The fundamental requirement of Intelligent Transport Systems is data and information about the transportation network (roads and highways). Data needs to be reliable, up-to-date, readily accessible and sufficiently comprehensive for planning and operational purposes. This is the “info-structure” upon which so many ITS applications depend. Base data is usually map-related and held in digital format such as a database of road links that connect known locations, or “nodes” on the network – each with a unique reference. (See Planning Procedures)
As an absolute minimum, network information will consist of a “gazetteer” (or index) that holds the codes and short descriptions of the road links, nodes and other locations, such as:
A network gazetteer can provide a basis for a navigation database if it is sufficiently detailed. (See Navigation and Positioning)
The type of inventory required for ITS equipment and assets deployed across the network will be determined to a great extent by local operational requirements and the ITS applications to be maintained and supported. Information about the ITS equipment and its location will require some form of data management system and an appropriate method of location referencing to support the spatial representation of information. Maintenance Management Systems (MMS) and Communications Management Systems (CMS) are relational databases that can be used to maintain an inventory of ITS equipment and the associated communications infrastructure. Sometimes a performance monitoring system and/or a fault detection system is included. This monitors critical aspects of the equipment or system performance and issues alerts to the maintenance contractor when faults are detected. this monitoring equipment may be referred as Outstation Monitoring Units (OMUs) or a Performance Monitoring System (PMS).
Building on the network description, and using whatever location referencing system is adopted, a variety of data will contribute to the intelligence base for Road Network Operations. They include for each road link:
The network intelligence base needs to be kept current and up-to-date, taking account of any significant modifications to the road network that are:
Where network operations are well-developed a comprehensive database will be maintained of future events likely to have an impact on network capacity. This will require consultation with key stakeholders such as local authorities and the emergency services. (See Planning and Reporting)
Further layers of network information will be generated by the traffic monitoring systems. Data from traffic monitoring has three primary functions in network operations:
These basic functions will be served by information available from a variety of sources – and a systematic approach to traffic monitoring will be needed. An organised, planned approach is essential, especially if the data is going to be used for:
Automatic traffic monitoring systems will supply data in real time on traffic volumes, vehicle speeds, point-to-point journey times and, in some cases, vehicle classification. This data needs to be time-stamped and stored with reference to the link(s) to which they relate, together with a record of the data source. (See Traffic and Network Status Monitoring)
Computer models of the road network are used to forecast future traffic conditions and predict journey times. Modelling makes use of data on link characteristics, junction capacities and whatever traffic and incident-related data is available – which may be dynamic in real-time or historical. Model estimates can be compared with results from traffic monitoring to aid calibration and validation. A network model can also be used to forecast the effects of a given traffic management strategy and identify the potential benefits of that strategy compared to a “do nothing” scenario or an alternative response plan. Modelling can also perform risk assessments or sensitivity testing around different response plans.
Network modelling is able to deliver more efficient strategic traffic management by validating the decisions taken, and by providing better information for network management planning purposes. It can also help provide enhanced travel information for road users, such as more accurate journey times and forecasts of traffic conditions. (See Traffic Models)
Different methods are used to provide location information depending on the technology that is available and the accuracy required. Many countries have an established national grid referencing system which needs to be interpreted to give global latitude and longitude coordinates. Examples of location referencing include global positioning and the Radio Data System Traffic Message Channel (RDS-TMC).
Global positioning (Latitude/Longitude)
Global Positioning Systems (GPS) provide a means for determining an object's location, in terms of latitude and longitude, based on signals received from multiple Global Nautomatic gation Satellite Systems (GNSS) – for example GPS satellites at the location of the GPS receiver. Besides location, GPS can be used to track vehicles and can provide effective fleet management and monitoring the progress of a vehicle along its route.
Radio Data System Traffic Message Channel (RDS-TMC)
Some countries – mostly in Europe – have invested heavily in location referencing for digital radio, known as the Traffic Message Channel (TMC). Using RDS-TMC technology only 16 data bits (the smallest unit of data in computing) are allocated to location coding. This means that the RDS-TMC location code tables are only able to refer to significant highway junctions (nodes) and lengths of road (links). (See http://en.wikipedia.org/wiki/Traffic_message_channel)
ITS systems typically use multiple servers for the different applications, workstations, and video displays in traffic control centres. The computer hardware plays a major role in any ITS system. It is responsible for:
In addition to computer hardware, some ITS applications (such as freeway and incident management systems) typically include graphical displays in the control centre to provide a visual description of the transport systems operations, captured from field cameras.
Graphics can be provided on the monitors of control room workstations, or on large graphics screen displays in the form of a video wall. These displays provide the main “window” (or view) into the traffic management system – and are usually based on a graphical representation or map of the highway network. They will show the on-road assets available for network monitoring and traffic control, such as signals and VMS, location of Emergency Roadside Telephones (ERTs) and CCTV cameras.