototypes of V2X units based on UCU 5.0 – on the left – outer unit placed on traffic lights, and on the right – a unit placed on a fire engine.

Conclusion and who wrote about the project

We see this solution as a very perspective one, it is based on the existing ETSI – G5 norms, i.e. this is a solution applicable to whole Europe. The advantages are the communication speed and the near impossibility of misuse ensured by digital communication signatures. The high performance UCU 5.0 units allow cameras to be connected to the system. For example the FRS dispatching now receives camera streams from vehicles going to a place of intervention or streams from the place of the intervention itself. The system can also include public transportation and thus provide multipriority preference of FRS vehicles, ambulances, , and public transportation (MPR and RPT). This means that for example an FRS vehicle will have  absolute priority followed by an ambulance, then e.g. trams and after that other public transportation vehicles as it is now.

During this project we want to continue testing setting of preferences at intersections for ambulances.

Example of test drives of an FRS vehicle with absolute preference on 16.11.2017 (taken from the FRS web):

Wrote about the project:

  • Brno Fire Rescue Service web page -  here:
  • in Blesk here
  • the information was also presented by ČT and in the South Moravia insert of Právo