The basis for traffic management and incident management is the monitoring of real-time traffic conditions by probe vehicles and other sources. The systems aspect of ITS is increasingly complex, combining hardware, software, and communications to provide transportation services (See Managing ITS Implementation).
Communications networks are critical to the timely gathering of data and its distribution between operational systems, their functional components and road users. The communications layer of a system architecture is concerned with the accurate and timely exchange of information between different system components that support transport solutions. (See What is ITS Architecture) Common to many of the resources and activities of a Traffic Control Centre (TCC) are:
To ensure that a TCC has a comprehensive and continuous view of the road network, the communications services must be reliable. This means that they must be available most of the time and have the capacity to meet the requirements of applications. Ideally each interface should comply with publicly available communication standards that are supported by a competitive network of suppliers - to ensure that the communication architecture can be expanded.
Data communications are needed for the transmission of voice, video camera images and other data from CCTV cameras, traffic detectors, weather stations, emergency phones and tunnel monitoring systems. Communications also play a central part in distributing data for the management of the highway. The most common forms are:
The communication architecture identifies devices, roadside controllers, intermediate communication hubs and equipment needed at TCCs. A well-designed architecture allows expansion - such as the addition of more CCTV cameras (including high definition cameras), detectors located on other roads and voice and other data services.
Careful management of the communication network and its security is needed to maintain the performance of the communication links and to protect investments in communication systems. The communication network will also need to support the distribution of advisory and mandatory instructions to road users, such as Variable Message Signs (fixed and mobile) and Highway Advisory Radio (HAR) or other control signals. The communication network specification must to be designed with this in mind.
An effective traffic management operation relies on effective communication between agencies. This is not always fully achieved due to differences in organisational responsibilities and the lack of open, non-proprietary communications protocols that are in use – often because available standards-based interfaces have not been adopted.
The sensor equipment (such as loops, CCTV cameras) and the applications they serve, will determine the communication requirements and may be restricted by limited bandwidth. Typically, the data is collected and uploaded to a central location. For instance:
Communications using Internet Protocol (IP) television and Voice Over IP (VoIP) systems and components support road network management based on multi-media services, and are becoming more common. Standards are necessary to enable interoperability across interfaces. Ideally, equipment installed on the roadside should comply with standards for ‘field-to-centre’ communications – such as those standards authored by the NTCIP (21xx, 22xx and 23xx), Directorate-General for Mobility and Transport (European Commission) (DATEX), ISO (TC204), CEN (TC278) and the Transport Department of China (JT/T-series standards).
CCTV cameras are a common means of monitoring traffic and keeping track of incidents. Digital CCTV with image processing software can also be used to measure traffic flows, classify vehicles and to detect, verify and manage incidents. For example, in some parts of South Africa they are used to detect 80-85% of all incidents occurring on main roads. As a means of monitoring a road network the value of CCTV is unparalleled because it provides control centre operators with visual confirmation of an incident.
In general, CCTV cameras are distinguished by having either analogue or Internet Protocol (IP) communication interfaces. IP cameras may suffer from image compression (such as MPEG-4) but offer more flexibility when designing and scaling a CCTV system. If high-resolution IP cameras are used, the communication network capacity must match the data output demand of each camera – and this is potentially as high as 4Mb/sec. Otherwise the cameras need to be specified to balance image quality with frame rate. Some cameras have the capability to be configured to reduce their image quality and image reporting frequency.