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The Communication Architecture for an Interurban Traffic Management System Architecture.
2nd IFAC Symposium on Telematics Applications Politehnica University, Timisoara, Romania October 5-8, 2010
The Communication Architecture for an Interurban Traffic Management System Architecture. Corneliu Mihail Alexandrescu*. Radu Serban Timnea** * University “Politehnica” of Bucharest, Transports Faculty, Bucharest, Romania ( e-mail:[email protected]) ** University “Politehnica” of Bucharest, Transports Faculty, Bucharest, Romania ( e-mail:[email protected]) Abstract: The paper presents considerations regarding the architecture of an inter-urban traffic management system, emphasizing the aspects related to the communication architecture. The functional and physical architectures for the proposed system are briefly presented, by mentioning the traffic control measures included in the system and the system components. The communication architecture it is defined through the physical data flows exchanged between the subsystems and between the system and its terminator, and through the main requirements for each pair of emitter/receiver. Based on a thorough analysis, for each communication link there are mentioned the connection type, distance, frequency and other characteristics. and between the systems components, we must create the architecture of the interurban traffic management system.
1. INTRODUCTION The only viable solution for solving the problems raised by the constant increasing of traffic levels it is the implementation of dynamic traffic management systems, applied at transport corridor level.
2. INTERURBAN TRAFFIC MANAGEMENT SYSTEM ARCHITECTURE
A dynamic inter-urban traffic management system includes infrastructure elements that must be interconnected in order to assure the system objectives. These elements may be: physical components (video camera, variable message signs, and traffic signals), communication equipments, a traffic management centre, software and operators, politics and procedures and so on.
2.1 Interurban traffic management concepts The main objective of an interurban traffic management is to improve the travel conditions and safety for the interurban road network users. There are many alternative automatic traffic control measures that could be incorporated in such a system, but for the proposed system these control measures are: interurban traffic surveillance and control, automatic ramp metering, variable speed limits management, lane management, incident management, emergency management, traveller information through variable message signs, service zone management.
The idea of dynamism implies that the system receives traffic data in real time, process these data and makes decision regarding the most appropriate traffic control measures. These decisions are processed as commands; the commands are sent to the field equipments and their effects are measured again. The advantages of dynamic management became really important when the system must address “crisis”, such as unpredicted traffic events, incidents, or adverse weather, for example.
As mentioned before, the interurban traffic management system, as most of intelligent transport systems, must be built according to an architecture composed from three main components: the functional architecture, the physical architecture and the communication architecture.
Also, in order to offer maximum efficiency, it has to be an integrated system, in permanent link with other adjacent or similar systems, by adopting mutual traffic strategies and politics. The interurban traffic management system must be interconnected with several other systems and terminators, such as: adjacent urban traffic management systems, weather information systems, road maintenance systems, emergency intervention dispatcher, public transport systems, and pavement state monitoring systems. Other terminals that communicate with the proposed interurban traffic systems are: drivers, traffic, emergency vehicle drivers.
After a short presentation of the functional and physical architecture of the system, in order to offer a correct understanding of the subsystems and of the necessary connection between the subsystems and between the system and its external medium, the paper focuses on more detailed information regarding the communication architecture, the real backbone that support all the other components of the system.
In order to establish the necessary communication links for exchanging information between the system and its terminals
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TA 2010 Timisoara, Romania, Oct 5-8, 2010
interurban and urban traffic management, or public transport management), assures the interface with traffic management operators, commands the execution of traffic control commands, assures central incident management, informs travellers, and so on.
2.2 Functional Architecture From the functional point of view, the interurban traffic management system is composed from three functional areas, namely: traffic management functional area, incident management functional area and emergency management functional area. These functions were selected after establishing the main user needs that the system must satisfy, in order to accomplish its goals.
3. COMMUNICATION ARCHITECTURE FOR THE INTERURBAN TRAFFIC MANAGEMENT SYSTEM
Each functional area it is composed from high level and low level functions, and some of the high level functions are also divided in lower level functions.
3.1 Concepts
The traffic management functional area it is composed from the following high level functions: interurban traffic data collection, service zone occupancy control, interurban traffic strategies and predictions, interurban traffic data management, assuring facilities for interurban traffic management.
The communication architecture of the interurban traffic management system must cover the data exchange between the subsystems and between the system and its terminals. The communication architecture can be defined through the physical data flows that must be transferred and by establishing the communication requirements for each necessary data transmission.
The high functions selected as part of the incident management functional area are: incident detection, incident identification and classification, incident evaluation and necessary action assessment, interfacing with incident management operator.
For the proposed interurban traffic management system, there are implied two types of communications: internal (between the system components) and external (between the system and its terminals).
Finally, for the last functional area, the component functions are: receiving emergency call, emergency intervention management, emergency vehicle management, assuring control for the emergency operator, assuring access to emergency data.
3.2 Internal communications
All the high level functions and there components (if any) are exchanging data between themselves, with the system databases and with the system terminals through functional data flows. 2.3 Physical Architecture The functional architecture describes the integration of the functional architecture in order to form physical entities. These entities are equipments, modules and subsystems. At its highest level, the system is composed from three subsystems: the Local Infrastructure Subsystem(s) (LIS), the Local Processing Subsystem(s) (LPS) and the Central Interurban Traffic Management Subsystem (CITMS). The Local Infrastructure System assures all the functionality in the field and includes: sensors, controllers, traffic signals, variable message signs. The Local Processing Subsystem assures all the functionality needed for the local traffic control. It is an “intelligent” subsystem, having the capacity to process locally some commands. It also assures the connectivity between CITMS and LIS. The Central Interurban Traffic Management Subsystem assure all the central functions for interurban traffic management: collects the necessary data, process and archives data, exchange informations with other external systems (for
Fig. 1. Internal communications diagram
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The interurban traffic management system is a hierarchical system, with three levels: a central interurban traffic management subsystems (central location), one or more local processing subsystems (in the field), and one or more local infrastructure subsystems (in the field) (fig.1).
In conclusion, there must be established three types of communications: x x
The internal communications that are necessary are: central to field communications (CITMS - LPS) and field to field communications (LPS – LPS or LPS – LIS).
x
Central to field communications are bi-directional, as shown in Fig.1. The downlink communications include: commands to be applied by LIS: signalling plan, message to be displayed, variable speed limit (fig.2). Additional information regarding the data flows between the selected locations is provided in the physical architecture of the system and is not included in the topic of this paper.
Communication links with low frequency and not permanent (commands to field equipments) Permanent communication links, low data rate (traffic data, for example) Permanent or semi-permanent communication links, high data rate (like video streams).
In the following table there are mentioned the general characteristics for the communication link needed for each physical data flow between CITMS and LPS, and also the selected connectivity required.
Table 1. Central to field communications characteristics
In the table, P/Mp means point/multi-point communications. It can be observed that one CITMS can send information to 500 LPS, but receive data only from 100 LPS (the others are slave LPSs, that don’t have a direct communication link with the centre). A code message it is a memorised massage, containing equipment’s location and code and an instruction code from the equipment memory, which must be displayed. Text and graphical messages are special messages, not resident in equipment memory, but which represent prioritary commands from the operator. Finally, video data contain photo and video streams, transmitted in real time or at request.
Fig. 2. Central to field communications diagram The downlink communication it is established only when the existing commands must be modified. The quantities of data transmitted for each LPS are small for a session. It is possible that the same information should be transmitted to more than one LPS, so it is preferable to use a multipoint transmission. The emitter and receiver locations are fixed, so it is not absolutely necessary to use wireless communications. There are no special conditions regarding security and confidentiality, but the integrity of received data is essential.
Field to field communications are established between adjacent LPS or between LPS and LIS. As shown in Fig.1, every LIS communicates bi-directional with a correspondent LPS. Only some of the Local Processing Subsystem communicates with the CITMS so there are also necessary bidirectional communication between a master LPS and its adjacent slave LPSs. The latter type of data exchange will not be detailed, because the data gathered by the master LPS have the same characteristics and requirements as the data exchanged with its own LIS.
The uplink communication it is used to transmit collected data and reports to CITMS (fig.2). These informations must be transmitted periodically (at 1 minute intervals or less) so the communication link must assure a fast data transfer.
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The downlink (LPS-LIS) it is necessary only when new commands are received from the centre. The volume of data for each LIS is very small; the communication is point-tomultipoint (if the same data are transmitted to more than one LIS). Integrity and security conditions are the same as before.
In conclusion, there must be established two types of communications: x
x
LPS-LPS: For data transfer between the slave LPSs and the master LPS. Medium distance. Include all the data flows that are transmitted between the master LPS and CITMS and also special priority request from the emergency vehicle, received by the slave LPS. The first data flows were already described before, and their characteristics and requirements are included in Table 1. For the latter type of transmission, the characteristics will be included in Table 2. The transfer must be very fast, but the quantity of transmitted data is small. The master LPS must coordinates its actions with a medium of 4 other adjacent slave LPSs, as seen in Figure 3. LPS-LIS: bi-directional communications. Small distance (a detailed description below).
The uplink it is used especially for transmitting collected traffic data (high frequency and big volume). The equipment functionality state and the commands applied are also transmitted periodically (medium frequency, small volume). The Figure 5 depicts the uplink and downlink communications between LPS and LIS (the equipments included in LIS are not detailed, as in the following table).
Fig. 3. Adjacent LPS communications links In fig. 4 there are depicted the links for LPS-LPS communication.
Fig. 5. LPS to LIS communications diagram In Table 2 we present the general characteristics for the communication link of each physical data flow (except the ones presented in Table 1) that must be transmitted between adjacent LPS or between LPS and LIS, and also the selected communication medium. It is assumed that one LIS can contain at most 1 traffic signal, 10 sensors, 3 variable message signs, 3 variable limit signs, 3 lane restriction signs and 3 service zone information signs.
Fig. 4. LPS to LPS communications diagram The LPS-LIS communication link assures the transport of the following physical data flows: x
x
From LPS to LIS (downlink): one of the commands received from CITMS (according to the respective SIL) or the signalling plan processed by LPS, in order to assure local priority.
3.3 External communications
From LIS to LPS (uplink): traffic data, equipments functionality data and the applied command (in order that LPS can create reports about equipment fault and command execution).
The external communications refer to the system link with its terminals. Each of the mentioned subsystems exchanges data with some or all of the terminals. Also, it must be specified that some of the exchanged physical data flows don’t require specific communication links (such as the man-machine interface).
For both types of connections, the characteristics regarding transmission frequency and message volume are the same as before. The distances are very short. 98
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Table 2. Field to field communications characteristics
Fig. 6. External communications diagram
As seen in Figure 6, the central subsystem (CITMS) communicates with all terminals. The Local Infrastructure Subsystem receives data from Traffic, receives emergency priority request from the Emergency Vehicle terminal and communicates information (through traffic signals or variable message signs) to drivers. Occasionally, LPS can communicate directly to Urban Traffic Management System, in order to coordinates its activity to grant local priority to emergency vehicles.
Table 3. External communications characteristics
The diagram of interurban traffic management system external communications it is presented in fig.6. The characteristics and requirements for external communications are presented in Table 3. As specified in the table, some of the physical data flows don’t require special communications links (for example, man-machine interface, physical interfaces).
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4. CONCLUSIONS The paper presents considerations regarding the architecture of an inter-urban traffic management system, emphasizing the aspects related to the communication architecture. In order to offer a better understanding of the system, its components, its terminals and functionality, we offer diagrams that present all the inter-connections involved. The tables present the general characteristics and requirements for the communication links. Even if the paper describes a general architecture, this can be easily applied to specific configuration system, maintaining the main characteristics and requirements. The advantage of building a new system according to a logical architecture is the possibility to interconnect the mentioned system with other existing systems and also the correspondence with the standard equipments and communication links.
REFERENCES Alexandrescu C.M., Timnea R.S (2009) Inter-urban Traffic Management - Concepts. Physical Architecture. Proceedings of IV-th National Conference / The Academic Days of Academy of Technical Science in Romania, vol no.1, pg. 83-88, Editura AGIR, ISSN 20666586, Iasi, Romania. Timnea R.S (2009). Contributions regarding the automatic control methods for interurban road traffic. PhD Thesis. Unpublished. Timnea R.S, Minea M., Nemtanu F.C. (2004). The ITS Architecture – One of the Most Important Component for Planning and Developing of the Intelligent Transportation Systems and a New Approach of the Information and Communication Systems in Transports Field. In: International Congress CONAT 2004, pp.178, ISBN 973635-394-X. Brasov, Romania.
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The Communication Architecture for an Interurban Traffic Management System Architecture. Corneliu Mihail Alexandrescu*. Radu Serban Timnea** * University “Politehnica” of Bucharest, Transports Faculty, Bucharest, Romania ( e-mail:[email protected]) ** University “Politehnica” of Bucharest, Transports Faculty, Bucharest, Romania ( e-mail:[email protected]) Abstract: The paper presents considerations regarding the architecture of an inter-urban traffic management system, emphasizing the aspects related to the communication architecture. The functional and physical architectures for the proposed system are briefly presented, by mentioning the traffic control measures included in the system and the system components. The communication architecture it is defined through the physical data flows exchanged between the subsystems and between the system and its terminator, and through the main requirements for each pair of emitter/receiver. Based on a thorough analysis, for each communication link there are mentioned the connection type, distance, frequency and other characteristics. and between the systems components, we must create the architecture of the interurban traffic management system.
1. INTRODUCTION The only viable solution for solving the problems raised by the constant increasing of traffic levels it is the implementation of dynamic traffic management systems, applied at transport corridor level.
2. INTERURBAN TRAFFIC MANAGEMENT SYSTEM ARCHITECTURE
A dynamic inter-urban traffic management system includes infrastructure elements that must be interconnected in order to assure the system objectives. These elements may be: physical components (video camera, variable message signs, and traffic signals), communication equipments, a traffic management centre, software and operators, politics and procedures and so on.
2.1 Interurban traffic management concepts The main objective of an interurban traffic management is to improve the travel conditions and safety for the interurban road network users. There are many alternative automatic traffic control measures that could be incorporated in such a system, but for the proposed system these control measures are: interurban traffic surveillance and control, automatic ramp metering, variable speed limits management, lane management, incident management, emergency management, traveller information through variable message signs, service zone management.
The idea of dynamism implies that the system receives traffic data in real time, process these data and makes decision regarding the most appropriate traffic control measures. These decisions are processed as commands; the commands are sent to the field equipments and their effects are measured again. The advantages of dynamic management became really important when the system must address “crisis”, such as unpredicted traffic events, incidents, or adverse weather, for example.
As mentioned before, the interurban traffic management system, as most of intelligent transport systems, must be built according to an architecture composed from three main components: the functional architecture, the physical architecture and the communication architecture.
Also, in order to offer maximum efficiency, it has to be an integrated system, in permanent link with other adjacent or similar systems, by adopting mutual traffic strategies and politics. The interurban traffic management system must be interconnected with several other systems and terminators, such as: adjacent urban traffic management systems, weather information systems, road maintenance systems, emergency intervention dispatcher, public transport systems, and pavement state monitoring systems. Other terminals that communicate with the proposed interurban traffic systems are: drivers, traffic, emergency vehicle drivers.
After a short presentation of the functional and physical architecture of the system, in order to offer a correct understanding of the subsystems and of the necessary connection between the subsystems and between the system and its external medium, the paper focuses on more detailed information regarding the communication architecture, the real backbone that support all the other components of the system.
In order to establish the necessary communication links for exchanging information between the system and its terminals
978-3-902661-84-5/10/$20.00 © 2010 IFAC
95
10.3182/20101005-4-RO-2018.00032
TA 2010 Timisoara, Romania, Oct 5-8, 2010
interurban and urban traffic management, or public transport management), assures the interface with traffic management operators, commands the execution of traffic control commands, assures central incident management, informs travellers, and so on.
2.2 Functional Architecture From the functional point of view, the interurban traffic management system is composed from three functional areas, namely: traffic management functional area, incident management functional area and emergency management functional area. These functions were selected after establishing the main user needs that the system must satisfy, in order to accomplish its goals.
3. COMMUNICATION ARCHITECTURE FOR THE INTERURBAN TRAFFIC MANAGEMENT SYSTEM
Each functional area it is composed from high level and low level functions, and some of the high level functions are also divided in lower level functions.
3.1 Concepts
The traffic management functional area it is composed from the following high level functions: interurban traffic data collection, service zone occupancy control, interurban traffic strategies and predictions, interurban traffic data management, assuring facilities for interurban traffic management.
The communication architecture of the interurban traffic management system must cover the data exchange between the subsystems and between the system and its terminals. The communication architecture can be defined through the physical data flows that must be transferred and by establishing the communication requirements for each necessary data transmission.
The high functions selected as part of the incident management functional area are: incident detection, incident identification and classification, incident evaluation and necessary action assessment, interfacing with incident management operator.
For the proposed interurban traffic management system, there are implied two types of communications: internal (between the system components) and external (between the system and its terminals).
Finally, for the last functional area, the component functions are: receiving emergency call, emergency intervention management, emergency vehicle management, assuring control for the emergency operator, assuring access to emergency data.
3.2 Internal communications
All the high level functions and there components (if any) are exchanging data between themselves, with the system databases and with the system terminals through functional data flows. 2.3 Physical Architecture The functional architecture describes the integration of the functional architecture in order to form physical entities. These entities are equipments, modules and subsystems. At its highest level, the system is composed from three subsystems: the Local Infrastructure Subsystem(s) (LIS), the Local Processing Subsystem(s) (LPS) and the Central Interurban Traffic Management Subsystem (CITMS). The Local Infrastructure System assures all the functionality in the field and includes: sensors, controllers, traffic signals, variable message signs. The Local Processing Subsystem assures all the functionality needed for the local traffic control. It is an “intelligent” subsystem, having the capacity to process locally some commands. It also assures the connectivity between CITMS and LIS. The Central Interurban Traffic Management Subsystem assure all the central functions for interurban traffic management: collects the necessary data, process and archives data, exchange informations with other external systems (for
Fig. 1. Internal communications diagram
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The interurban traffic management system is a hierarchical system, with three levels: a central interurban traffic management subsystems (central location), one or more local processing subsystems (in the field), and one or more local infrastructure subsystems (in the field) (fig.1).
In conclusion, there must be established three types of communications: x x
The internal communications that are necessary are: central to field communications (CITMS - LPS) and field to field communications (LPS – LPS or LPS – LIS).
x
Central to field communications are bi-directional, as shown in Fig.1. The downlink communications include: commands to be applied by LIS: signalling plan, message to be displayed, variable speed limit (fig.2). Additional information regarding the data flows between the selected locations is provided in the physical architecture of the system and is not included in the topic of this paper.
Communication links with low frequency and not permanent (commands to field equipments) Permanent communication links, low data rate (traffic data, for example) Permanent or semi-permanent communication links, high data rate (like video streams).
In the following table there are mentioned the general characteristics for the communication link needed for each physical data flow between CITMS and LPS, and also the selected connectivity required.
Table 1. Central to field communications characteristics
In the table, P/Mp means point/multi-point communications. It can be observed that one CITMS can send information to 500 LPS, but receive data only from 100 LPS (the others are slave LPSs, that don’t have a direct communication link with the centre). A code message it is a memorised massage, containing equipment’s location and code and an instruction code from the equipment memory, which must be displayed. Text and graphical messages are special messages, not resident in equipment memory, but which represent prioritary commands from the operator. Finally, video data contain photo and video streams, transmitted in real time or at request.
Fig. 2. Central to field communications diagram The downlink communication it is established only when the existing commands must be modified. The quantities of data transmitted for each LPS are small for a session. It is possible that the same information should be transmitted to more than one LPS, so it is preferable to use a multipoint transmission. The emitter and receiver locations are fixed, so it is not absolutely necessary to use wireless communications. There are no special conditions regarding security and confidentiality, but the integrity of received data is essential.
Field to field communications are established between adjacent LPS or between LPS and LIS. As shown in Fig.1, every LIS communicates bi-directional with a correspondent LPS. Only some of the Local Processing Subsystem communicates with the CITMS so there are also necessary bidirectional communication between a master LPS and its adjacent slave LPSs. The latter type of data exchange will not be detailed, because the data gathered by the master LPS have the same characteristics and requirements as the data exchanged with its own LIS.
The uplink communication it is used to transmit collected data and reports to CITMS (fig.2). These informations must be transmitted periodically (at 1 minute intervals or less) so the communication link must assure a fast data transfer.
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The downlink (LPS-LIS) it is necessary only when new commands are received from the centre. The volume of data for each LIS is very small; the communication is point-tomultipoint (if the same data are transmitted to more than one LIS). Integrity and security conditions are the same as before.
In conclusion, there must be established two types of communications: x
x
LPS-LPS: For data transfer between the slave LPSs and the master LPS. Medium distance. Include all the data flows that are transmitted between the master LPS and CITMS and also special priority request from the emergency vehicle, received by the slave LPS. The first data flows were already described before, and their characteristics and requirements are included in Table 1. For the latter type of transmission, the characteristics will be included in Table 2. The transfer must be very fast, but the quantity of transmitted data is small. The master LPS must coordinates its actions with a medium of 4 other adjacent slave LPSs, as seen in Figure 3. LPS-LIS: bi-directional communications. Small distance (a detailed description below).
The uplink it is used especially for transmitting collected traffic data (high frequency and big volume). The equipment functionality state and the commands applied are also transmitted periodically (medium frequency, small volume). The Figure 5 depicts the uplink and downlink communications between LPS and LIS (the equipments included in LIS are not detailed, as in the following table).
Fig. 3. Adjacent LPS communications links In fig. 4 there are depicted the links for LPS-LPS communication.
Fig. 5. LPS to LIS communications diagram In Table 2 we present the general characteristics for the communication link of each physical data flow (except the ones presented in Table 1) that must be transmitted between adjacent LPS or between LPS and LIS, and also the selected communication medium. It is assumed that one LIS can contain at most 1 traffic signal, 10 sensors, 3 variable message signs, 3 variable limit signs, 3 lane restriction signs and 3 service zone information signs.
Fig. 4. LPS to LPS communications diagram The LPS-LIS communication link assures the transport of the following physical data flows: x
x
From LPS to LIS (downlink): one of the commands received from CITMS (according to the respective SIL) or the signalling plan processed by LPS, in order to assure local priority.
3.3 External communications
From LIS to LPS (uplink): traffic data, equipments functionality data and the applied command (in order that LPS can create reports about equipment fault and command execution).
The external communications refer to the system link with its terminals. Each of the mentioned subsystems exchanges data with some or all of the terminals. Also, it must be specified that some of the exchanged physical data flows don’t require specific communication links (such as the man-machine interface).
For both types of connections, the characteristics regarding transmission frequency and message volume are the same as before. The distances are very short. 98
TA 2010 Timisoara, Romania, Oct 5-8, 2010
Table 2. Field to field communications characteristics
Fig. 6. External communications diagram
As seen in Figure 6, the central subsystem (CITMS) communicates with all terminals. The Local Infrastructure Subsystem receives data from Traffic, receives emergency priority request from the Emergency Vehicle terminal and communicates information (through traffic signals or variable message signs) to drivers. Occasionally, LPS can communicate directly to Urban Traffic Management System, in order to coordinates its activity to grant local priority to emergency vehicles.
Table 3. External communications characteristics
The diagram of interurban traffic management system external communications it is presented in fig.6. The characteristics and requirements for external communications are presented in Table 3. As specified in the table, some of the physical data flows don’t require special communications links (for example, man-machine interface, physical interfaces).
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4. CONCLUSIONS The paper presents considerations regarding the architecture of an inter-urban traffic management system, emphasizing the aspects related to the communication architecture. In order to offer a better understanding of the system, its components, its terminals and functionality, we offer diagrams that present all the inter-connections involved. The tables present the general characteristics and requirements for the communication links. Even if the paper describes a general architecture, this can be easily applied to specific configuration system, maintaining the main characteristics and requirements. The advantage of building a new system according to a logical architecture is the possibility to interconnect the mentioned system with other existing systems and also the correspondence with the standard equipments and communication links.
REFERENCES Alexandrescu C.M., Timnea R.S (2009) Inter-urban Traffic Management - Concepts. Physical Architecture. Proceedings of IV-th National Conference / The Academic Days of Academy of Technical Science in Romania, vol no.1, pg. 83-88, Editura AGIR, ISSN 20666586, Iasi, Romania. Timnea R.S (2009). Contributions regarding the automatic control methods for interurban road traffic. PhD Thesis. Unpublished. Timnea R.S, Minea M., Nemtanu F.C. (2004). The ITS Architecture – One of the Most Important Component for Planning and Developing of the Intelligent Transportation Systems and a New Approach of the Information and Communication Systems in Transports Field. In: International Congress CONAT 2004, pp.178, ISBN 973635-394-X. Brasov, Romania.
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