Between the vehicle systems
The most common method of enabling communication between vehicle systems is through the use of CAN (Controller Area Network) bus technology. Other technologies are also available for this purpose but tend to be more complex, heavier, unreliable and slower in terms of data transfer.
In transport vehicles the CANbus network generally forms part of the on-board computer through which each other vehicle system is integrated. Intelligent on-board computers are needed for ITS. These act as data servers which run individual systems as well as providing a communication platform between the systems via the CANbus network. The computers which are used are capable of running many connected systems at the same time, such as the engine control unit, antilock braking system, on-board automatic passenger counting system, the GPS system and the driver display system. The on-board computer system is a hardware platform which runs vehicle systems and allows installation of additional applications from other manufacturers. It facilitates communications between systems within a vehicle, the vehicle and the control centre, vehicles and other vehicles as well as vehicles and road side ITS equipment.
The CANbus network itself consists of a system of control units connected together in a linier network (bus) with all communications signals passing through each control unit (node). Each node can receive and transmit data in the form of a message and when a message is transmitted it is sent to each node. As each node has a unique identity they can be differentiated from each other and the message is only accepted by the node for which it was intended. Each node can request access to the bus at the same time but some nodes, such as the airbag control unit, have priority over others.
As the vehicles on-board computer facilitates communications between all of the vehicle systems it represents the centre of all vehicle related ITS applications. The technology allows for the integration of multiple systems and communication between the vehicle, control centre, roadside and other vehicles so that the capabilities of each system can be fully utilised.
Benefits and cautions
On-board computer systems integrating various on-board ITS systems provide improved ITS capabilities which allow a transport service operator to extract more information in a useful way. For example, driver behaviour monitoring devices such as accelerometers integrated with the navigation system through the on-board computer system allows for analysis of driver behaviour at specific sections of a route, and further integration of the radio system allows this data to be monitored in real-time at the control centre.
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