Intelligent Transport Systems

The present invention relates to the provision of cooperative awareness (CA) messages in intelligent transport systems (ITS).

Intelligent Transport Systems (ITS), as defined by the European Telecommunications Standards Institute (ETSI), include various types of communication between vehicles (e.g. car-to-car) and between vehicles and fixed locations (e.g. car-to-infrastructure). ITS are not restricted to road transport as such, as they also include the use of information and communication technologies (ICT) for rail, water and air transport, including navigation systems. In general, the various types of ITS rely on radio services for communication and use dedicated technologies.

During their work on ITS, ETSI came up with multiple use cases, requirements, an architecture model, and two types of basic services cooperative awareness basic service (CABS) and decentralized environmental notification (DEN) basic service (DENBS). Cooperative awareness within road traffic environment means that road users and roadside units (infrastructure elements) are informed about each other's position, dynamics and attributes. Road users are all kind of vehicles like cars, trucks, motorcycles, bicycles or even pedestrians and roadside infrastructure equipment includes road signs, traffic lights or barriers and gates. The awareness of each other is the basis for several road safety and traffic efficiency applications with many use cases as described in ETSI TR 102 638.

Cooperative awareness is achieved by regular exchange of information among vehicles (vehicie-to-vehicle (V2V), in general all kind of road users) and between vehicles and roadside infrastructure equipment (vehicle-to-infrastructure (V2I) and infrastructure-to- vehicle (I2V)) based on wireless networks, called V2X networks. It is very likely that the next generation of 3GPP's cellular communication network (for example, "3GPP LTE- Advanced Pro" or "3GPP's upcoming 5G technology") will be among the networks supporting the exchange of ETSI's CA and DEN messages. In 3GPP several work items exist to address V2V and V2I requirements.

The information to be exchanged for CA may be packed up in a CA message (CAM) that may be transmitted either periodically or if needed. The construction, management and processing of CAMs is done by the CABS, which is part of the facilities layer within the ITS communication architecture ETSI EN 302 665 supporting several ITS applications. The CABS is a mandatory facility for all kind of ITS-Stations (ITS-S), which take part in the road traffic (i.e. vehicle ITS-S, personal ITS-S, and so on). As mentioned above ETSI has collected a lot of use cases for derivation of service requirements. Based on this, many messages (both CAM and DENM) were defined.

However, the existing messages are defined to inform about physical information regarding vehicles and their environment, e.g. about known or measured physical dimensions (vehicle speed, vehicle type, direction, crash status, ...) or given properties like traffic priorities (police, ambulance, ... ). The current standard is completely lacking additional

communication means for "cooperative road usage", i.e. for fair and safe driving in situations in which the physical description of the environment does not lead to satisfying driving conditions. As an example, we think of the usual "give way" procedure used by humans to waive their right to drive in favour of a safer, more efficient and fairer traffic flow.

Thus, a dedicated solution for "yielding" or "giving way" is missing in situations where no traffic signs are installed, any installed signalling is unclear, temporarily unavailable, malfunctioning, out-of-order, or in other out of the ordinary situations (e.g. driving learner, U-turns, etc.), or autonomously driven vehicles are on the road.

If cars are facing a situation in which manual settlement is required among two or more road users, human drivers could either use hand gestures or flash their headlights a few times in order to coordinate the right of way. Both of these manual signalling options share the drawback that the legal situation is difficult to evaluate later on (i.e. the accountability is difficult to judge, if an accident had happened in such situations). In case of autonomous driving, manual signalling is not feasible.

Known arrangements for regulating traffic includes those described in the following documents: WO 2015/198226 A1 , DE 10 2014 008 413 A1 , US 2015/0194053 A1 , US 2015/0170513 A1 and US 8,587,418 B2. While these documents describe various signalling means and control algorithms, none of them describe cooperative awareness messaging schemes. US 2015/0228195 A1 describes a method for providing vehicle synchronization to facilitate a crossing. A pedestrian wishing to cross a road signals their intention which is detected by a module in one vehicle which then communicates with other vehicles in the vicinity in order to synchronise the traffic to stop and allow the pedestrian to cross. US 2013/0282357 A1 describes a V2V communication protocol including various messages and codes for facilitating traffic management. In a further document, US 2016/0035221 A1 , a system and method for traffic guidance is described in which infrastructure equipment exchanges messages with vehicle based units together with V2V communication.

The present invention provides a method for enhancing a cooperative awareness arrangement in which information is exchanged between vehicles using mobile

communication transmissions, the method comprising transmitting by a first vehicle a request for a resolution of a traffic situation concerning the first vehicle and a second vehicle; and receiving by the first vehicle a response to the request for the resolution of the traffic situation, the response determining actions by the first and second vehicles, the request transmitted by the first vehicle including vehicle characterization information for determining a right of way between the first vehicle and the second vehicle, the vehicle characterization information including at least one of a vehicle occupancy level, a vehicle classification, a vehicle weight and an energy consumption estimate.

The method of the invention provides inter-vehicle cooperative awareness information relating to a traffic situation which may affect progress of the vehicle. In particular, the invention in one aspect introduces at least one new message for inclusion in ETSI's CABS that can be used for signalling "I am giving way to you" (or, to put it another way: Ί am waiving my right of way") in situations where traffic signs are unavailable, or any installed signalling is malfunctioning (e.g., at intersections where traffic light are temporarily out-of-order); or traffic rules do not result into a unique priority for all involved road users; or traffic rules lead to un-economic (a heavy truck has to apply the brakes for a lightweight car) or un-comfortable (lot of cars have to wait for a single car) situation, or to a safety issue (a car has to apply the brakes strongly to give way to another car); or vehicles are driven autonomously (i.e. in an automated driving scenario with no or limited interaction with a human-being acting as a driver).

In addition, the invention provides a method to trigger dissemination of the (at least one) message (e.g. via an additional button deployed in the car's dash board or in a shift lever associated with a car's steering wheel, and so on). The dissemination/reception of the message(s), including a time stamp and/or a location stamp may be recorded for liability purposes, so that there is proof in case an accident occurs. The storage of the information may take place in the involved vehicles and/or in one of the roadside units nearby (or generally, in roadside infrastructure equipment). Another aspect of the present invention is the processing of the at least one new message to be used for signalling Ί am giving way to you" in a roadside infrastructure equipment (or, generally, by a V2X network element, such as a CA server) and various acknowledgement options. One acknowledgement option could be a single "your request was (not) successfully received", another option could be a more sophisticated new CAM containing an order of intersection entering/crossing permissions.

Furthermore, the Ί am giving way" function may be coupled with a car's lighting system (e.g., the headlight flash function), enabling the car to send light signals in a forward direction when the driver (or the computer operating the vehicle) initiates the dissemination of the message. Alternatively, or in addition to flashing headlights, the car could be enabled to send light signals in rearward direction (e.g., via the car's brake lights). Regardless of whether a new light source is introduced for this purpose, or whether existing lights (such as headlights or brake lights) are re-used, said light sources may be arranged to light or flash in a certain (i.e. predefined) lighting pattern (i.e. with a certain intensity, colour, or periodicity, etc.) thereby indicating the driver's (or computer's) decision to give way to someone else and preparing other road users for a potentially sudden reduction of speed. This aspect of the invention is especially useful to involve human drivers in (or inform them about) driving decisions done between the increasing number of autonomously driven cars.

In yet another embodiment the Ί am giving way" message triggers dissemination of at least one further CAM defined in ETSI TR 102 638, such as the "emergency electronic brake lights" message as described in section C.1. .1. or the "cooperative forward collision warning" message as described in section C.1.5.5. of ETSI TR 102 638 warning following road users about a particular driver's decision to yield in favour of another road user.

In yet another embodiment of this invention road users are prompted to make a decision (e.g., by a roadside infrastructure equipment) when they are approaching an uncontrolled intersection and may react with the dissemination of the "I am giving way" message if they wish to do so. In such a scenario the inventive prompt can be preceded by at least one further CAM defined in ETSI TR 102 638, such as the "intersection collision warning" message as described in section C.1.5.4. of ETSI TR 102 638. In a further embodiment of this invention the driver (or the computer) may revoke their decision to waive their right of way, if they wish to do so. In general, confusing situations at uncontrolled intersection/junctions can be cleared very easily. This is advantageous even under normal conditions. But it is even more beneficial, for example, under conditions such as when the visibility is poor (darkness, rain, fog, etc.), or when a vehicle that is steered autonomously (i.e. utilizing gestures is not possible) meets other vehicles.

By recording that and by whom the "I am giving way" message has been sent,

accountability can be proved later on if there is a need for investigations (e.g., by police, insurance companies, etc.). In some situations, it may be beneficial to record the sequential order of all disseminated "! am giving way" messages that were transmitted by the involved road users (i.e. road users that are located on the same spot, or involved in the same situation) for later accountability investigations.

A roadside infrastructure equipment (or, generally, a V2X network element, such as a CA server) is enabled to process and/or acknowledge the Ί am giving way" message(s) received from the road user(s). It may also determine a sequential order for the various road users for proceeding through the respective intersection thereby prioritizing the right of way among different vehicles. The "I am giving way" message may cause the vehicle's headlights to flash and/or activate the vehicle's brake lights. The interaction with the vehicle's illumination system is especially beneficial to avoid misuse of the functionality (by uninvoived road users) and to associate the CAM received over the air (either directly or with infrastructure involvement) with the proper vehicle.

The invention enables seamless integration of the message dissemination procedure into the existing CAM definitions, i.e. the "I am giving way" message can be preceded or followed by other already existing CAMs in a meaningful way.

Preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 shows an example of possible wireless links between vehicles and roadside

equipment;

Fig. 2 shows a typical traffic situation requiring resolution;

Fig. 3 shows an example message sequence chart for resolving the Fig. 2 situation; Fig. 4 shows an alternative message sequence chart for resolving the Fig. 2 situation; Fig. 5 shows a further traffic situation requiring resolution; Fig. 6 shows a message sequence chart for resolving the Fig. 5 situation;

Fig. 7 shows a still further traffic situation requiring resolution;

Fig. 8 shows a message sequence chart for resolving the Fig. 7 situation;

Fig. 9 shows another traffic situation requiring resolution; and

Fig. 10 shows a message sequence chart for resolving the Fig. 9 situation

In the context of this invention, a roadside infrastructure equipment 10 as shown in Fig. 1 may be mounted on street furniture, such as a lamp post or a bus stop, etc. It may be a simple relay node (i.e. forwarding data received over wireless Link A to wireless Link B and vice versa), or it may serve as an entry node into an infrastructure network (i.e. forwarding data received over at least one wireless Link A or B to at least one stationary server entity and vice versa). The radio access technology for the wireless connections A, B and C may be (based on) one of the following technologies: WLAN, UMTS, LTE, LTE-Advanced, LTE- Advanced-Pro, or -in general- any other radio communication technology, including D2D, V2 and V2X communication. For providing the various wireless links the roadside infrastructure equipment 10 may be operating in a licensed or in an unlicensed spectrum of radio frequencies.

The roadside infrastructure equipment 10 may be a base station or an access point operated by a mobile network operator (MNO) offering device-to-device (D2D) services or traffic safety services. Hence, a CA server may be located in one of the following elements: a roadside infrastructure equipment, the MNO's radio access network, the MNO's core network, or it may reside on an application server in the internet. An all-way-stop is an intersection system used predominantly in the United States of America, Canada and South Africa where traffic approaching it from all directions is required to stop before proceeding through the intersection. An a!l-way-stop may have multiple approaches and may be marked with a supplemental plate stating the number of approaches. Fig. 2 shows an example of a four-way-stop with four approaches to an intersection.

A motorist approaching an all-way-stop is always required to come to a complete stop before the stop line (or crosswalk). After a complete stop has been made, vehicles usually have the right of way to proceed through the intersection in an order that they arrived at the intersection. In the United States, if vehicles arrive at approximately the same time, each driver must yield to the drivers on their right, while in South Africa drivers must use common sense and make eye contact and gestures. Some countries have additional formal and informal rules which may or may not include special procedures for when all stop signs are approached simultaneously.

In this example, we assume that all four cars have approached the intersection at the same time and all four cars have come to a complete stop at approximately the same time. It is therefore hard to say which car has the right of way to proceed through the intersection first. This results into a confusing situation for the drivers. According to established practise, the drivers would now be required to use gestures to coordinate themselves and finally agree on the order how to proceed. Let's further assume visibility is poor (e.g., due to rain or darkness) and the drivers' hand signals (gestures) cannot be seen very clearly by the other road users. According to established practise, the drivers could now start flashing their headlights, which might be ambiguous as well, so this out of ordinary situation cannot be solved easily. A car which decides to "give way" (i.e. which volunteers to waive its right of way in favour of another road user) sends out a CAM of a type "giving way" over a wireless connection. This message may include the car's identity (plus a location stamp, a time stamp, a photo of the car's front view camera, an intersection ID, a vehicle category, and so on), and it may be transmitted either directly to the other cars waiting at this intersection (V2V type of communication), or indirectly with involvement of certain infrastructure elements (V2I type of communication). Said infrastructure element may be a roadside infrastructure equipment as described above. The decision to "give way" may be done in an autonomously driving car or a car supporting the driver with autonomous decisions using an algorithm

programmed to solve such traffic situation fairly. However, the decision may also be done by the driver himself who wants to "give way" simply by pressing a "give way" button that may be deployed in his/her steering wheel or installed in the car's dashboard.

In the example of Fig. 2 a CAM message of type "give way" is sent to a roadside

infrastructure equipment 10. Further instances of the CAM of type "give way" transmitted by other road users may be sent to the same or a different a roadside infrastructure

equipment. Said different instances of roadside infrastructure equipment may be

interconnected with one another. For instance, said instances of roadside infrastructure equipment may be base stations that are operated by the same or different MNO(s) in scope of 3GPP's upcoming traffic safety service. The various instances of the CAM may be stored in and assessed by a CA server entity that may be located in at least one of a roadside infrastructure equipment (e.g., a base station), a server element under control of the MNO (e.g., a core network element), or an application server under control of a third party offering traffic safety services (e.g., a CA server located on the internet). According to our invention, the order of the incoming CAMs of type "give way" may be recorded too if applicable (for accountability reasons).

A message sequence chart for the situation represented in Fig. 2 is shown in Fig. 3. Car #3 sends a "give way" CAM to the CA server. Each of cars #1 #2 and #4 may optionally send an indication of arrival message to the CA server, as indicated by the dashed arrows. The CA server records the information received. in a further embodiment, the CA server entity determines a sequential order for the various road users for proceeding through the respective intersection (one after another) and creates a new CAMs of type "right of way response". This message may be transmitted back to the vehicles/devices of ail involved road users as some kind of feedback message.

The group of recipients can be determined by the location stamp(s), intersection ID(s), etc. contained in the various novel CAMs of type "give way" (or of type "indication of arrival") that have been received previously. For instance, the CAM of type "right of way response" may contain the car's identities in the same order of the arrival of the CAMs of type "give way".

Fig. 4 shows a message sequence chart of such an embodiment. In the situation as shown in Fig. 2, each of cars #1 to #4 sends an indication of arrival CAM to the CA server which processes the received information. After processing, the CA server sends "right of way" responses to each of the four cars which may contain information pertaining to an order of proceeding through the intersection. In yet another embodiment, a "right of way" order may be calculated that differs from the order in which the CAMs of type "give way" have been received before (e.g., based on category of vehicle, weight of the vehicle, level of occupancy, and so on). Calculating a new order based on these pieces of information would for example enable de-prioritization of vehicles that are empty (in case of autonomous driving), and/or high-ranking of vehicles of heavy weight (as these type of vehicles usually require more energy to get back to full speed after having come to a full stop than light vehicles).

According to one embodiment of the present invention, the headlights of the relevant cars can be triggered to start flashing either by the transmission of a "give way" message, or (if the method comprises submission of feedback messages) by reception of a "right of way response" message. In the latter case, all cars of the group but one may activate their headlights (with the exemption of the car which is ranked highest in the order indicated by the CAM of type "right of way response"). Modulating the headlights is essentially a way to involve human drivers into the autonomous, machine driven process and inform them about the automatically derived decision.

In a further scenario shown in Fig. 5, car #3 has right of way as it is proceeding straight on. However, an obstacle (traffic jam, construction works, etc.) is detected right in front of it forcing it to slow down. Car #1 is indicating its intention to turn left, but it cannot be sure that car #3 would stop or slow down. Normally, some kind of manual coordination among the drivers is needed in order to solve this confusing situation for the drivers. Autonomous cars cannot deterministically solve the situation which will probably lead to a stalled situation.

In this example, we assume that car #3 decides to allow car #1 to turn left. According to normal practise, the driver of car #3 would now have to use gestures to indicate waiving of his/her right of way. Further for the sake of illustrating the invention, it is assumed visibility is poor (e.g., due to rain or darkness) and any drivers' hand signals (gestures) cannot be seen very clearly.

According to the invention the car which decides to "give way" (i.e. car #3 which wants to grant a right of way to car #1 ) sends out a CAM of type "give way". This message may include the car's identity (plus a location stamp, a time stamp, a photo of the car's front view camera, an intersection ID, and so on), and it may be transmitted either directly to the other cars nearby (V2V type of communication), or indirectly with involvement of certain infrastructure elements (V2I type of communication). Said infrastructure element may be a roadside infrastructure equipment as described above. In case car#3 is driven by a human driver the car may have means to initiate transmission of the CAM, e.g. the driver simply presses a "give way" button that may be deployed in his/her steering wheel or installed in the car's dashboard.

In the example of Fig. 5 the CAM message of type "give way" is sent to a roadside infrastructure equipment, for instance a base station operated by an MNO that is supporting 3GPP's upcoming traffic safety service. The CAM may be stored in and assessed by a CA server entity that may be located in at least one of a roadside infrastructure equipment (e.g., a base station), a server element under control of the MNO (e.g., a core network element), or an application server under control of a third party offering traffic safety services (e.g., a server located on the internet). According to one aspect of the invention, some information elements from the CAM message of type "give way" such as location stamp, a time stamp, a photo of the car's front view camera, an intersection ID, and so on may be stored for later accountability investigations. Fig. 6 shows a message sequence chart for the situation of Fig. 5. Car #3 transmits a "give way" message due to the presence of an obstruction in its path which is stored in the CA server. Optional messages may be transmitted, including an "intention to turn left" message sent by car #1 to the CA server which after processing results in an information message being sent by the CA server to car #3. A "give way acknowledgement" message may be sent by the CA server in response to the "give way" message sent by car #3 and further car #1 may be informed that car #3 is giving way.

Car #3 can be asked to react to an out of the ordinary traffic situation with a CAM of type "info". As indicated, this CAM may for instance be sent when another car has indicated its intention to turn left.

A CAM of type "give way ack(nowledgement)" may be transmitted back to car #3 as some kind of feedback message.

According to one embodiment of the present invention, the headlights of car #3 can be triggered to start flashing either upon transmission of the initial "give way" message, or (if the method comprises submission of feedback messages) upon reception of at least one of a "give way ack(nowledgement)" message by car #3 and a "give way message (forwarded)" by car #1.

A further embodiment of the invention may be implemented to deal with a situation such as a pedestrian wishing to cross the street. In this example, a car is equipped with an additional light source (with a lighting pattern and/or colour that is currently un-used in this context). The light is especially beneficial for autonomously driven cars that cannot make human eye contact or gestures. In case such light is deployed to support a human driver, it may be beneficial to place this light source near the driver's head, as both human beings are likely to seek eye contact in an out-of-ordinary situation like this. The additional light source could be mounted for instance at the rear view mirror shining in forward direction in green, so it would cast a very clear "walk" signal for pedestrians that intend to cross the street. The signal could also be an audio signal (similar to what pedestrian traffic lights emit for blind people). The audio signal may be generated in a loudspeaker deployed in the car and/or in the pedestrian's mobile device. The signal could also be a tactile signal generated by the pedestrian's mobile device, such as a vibration.

Such an arrangement is illustrated in Fig. 7. In this example, we assume that the car wants to allow the pedestrian to cross the street. Previously, the pedestrian cannot be sure that the car really stops in front of the cross-walk. So, before crossing the street the pedestrian is likely to seek a sign of the intended behaviour of the car. In case of an autonomously driven car, there is no such sign available yet. In case of a human driver, this would be eye contact with the driver. Furthermore, in the human driver case, the pedestrian likely expects the driver to use gestures to indicate that he has seen the pedestrian and also understood his intention. Let's assume visibility is poor (e.g., due to rain or darkness) and the driver's hand signals (gestures) cannot be seen very clearly by the pedestrian.

According to one aspect of the invention the car which wants to "give way" sends out the CAM of type "give way". This message may include the car's identity (plus a location stamp, a time stamp, a photo of the car's front view camera, a cross-walk ID, and so on), and it may be transmitted to the pedestrian's mobile device either directly (V2P (vehicle-to- pedestrian) type of communication), or indirectly with involvement of certain infrastructure elements (V2I type of communication). Said infrastructure element may be a roadside infrastructure equipment as described above. If the driver is a human being, means may exist that allow triggering the message transmission, e.g. a "give way" button that may be deployed in the driver's steering wheel or installed in the car's dash board.

In the example of Fig. 7 the CAM message of type "give way" is sent to a roadside infrastructure equipment, for instance a base station operated by an MNO that is supporting 3GPP's upcoming traffic safety service. The CAM may be stored in and assessed by a CA server entity that may be located in at least one of a roadside infrastructure equipment (e.g., a base station), a server element under control of the MNO (e.g., a core network element), or an application server under control of a third party offering traffic safety services (e.g., a server located on the Internet). According to the invention, some information elements from the CAM message of type "give way" such as location stamp, a time stamp, a photo of the car's front view camera, a cross-walk ID, and so on may be stored for later accountability investigations.

Fig. 8 shows a corresponding message chart, in response to a "give way" CAM, which is recorded by the CA server, an optional "give way message (forwarded)" is sent to the pedestrian. This optional "give way message (forwarded)" may trigger rendering of a visible, audible or tactile signal in the pedestrian's mobile device. Alternatively, the car may be instructed to provide a signal to the pedestrian such as a headlight flash, a dedicated optical signal or an audible signal.

The invention also provides for a prioritization of individual vehicles. In an example shown in Fig. 9, two autonomously driven cars are coming close to each other at a motorway ramp. Car #3 is a small car of little weight that is currently travelling empty, while car #1 is a large car of heavy weight with a passenger occupancy of five people. International traffic rules (and common sense as well) stipulate that moving traffic (such as car #3) has right of way over traffic entering a motorway (such as car #1 ).

Additionally, in the example scenario of Fig. 9 a "yield" sign is present for car #1 at the end of the ramp. Thus, according to state-of-the-art car #3 (the small one) has right of way and car #1 (the large one) has to yield to car #3. In the example traffic situation of Fig. 9 both autonomously driven cars detect that they are coming close to each other and that resolution of an out-of-ordinary "right of way" situation is potentially required. Detection of proximity may be achieved either directly via Link C or infrastructure assisted. Hence, both cars send out a CAM of type "right of way resolution request" to a roadside infrastructure equipment, for instance a base station operated by an MNO that is supporting 3GPP's upcoming D2D services or traffic safety service. The CAM may be stored in and assessed by a CA server entity that may be located in at least one of a roadside infrastructure equipment (e.g., a base station), a server element under control of the MNO (e.g., a core network element), or an application server under control of a third party offering traffic safety services (e.g., a server located on the internet). This message may include the car's identity (plus a location stamp, a time stamp, information about the passenger occupancy level, the weight of the vehicle, information about energy

consumption during an acceleration process, a ramp ID, and so on), and it may be transmitted to the other cars either directly (V2V type of communication), or indirectly with involvement of certain infrastructure elements (V2I type of communication, cf. Fig. 10). Said infrastructure element may be a roadside infrastructure equipment as described above.

According to the invention, some information elements from the CAM message of type "right of way resolution request" such as the vehicle ID, information about the passenger occupancy level, the weight of the vehicle, information about energy consumption during an acceleration process, ramp ID) may be used by the CA server entity to determine which car is given preference over the other.

The CA server entity then determines a meaningful order (at the respective location, e.g. the ramp in Fig. 9) for the two cars driving autonomously and creates a CAM of type "right of way resolution response". This message may be transmitted back to the vehicles/devices of all involved road users and may serve as a feedback message. The group of recipients can be determined by the vehicle ID(s), location stamp(s), ramp ID(s), etc. contained in the various CAMs of type "right of way resolution request" that have been received previously. There may be one CAM message of type "right of way resolution response" common for all recipients at a given location, or multiple dedicated messages. For instance, the CAM of type "right of way resolution response" may instruct car #3 (the small one) to give way for car #1 (the large one), in this example, it is economically justifiably to give preference to car #1 , as nobody is currently driving car #3 (or riding on it) and its weight (and energy consumption needed to get back to speed) is much smaller.

A corresponding message sequence chart is shown in Fig. 10. Detection of proximity triggers both cars to transmit "right of way resolution request" messages, which are then processed by a CA Server. The "right of way resolution request" messages may be triggered by a trigger message sent by the CA server but this is optional. Proximity may also be detected directly via Link C without any infrastructure involvement. After processing "right of way resolution response" messages are sent to both cars implementing an appropriate resolution of the situation. Car #3 may acknowledge reception of the "right of way resolution response" message, thereby acknowledging that it will yield.

With regard to the embodiments described, the following is to be noted.

The order of transmitting one of the CAMs defined in this invention and activating the light (and/or audio) signal was chosen arbitrarily in the examples above. In other words, this invention is supposed to cover also the following cases:

First an instance of the CAM is disseminated, then a corresponding light (and/or audio) signal is activated;

First the light (and/or audio) signal is activated, then a corresponding CAM is disseminated; Dissemination of the CAM and the corresponding light (and/or audio) signal coincide, or are at least initiated at the same time;

Either the CAM is disseminated, or the light signal is activated, or the audio signal is emitted. The figures show typical situations for right-hand traffic (continental Europe, U.S.A. etc.), i.e. for countries where regulations require all bidirectional traffic, unless otherwise directed, to keep to the right side of the road. It is obvious that the principles and solutions discussed in the present document can be easily adopted for left-hand traffic scenarios (Japan, United Kingdom etc.).