Cooperative ITS safety-related services are based on a connectionless mobile communication network work. Compared to traditional connected services known from smartphones they distinguish with respect to basic principles, characteristics, service classes and user groups as well as related business models. The CAR 2 CAR Communication Consortium publishes a set of frequently asked questions providing background information, explaining the main points of interest also covering the cooperative technologies, features and differences. By nature the FAQs are not complete and will be therefore updated from time to time.  

FAQs – Frequently asked Questions

 Do the different terms used for short-range communication and services in the C-ITS domain imply differences?Different communities and regions in the world use different terms for short-range communication and services with very similar meaning which sometimes might lead to confusion. In general, cooperative technology and functionality have to be distinguished. The core radio technology for ad-hoc short-range communication is specified by the IEEE 802.11p standard. In the USA, this technology is also called DSRC or WAVE. The European adaption is known as ETSI ITS G5 or WLANp. This technology is used to enable functionalities and cooperative services. Here you find terms like Car2X, V2X (V2C, V2I/I2V, V2N/N2V, V2P/P2V, ...) which can be usually summarised by cooperative V2X (vehicle to anything).  
 When will drivers benefit from cooperative V2X on European roads?The Day 1 cooperative V2X safety applications have been developed and standardised during the last decade. As of 2019 the first mass-market vehicles are equipped with cooperative V2X safety function as standard equipment. Further vehicle brands follow. As of 2020 European road operators offer the roadworks warning as one of the first services in daily operation complemented by a bundle of further infrastructure enabled Day 1 services. By this already first drivers benefit from cooperative V2X and service quality will improve steadily with increasing market penetration. 
 What are the advantages of cooperative V2X for drivers?Cooperative V2X is specially designed to improve road safety free of charge and by this supports assistance of drivers and automation of vehicles and road operation. In case of a danger ahead the driver will be warned by cooperative V2X in time and supported to avoid the critical situation. Volkswagen Golf 8 has received the Euro NCAP Advanced Award 2020 for the implemented Local Hazard Warning system that uses ad-hoc short-range communication ETSI ITS G5 between vehicles, and between the vehicles and its surroundings, to give drivers an early warning of safety hazards.
 What are the advantages of cooperative V2X for road operators?Road operators are in charge of managing traffic flow and of operating their road network and its maintenance. Beyond gantries, variable message signs and traffic lights cooperative V2X offers the opportunity to interact with cooperative vehicles to improve road safety and road capacity. By locally providing cooperative information road operators benefit from market driven improvements of driver assistance systems and automated driving functions of cooperative vehicles. Furthermore, cooperative vehicle data very much improves the statistical probe traffic information enabling further innovations for traffic management and maintenance of traffic, roads and bridges.
 Is cooperative V2X tamper-proof and takes care of the drivers’ privacy?For improving road safety local short-term tracking of the road users in the vicinity of the ego-vehicle is required. Privacy by design has been applied to the cooperative V2X systems for ensuring the privacy of the driver. All identifiers of the messages sent out change over time and travel phase following an optimised privacy strategy avoiding long-term tracking. Furthermore, the frequency and the amount of shared data is dynamically triggered by the driving situation following the principle of data economy. The cooperative V2X design also considers threat analysis for compromising and manipulating message sets and/or ITS stations. Consequently, all message sets are signed with an electronic signature avoiding manipulation, replay and misuse.
 Why are Day 1 message sets not encrypted?The Day 1 message sets like Cooperative Awareness Message (CAM) and Decentralised Environmental Notification Message (DENM) are safety related messages, which need to be understood and processed in real time by all other cooperative road participants in the vicinity of the sending vehicle. Due to this fact encryption of these messages would not provide any advantages on privacy, but needlessly waste computation power and by this delay well adapted safety measures in critical situations. Instead of encrypting messages, all message sets are signed by the sender and verified by the receiver. In this way it is ensured that all data is reliable and not susceptible to manipulation by third parties without the need for encryption / hiding the data.
 How do the Day 1 message sets look like?The most important standardised Day 1 message sets are called Cooperative Awareness Message (CAM) and Decentralised Environmental Notification Message (DENM) specified by [ETSI EN 302 637-2] and [ETSI EN 302 637-3]. The message sets consist of a header followed by the unencrypted payload, a signature and a certificate. The CAM payload consists of a basic container, high and low frequency containers and further optional containers. The DENM payload is formed by a management container, optional situation and location containers and further optional containers. Each of the containers might contain relevant data elements and further containers.
 Which are the most important common data elements of the C-ITS message sets?The header specifies the protocol version used, the message type and the stationID which results from the pseudonymous certificate used and changes over the time synchronised with the change of the pseudonymous certificate. 
The signature is a kind of checksum calculated based on the payload and the time stamp of the message. This enables the receiver to check whether the message is correct or has been manipulated and whether the message is valid or outdated / re-used.
The pseudonymous certificate enables the receiver of a message to check whether the sender is trustful authorised, and which assigned level of authorisation the sender has. 
 Which consequences on assisting road safety in Europe towards accident free traffic (vision zero) result from the absence of interoperability at radio link level between LTE-V2X (PC5) and IEEE 802.11p?The benefits of cooperative V2X services progressively increase with the penetration of interoperable implementations in vehicles and road infrastructure. A penetration of about 3% to 5% is seen as tipping point for receiving first benefits from cooperative V2X. Missing decisions are already leading do a delayed entry of C-ITS stations. This and possible non-interoperable implementations cause reduced harvesting of the big potential improving road safety and by this cost many lives which could have been protected. Furthermore, the absence of interoperability at radio link level between LTE-V2X (PC5) and IEEE 802.11p will - without any regulation - either split the market or multiply the costs, at least for manufactures, if they were to implement both options. A split market will result in a less effective safety system overall. Higher costs will most probably lead to a reduced implementation rate with the same result: a less effective safety system overall. 
 What are the special features of C-ITS compared to other ITS services?Cooperative Intelligent Transport Systems (C-ITS) refers to transport systems, where the cooperation between two or more ITS sub-systems (personal, vehicle, roadside and central) enables and provides an ITS service that offers better quality and an enhanced service level, compared to the same ITS service provided by only one of the ITS sub-systems.
 Which technologies enable C-ITS? Suitable technologies depend on the applications to be realised. Avoiding accidents by fore-sighted cooperative driving and safety applications are primarily a tactical issue requiring the sharing of information, perception, awareness and intentions between the road users in their vicinity and with the local road infrastructure. The cooperative V2X services based on ad-hoc short-range communication ETSI ITS G5 focus on this class of safety related applications. Applications like route planning and navigation focusing on the strategical and planning level as well as remote tele-driving require wide area communication. For covering all C-ITS applications a hybrid approach is required. Here the proven short-range communication ETSI ITS G5 can be complemented with other mature communications like cellular systems (3G, 4G, 5G) and broadcast systems (RDS-TMC, DAB+).
 Why does cooperative ad-hoc short-range communication require interoperability?In a cooperative traffic safety scenario, each sending vehicle has to share its information with all other vehicles and road participants in its vicinity in real-time. Fast and efficient communication is achieved by using local ad-hoc broadcast to all (unknown) receivers close by. For benefitting from the technical progress over the years newer vehicles might be equipped with C-ITS devices having implemented newer communication standards. In this case the C-ITS devices of the vehicles might have different capabilities in cooperative traffic safety scenarios. For ensuring that legacy C-ITS devices stay fully operational and can communication to new or other C-ITS devices either interoperability of the communication is required, or multiple transmissions of the same information are required for each of the non-interoperable communication standards. Due to the required multiple transmissions the latter option is less spectrum efficient and is therefore not advantageous as wasting allocated spectrum limits the potential for each of the cooperative communication technologies. 
 Which technical options exist to realise a hybrid C-ITS system?Hybrid C-ITS systems combine short-range radio technology like IEEE 802.11p WLANp or LTE-V2X PC5 with complementing wide-area radio technologies based on available public cellular networks (e.g. 3G, 4G, 5G) and other media like DAB. Use Cases have specific requirements resulting in the selection of using appropriate short-range and/or wide-area radio technologies for ensuring the required quality of service. 
Except for the physical layer all standards specifying the communication stack have to fulfil the technology neutrality requirement. This allows the design of a technology agnostic communication stack which can be used on top of the physical layer specifications which specify different radio technologies.
Hybrid C-ITS systems based on IEEE 802.11p WLANp and available 4G cellular communication are already being deployed and operated in the European market. Using the technology agnostic communication stack also the combination of LTE-V2X PC5 with available 4G cellular communication can be realised. For making use of the developments improving the radio technologies in future next step short-range IEEE NGV or 5G NR-V2X PC5 might be combined with 5G cellular. All hybrid C-ITS systems will most likely use the same cellular communication systems. Looking to the short-range communication the performance in the 5.9 GHz ITS spectrum is expected to be quite similar for the old and new radio generations of the competitive, but not interoperable technologies which distinguish mainly e.g. in their migration and evolution paths.
 Why is short-range communication well suited for improving road safety?Improving road safety targets on avoiding accidents between road participants. The probability of an accident strongly depends on the local traffic situation. Fore-sighted driving strategies considering the current local traffic situation in the vicinity of a vehicle are well suited to contribute to avoiding critical traffic situations and to take ad-hoc counteractions aiming on the avoidance of remaining potential accident risks. The quality of service of the connectionless short-range broadcast communication improves the closer the road participants approach each other and by this supports individual ad-hoc actions for mitigating the local critical traffic situations. Furthermore, this physical principal of short-range communication ensures functioning anywhere at any time where cooperative road participants come closer to each other avoiding any local dead spot.
 How does cooperative automated driving benefit from C-ITS?For sure safe autonomous driving can be realised based on vehicular sensors only without any communication to other road participants or road infrastructure. However, such an intrinsically safe approach limits driving comfort and reduces road capacity. The local information exchange between cooperative road users and with road infrastructure based on short-range communication enables enhancements of fore-sighted driving. By this road safety, traffic efficiency and driving comfort can be improved significantly. Tele-driving might be required as fallback solution for automated driving vehicles to overcome unusual situations which cannot be handled by the automated vehicle itself. However, this fallback solution requires a reliable mobile wide-area communication like cellular (4G, 5G) providing sufficient bandwidth without any dead spot along the roads.
 Can cellular communication serve cooperative Day 1 use cases?As a basic principle mobile communication via cellular network requires a contract with a mobile network operator and is subject to costs. For serving the safety related Day 1 use cases by cellular network vehicles communicate to all other vehicles in their vicinity always by sending their information via the local base station to the backbone system of the cellular network which links the information back to each of the vehicles of interest. Edge computing at the base station can shorten this communication and reduces resulting delays. However, in case of a critical traffic situation the communication channel of the base station might become overloaded compromising the reliability of the (multi-point to multi-point) service. Other communication issues result from cases where the communicating vehicles belong to different mobile network operators especially when roaming is required. Also, possible dead spots along the roads might limit the quality of service of cellular communication for cooperative safety related use cases. Because of these reasons short-range connectionless broadcast V2X communication (point to multi-point) between the local cooperative road participants is more suitable for safety related use cases.
Cooperative V2X
 What makes cooperative V2X superior compared to other technologies?Cooperative V2X systems use the connectionless short-range communication ETSI ITS-G5 based on the automotive designed WLANp standard called IEEE 802.11p. ETSI ITS-G5 is a locally self-organising ad-hoc network, performing everywhere at any time where cooperative units come closer to each other. The ad-hoc communication fits quite well with the stochastic channel usage caused by varying frequency and data size of the messages. The data transmission is for free (no subscription required), offers required robustness and reliability, quality of service and fulfils functional safety requirements. It operates independent of third-party commercial driven decisions and of other commercial communication networks. The NGV successor standard called IEEE 802.11bd is designed to offer a seamless evolution of the radio technology which ensures efficient use of the allocated spectrum, continuous operation of implemented services and by this safeguarding previous taken investments.
 Does the cooperative V2X communication fit for passenger cars only?The short-range cooperative V2X communication can be used for all kinds of cooperative vehicles like passenger cars, trucks, public transport, working machines, agriculture machines as well as motorcycles, other powered-two/three-wheelers including pedelecs, e-bikes and other vulnerable road users. For the later one’s power supply and accurate positioning highlight the main technical challenges to be solved for enabling reliable safety related applications.
 Can the communication technologies LTE-V2X, C-V2X and ETSI ITS G5 understand and talk to each other?The mature ETSI ITS G5 communication technology has been especially designed for the stochastic message exchange with respect to frequency and size of the safety related messages. The robust ad-hoc short-range data exchange between vehicles and with road infrastructure performs anywhere at any time and offers seamless evolution with the NGV successor radio technology under development. This allows efficient usage of the allocated ITS spectrum and safeguards taken investments. Beginning 2020 first LTE-V2X PC5 radios entered the market. Unfortunately, LTE-V2X PC5 is not interoperable with the mature ETSI ITS G5 requiring its operation in a separate channel. The same holds to its successor 5G NR-V2X PC5 which is neither interoperable with ETSI ITS G5 nor with LTE-V2X PC5. The direct communication of LTE-V2X PC5 and 5G NR-V2X PC5 can coexist in the same channel but are not able to communicate to each other.
 Might multiple-mode-chipsets with multiple communication stacks be able to bridge the incompatibilities of the C-ITS short-range radio technologies?Already today some vendors offer dual-mode-chipsets allowing the customisation for DSRC / ETSI ITS G5 or LTE-V2X PC5 according to the regional market needs. A further mode would need to be added for 5G-NR-V2X PC5 in future. As APIs and upper layer communication stacks are the same costs for development, certification and maintenance can be reduced in case of global sourcing. However, parallel sending and receiving operation of the incompatible short-range radios are not possible due to interference. Already during the early standardisation phase the OEMs have repeatedly pointed out the need to reduce the costs in order to make the implementation of C-ITS economically sustainable. Thus, it seems unlikely that multiple short-range technologies will be implemented in the same vehicle for bridging the incompatibilities of the radio technologies.
 Can ETSI ITS G5 be used also for other domains than road traffic?The cooperative short-range communication radio based on the IEEE 802.11p WLANp standard has been especially designed to fulfil automotive requirements in real traffic scenarios and to ensure data communication at high speeds up to 500 km/h. These features enable the application of the radio technology also for other domains like railway. Several Rail2X projects have successfully proven smart services based on WLANp communication like train to infrastructure, train to railway crossings and train to railway station. 
 Does LTE-V2X PC5 outperform IEEE 802.11p WLANp?The IEEE 802.11p WLANp has proven its maturity. The technology is in operation on European roads in vehicles and RSUs being deployed since 2019. First LTE-V2X PC5 chipsets have entered the market by end of 2019. Due to the different levels of maturity studies comparing the performance of both radio technologies are mostly based on simulation. Some studies indicate that LTE-V2X PC5 outperforms IEEE 802.11p on link level while others show performance advantages of IEEE 802.11p under realistic conditions. The differences might be caused among others by functional differences of the programmed communication layer stack, the radio channel behaviour, triggering conditions and message sets, considered scenarios of road traffic and/or the key-performance indicators used. Sophisticated real-world simulation studies can be verified with measurements from road traffic and lab testing. Such sophisticated simulation studies based on detailed close to reality models show some performance advantages of the older IEEE 802.11p compared to newer LTE-V2X PC5 for relevant European traffic scenarios.
 How does the evolutionary path of LTE-V2X PC5 towards 5G NR-V2X PC5 look like?Specification of 5G NR-V2X PC5 will enable superior radio performance compared to LTE-V2X PC5. A requirement on backwards compatibility does not exist for 5G NR-V2X PC5 relative to LTE-V2X PC5 but both technologies shall be able to co-exist in the same radio channels. Thus, it is likely that 5G NR-V2X PC5 and LTE-V2X PC5 might be deployed in separate radio channels. With the current spectrum allocations this might cause a problem in some parts of the world if the IEEE 802.11p or LTE-V2X PC5 based equipment already has been deployed and is in operation.
 How is European C-ITS standardisation organised?The CAR 2 CAR Communication Consortium provides an industry-wide platform to harmonise the technical details from R&D projects and to forward harmonised white papers and to contribute to the European standardisation in ETSI. For this the CAR 2 CAR Communication Consortium has established a close liaison with ETSI to foster the exchange of C-ITS standardisation and technology.
 How is worldwide C-ITS standardisation enhanced?The CAR 2 CAR Communication Consortium supports initiatives of the European Commission like C-ITS Platform and its successor CCAM Platform. Close liaisons have been established among others with the Amsterdam Group, C-Roads Platform, European Commission, ETSI and other relevant Standardisation Organisations like CEN/ISO, IEEE and SAE to support the worldwide harmonisation.
The worldwide standardisation itself is performed by the Standardisation Organisations in particular ETSI TC ITS.
 In which frequency band is cooperative V2X operated? Around the world the ITS frequency band has been allocated in the 5.9 GHz spectrum. In Europe the ECC decisions (08)01[ER-65] and EC decision 2008/671/EC build the legal basis for the operation of an ITS G5 system in the spectrum band 5855MHz to 5905MHz split into 5 channels with 10MHz. Due to overlapping with the SRD band the lower 2 channels from 5855MHz to 5875MHz are for traffic efficiency application whereas the 3 channels from 5875MHz to 5905MHz are allocated to traffic safety applications. 
As urban rail shall be integrated in the European C-ITS system further 2 channels from 5905MHz to 5925MHz are made available for the 5.9 GHz ITS spectrum.
 Which channel of the ITS Spectrum is used for deployment of Day 1 services in Europe? Deployment of cooperative automotive and infrastructure Day 1 services as listed by the Amsterdam Group and EU ITS-Platform use only one channel of the allocated 5.9 GHz ITS spectrum. The safety channel 5875MHz to 5885MHz is used for the operation of the Day 1 services.
 Does the ETSI ITS G5 operation interfere with other ITS services?The CAR 2 CAR Communication Consortium and ETSI ITS G5 are committed to the provision of interference mitigation with other existing communication systems used in neighboured channels. The tolling system operated in the band 5795MHz to 5815MHz has to be protected by a significantly reduced spurious emission level of a cooperative V2X system in that band or equivalent mechanisms like the reduction of the duty cycle. Urban Rail systems are operated in the band 5915MHz to 5925MHz. ETSI is working on sharing mechanisms between ETSI ITS G5 and Urban Rail systems. Urban Rail systems have priority over any kind of road ITS systems in this band.
 Which consequences result from parallel implementation of ETSI ITS G5 and LTE-V2X PC5 radios in vehicles, RSUs and other devices?The short-range communication radios ETSI ITS-G5 and LTE-V2X PC5 are not interoperable and cannot communicate with each other. Implementation of both technologies requires their separate operation in different communication channels of the 5.9 GHz ITS spectrum without any harmful interference. For improving road safety and efficiency in this case vehicles and RSUs have to be equipped with both radio technologies resulting in higher costs and higher spectrum usage compared to the case of interoperable radios. As the available 5.9 GHz ITS spectrum is limited in all regions this results in a limitation to exploit the full potential of both cooperative short-range communication technologies. 
 How much spectrum is needed for supporting future Day 2 and Day 3+ cooperative services?Different organisations like the CAR 2 CAR Communication Consortium and ETSI TC ITS have analysed the ITS spectrum needs considering the known roadmaps related to cooperative ITS. The studies have clustered the known services e.g. to awareness, automation, infrastructure, prioritisation, environment / pollution and system like security, service announcement and position augmentation and highlight that some further stakeholders discuss usage of C-ITS in future but have not specified their needs so far. The detailed analysis of the known cooperative services come to the conclusion that a frequency range of more than 80 MHz is required for enabling the implementation of the considered future Day 2 and Day 3+ cooperative services. 
 When will the cooperative V2X functions come into series production?First OEMs already equip mass-market cars with cooperative V2X Day 1 functions as standard equipment as off 2019. The CAR 2 CAR Communication Consortium expects to have a noteworthy share of equipped cars on the roads in 2020+.
 How will the cooperative services of competitors distinguish from each other?Even the received data and the basic cooperative V2X system design are the same the integration in the car and the presentation in the display (HMI) will be individual and brand specific.
 Will there be retrofit solutions?No, for safety applications the integration into the car does not allow that in the moment.
 How can market penetration be enforced?The more applications and benefits the cooperative V2X system can offer the more vehicles will be equipped. The more brands, markets and infrastructure are involved, the faster the customers see the cooperative V2X benefits. Therefore, the integrated approach of considering the variety of V2V and V2I use cases is the appropriate course of action.
 What is the role of the CAR 2 CAR Communication Consortium?

The mission and the objectives of the CAR 2 CAR Communication Consortium are improving road safety and road efficiency and supporting automation based on cooperative V2X systems. Here the Consortium acts:

  • To enable and to guide the development of cooperative safety applications by specifying, prototyping and demonstrating the cooperative V2X system
  • To create and establish an open European industry profile for cooperative V2X systems based on ad-hoc ETSI ITS G5 components and to guarantee European-wide inter-vehicle interoperability and backwards compatibility 
  • To promote the allocation of a royalty free European wide exclusive 5.9 GHz ITS frequency band for cooperative V2X applications
  • To contribute to international standardisation of cooperative V2X systems especially in cooperation with ETSI TC ITS
  • To push the harmonisation of cooperative V2X standards worldwide
  • To cooperate with road infrastructure for aligning automotive V2I / I2V developments and deployments
  • To develop realistic deployment strategies and business framework to speed-up the market penetration
 Will the C-ITS implementation in the global market be based on one short-range communication technology or is a regional partitioning between different technologies likely?It is important to understand that short-range communication being either ETSI ITS-G5 or LTE-V2X PC5 do not require any infrastructure and function as an ad-hoc network. To obtain the traffic safety and efficiency benefits interoperability or same radio technology for cooperative vehicles and roadside units is required. As consequence of the fact that the two technologies cannot communicate with each other severe problems have to be solved to assist towards accident free traffic (vision zero) in case of parallel operation of both incompatible short-range radio technologies. 
During the standardisation the vehicle manufacturers have repeatedly stated the need for bringing down the cost of the C-ITS subsystem in order to make the implementation economical viable. Thus, it appears not likely that both short-range technologies would be implemented in the same vehicle. Also, as all messages in such a case would need to be repeated on both systems this would lead to multiple transmission of the same information causing a lack of spectrum for the V2X communication. Some of the vehicle manufacturers already have backend services in operation based on wide area cellular communication. In this case it can be recognised that they hesitate implementation of the short-range communication for the time being.
At present it does not appear likely that the world would see one single communication standing for V2X. The protocol stacks used in US, Japan and Europe have been developed differently for a long time considering different regional requirements. However, between US and Europe some level of cooperation and harmonisation has been performed aiming on the usage of the same hardware and availability of required data elements enabling same use cases in both regions. 
China is planning to implement LTE-V2X PC5 by 2024/25 as it is seen as a technology which is to a large degree developed by Chinese companies. Europe favours to continue the deployment of ETSI ITS-G5. In addition, the standardisation of the 5G based short-range communication NR-V2X PC5 will be completed soon and will neither be backward compatible with ETSI ITS-G5 nor with LTE-V2X PC5. This fact might lead to further fragmentation of the global market. It is not likely that even a common hardware platform can be achieved.
 Will already implemented Day 1 services stay operational when new Day 2+ services will be rolled out?The cooperative V2X system based on ETSI ITS G5 is designed to offer interoperability across borders and brands. All future services have to fulfil the interoperability and backwards compatibility requirements. This ensures the further operation and service of older cooperative V2X systems in the field without any required update or upgrade. In line with these requirements, the NGV successor standard of the radio system allows flexible and seamless evolution, which ensures efficient use of the allocated spectrum, continuous operation of implemented services and by this safeguarding of investments taken.
 What comes next after the first Day 1 services being implemented on European roads?The phases of the roadmap build on top of each other. The initial Day 1 phase focuses on cooperative awareness and decentralised notification services involving cooperative vehicles and road infrastructure. With increasing market penetration Day 2 services are enabled improving and complementing the Day 1 services and offering collective perception services. Having these services in the field Day 3+ focuses on real cooperation by sharing intentions and coordination data. Cooperative Day 3 assisted and automated vehicles will share their trajectory and manoeuvre planning, support negotiation and coordination as well as active VRU advertisement.
Use Cases
 Which Day 1 use cases are offered by cooperative V2X?  The first cooperative vehicles offer cooperative awareness and decentralised notification services providing valuable user benefits already at low penetration rates. These Day 1 services comprise use cases like local hazard warning (e.g. broken-down vehicle, hard braking, end of traffic jam, slippery road), emergency vehicle warning, work zone warning, motorcycle indication up to cooperative ACC. Also, traffic light information and prioritisation of public transport and emergency vehicles are of high interest and are already being enabled by several front-runner cities.
 Can emergency vehicles benefit from cooperative V2X already today?Already the cooperative V2X Day 1 implementations allow cooperative emergency vehicles to use services like emergency vehicle warning, traffic light prioritisation or stationary vehicle warning. Next deployment phases will complement further sophisticated customised services.
 What is about public transport in cities? Which advantages does cooperative V2X offer for public transport?Generally public transport vehicles benefit from the cooperative V2X safety features as any other vehicles equipped with a cooperative V2X system. Furthermore, public transport vehicles are enabled to request prioritisation at intersections signalised with cooperative traffic lights. Also, the stationary vehicle warning might be used at bus stops to safeguard the passengers during (de-)boarding. Public transport is seen as one of the front-runner sectors benefitting from the developments in cooperative automated driving.
 What would be the benefit of integrating cooperative V2X into motorcycles?Increased road safety for motorcycle riders and other road users would be the key benefit. Looking into in-depth accident statistics, it appears that many accidents involving motorcycles are caused by overlooking the oncoming motorcycle. Roughly 30% of the researched accident configurations have the potential to be addressed by means of V2X technology. Consequently, several motorcycle manufacturers member to C2C-CC have actively contributed to ensuring that V2X is made compatible with motorcycles. This by means of establishing the Connected Motorcycle Consortium - CMC – that actively interacts with C2C-CC. This cooperation project CMC and its extension CMC-Next aims to mature the technology for motorcycles and also to support that future automated vehicles can reliably detect nearby powered two wheelers by means of onboard sensors and V2X connectivity.
 Can cooperative V2X support truck platooning?The deployed cooperative Day 1 services provide improved safety also for platoons. Today the brand independent truck platooning is still under development and ETSI ITS G5 is used for all tests on the European roads. New messages and control systems are under development enabling the automation of all platooning processes. Having tested and harmonised the new message sets in R&D projects their standardisation is required. Brand independent truck platooning is expected to be part of Day 2 deployment phase. 
 Does cooperative V2X also integrate agriculture vehicles and construction machines?Cooperative Day 1 V2X services can be used by agriculture vehicles too for further improving road safety.  Agriculture vehicles are special vehicles with unusual dimensions and behaviour for most of the drivers of other vehicles on the roads. Also, agriculture vehicles benefit from the safety features already provided today by Day 1 cooperative V2X systems. Avoiding accidents saves lives and directly pays-off during agricultural campaigns. Further cooperative V2X on-road and on-field applications are under development.
 Does cooperative V2X take care for Vulnerable Road Users (VRUs)? How will VRUs become part of the C-ITS?C-ITS aims on contributing to improve road safety and to avoid accidents (vision zero). Multiple R&D projects have investigated C-ITS use cases for improving safety and mobility of e.g. motorcycles, bicycles, pedestrians or blind and impaired people. The projects demonstrated that cooperative data exchange with smart devices of VRUs is feasible. However, power consumption and especially ensuring reliable accurate position of the VRU require some further technological developments for meeting the cooperative safety requirements. At intersections and other places with high risks for VRUs infrastructure based VRU detection systems have turned out as powerful devices to share sufficient accurate safety related information of VRUs. Also assisted and/or automated vehicles can detect VRUs and other non-cooperative road participants and share this Collective Perception information. These developments are seen as big step forward towards improving the road safety of VRUs by C-ITS and are considered for implementation during the Day 2 deployment phase.  
 Does cooperative V2X support the Green Deal for Europe policy?Cooperative V2X is designed to enable fore-sighted driving, to contribute to improving road safety and road efficiency and to support automation. Already Day 1 enables fore-sighted driving. Smooth travelling avoids unnecessary acceleration and deceleration, reduces the energy consumption, related emissions and particulates. Also looking to the traffic management, the collection of probe traffic data enables better organisation and management of the traffic, reducing shock waves and traffic jam as well as shifting priorities at cooperative signalised intersections. Next deployment phases will support further use cases providing enhanced Green Deal for Europe benefits.
 Are there some examples how automotive cooperative V2X use cases contribute to the Green Deal for Europe?Foresighted driving of cooperative vehicles enables reduced accelerations / decelerations and shorter headways. As a result, the foresighted driving strategies contribute to less energy / fuel consumption and reduction of emissions and noise.
Intersections have a strong impact on the traffic flow within cities. As among others cooperative traffic lights share their signal phase and timing information cooperative vehicles are enabled to adapt their strategies for approaching and passing the cooperative intersection. In case of stopping in front of the traffic lights also optimisation of the engine and power management are enabled. Such benefits of smooth travelling are also true for other road users like cooperative cargo-bicycles.
Cooperative V2X supports cooperative assisted and automated driving. In mixed traffic scenarios also non-cooperative vehicles following cooperative vehicles adopt their driving behaviour and increase the contributions to reduce energy / fuel consumption, emissions and noise. 
Furthermore, foresighted driving is expected to reduce the number of accidents. The reduction of the number of accidents and the severity of accidents adds further positive effects on saving lives, road capacity and traffic flow as well as on consumption of resources.
 Do cooperative V2X functionalities also serve Green Deal mobility scenarios with modal shifts to higher shares of bicycles and pedestrians?  The Corona Covid-2 pandemic led to an increased usage of bicycles in cities and pop-up bicycle lanes have become popular. Cities and road operators might shift priorities between road users and change the traffic organisation in their area of responsibility for meeting such changes of the demand. The cooperative ITS implementations provide high flexibility for supporting any modal split traffic scenario as the C-ITS message sets used for Day 1 services have been designed like a toolbox supporting all road users and a wide range of use cases. 
Cooperative V2X is designed to improve road safety and traffic efficiency. As a result, the cooperative V2X functionalities help to keep road accidents between vehicles and VRUs at a low level also in scenarios where bicycles and pedestrians have strongly increased their share in the traffic. 
In addition to the already outlined safety benefits projects like PedelACC in Hamburg show the potential of cooperative V2X also to support VRUs in improving their mobility e.g. when using cooperative pedelecs or cargo-bikes.
 Which Day 1 infrastructure-based services are offered to the road participants?The European C-Roads pilots have harmonised and tested the Day 1 infrastructure-based use cases for ensuring European-wide interoperability. As of 2020 the following services will be transferred into operation. Road Works Warning provides warnings at day building sites and moving construction sites. Hazardous Locations Notification informs about use cases like end of traffic jam or slippery road. In Vehicle Signage provides information about speed limits, no passing and other relevant traffic signs. For cities the signalised intersection is of high interest offering use cases like green light optimal speed advisory (GLOSA) or traffic light prioritisation e.g. for public transport and emergency vehicles.
 How will the cooperative V2X systems protect vulnerable road users (VRUs)?Infrastructure sensors as well as sensors of cooperative vehicles can be used for detecting VRUs and other non-equipped road users. By sharing their object information hidden objects can be recognised. Collective Perception is most suited to protect VRUs and road safety is expected to be improved significantly by this Day 2 service. Having solved the technical challenges of power and accurate positioning of VRUs in a successive step they shall become directly involved in the cooperative V2X system allowing active VRU advertisement. Today technical concepts for protecting VRU based on V2X equipped smartphones face many technical challenges like power consumption, accurate positioning, data protection and misbehaviour detection. Furthermore, the safety impact is limited since not all VRUs will actively use such a smartphone concept always (e.g. kids). Therefore, based on today’s available ETSI ITS-G5 technology the cooperation with intelligent road infrastructure enables most promising protection to all VRUs in sensitive areas.
 How will extended weather information help automated driving vehicle to drive more precise and saver?Even the most sophisticated automated or autonomous vehicle can only sense its immediate surrounding similar to a human driver. If the road condition changes rapidly there is a high likelihood that a vehicle travelling too fast might lose its traction momentarily. Traction control will of course allow some measure of mitigation of the hazard created by weather conditions, but it is only applicable within the limited sensorial range of the vehicle. However of course by communicating detected areas of hazards to other cooperative vehicles a swarm mentality can be envisaged to alert all road users as required. The solution promoted on extended weather information uses the network of cooperative ITS sensors and stations to create a consistent and accurate view of weather conditions across the entire road network that will form the basis of forewarning any vehicle that it is about to approach a hazardous location.
 How will Traffic Management support cooperative vehicles?Infrastructure Traffic Management Center systems (TMC) use cooperative vehicles to get a more precise overview of the current traffic situation by using cooperative V2X messages at all areas. For informing cooperative vehicles TMC systems use short- and long-range communication. Road Authorities have the sovereign responsibility for the Traffic Management and can use control processes and real time RSUs messages for sending information and warnings to the vehicles on their roads. By this the area wide traffic management (advanced traffic management) can influence the traffic flow on the roads and contributes to making road traffic safer and more efficient.
 Can the cooperative V2X system be used for other vehicle solution like trains, trams, or tubes? Rail2X is using the same cooperative V2X applications as cooperative vehicles. Use cases at infrastructure are used in a similar way for SPATEM / MAPEM / GLOSA / DENM / IVI. ETSI ITS-G5 is designed for automotive safety related applications and can be used for many other vehicle solutions. Several projects successfully have shown the maturity and high performance of the ETSI ITS G5 radio based on IEEE802.11p (WLANp).
Security & Privacy
 Why is asymmetric security with certificate required?Certificates with asymmetric keys are required in order to immediately trust V2X messages provided by another ETSI ITS-G5 C-ITS station, without the need for a backend or internet connection at reception time. With asymmetric security and certificates, all required security elements can be pre-loaded in a secure way to all senders and receivers to allow an immediate verification of the sender authentication including its permissions (authorisation) and to verify the integrity of received message contents. 
 Why is TLS security with X.509 certificates not applicable for short-range communication?There are two reasons why X.509 certificates are not well suited for short-range V2X communication. First, X.509 certificates are designed to identify the owner of the associated key with a unique subject element which is conflicting with the use of pseudonymous certificates in V2X communication to impede vehicle tracking. C-ITS certificates (ETSI TS 103 097 v1.3.1) contain explicit permissions to demonstrate the authorisation of a message sender which is not possible with basic X.509 certificates.
Secondly, the X.509 certificate structure is not size optimised and therefore approximately 3 to 4 times larger than C-ITS certificates. Since the certificate is attached to most V2X messages in the security header the size should be as small as possible to reduce bandwidth consumption and latency.
 Why do we need a certified security solution?The receiver of a V2X message should be able to trust the provided information to the same extend independent of the pseudonymous sender. The security solution impedes the enrolment of unauthorised devices, prevents extraction of sensitive key material from authorised devices, manipulation of message contents and defines the minimum security quality of authorised sender equipment to prevent malware sending fake messages. Certification ensures that relevant system components of different vendors fulfil the same defined minimum security requirements and quality.
 Can a vehicle be tracked using short-range communication?A vehicle can be equipped on a weekly basis with a fresh pool of 100 pseudonymous certificates for securing V2X messages that are switched after random usage periods. With each change of the certificate the vehicle is changing all other pseudonymous IDs applied in the message payload and different headers. A receiver inside communication range of another vehicle can temporarily track its movements but is not able to recognise the vehicle when entering its communication range at another point in time because the vehicle is changing its pseudonymous IDs.
 Why do pseudonymous certificates have short validity?Pseudonymous certificates without any identifying element are applied to impede long-term vehicle tracking. The validity time and preloading period of certificates is limited to force the vehicle to contact the certificate provider (PKI) at latest every three months. In case of security issues, the vehicle can be blocked to get new certificates and therefore excluded from actively participating to V2X communication. A longer validity of pseudonymous certificates would also increase the risk of being able to track/identify a single vehicle.