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.
Software and relational databases are required for ITS technologies to store, manage and archive network data. These are brought together as Archived Data Management Systems (ADMS) or what is sometimes called ITS Data Warehouses. ADMS offers an opportunity to take full advantage of the travel-related data collected by ITS devices in improving transport operations, planning and decision-making at minimal additional cost.
The technologies supporting ADMS are designed to archive, fuse, organise and analyse ITS data and can support a wide range of very useful applications such as:
The figure below shows an example of the system architecture designed for a simple ITS Data Warehouse being developed for the Buffalo-Niagara region in New York State USA. At the core of the system is a relational data base (such as Oracle or MySQL) which receives data from a wide range of sources including real-time traffic data (volumes, occupancies and speed), incident information, travel time and delay information, weather data, construction and work-zone information, and transit data (such as automatic vehicle location data). The relational database organises and fuses the data and information together – linking the different data streams through common identifiers – allowing a wide range of applications to be developed and deployed.
System architecture designed for a simple ITS Data Warehouse (Buffalo-Niagara Region New York State USA)
Among the data stored in ADMS are transport system inventory data, which can be used to facilitate the construction of detailed network models and traffic simulation models. Every link and associated junction in the network will need to be classified according to its strategic importance and capacity. Many ADMS are provided with functionalities that can convert the stored data into the required format for running different traffic simulation and analysis software.
A key benefit of having an ADMS is the ability to quantify network conditions in terms of travel times, speeds and traffic volumes. These measures, based on real-time traffic data, can be used to provide dynamic status information of prevailing network conditions and the “level of service” offered to road-users. Historical data of this kind, including information for incident detection and management and for traffic modelling, can also provide the basis for traffic forecasting and predictive information.
Tree-building algorithms:
Almost all ADMS now include a web-based graphical interface to support users’ queries. The interface is commonly based on Geographic Information Systems (GIS) technology. GIS comprise a set of computer software, hardware, data, and personnel – that store, manipulate, analyse, and present geographically referenced (or spatial) data. GIS can link spatial information on maps (such as roadway alignment) with attribute or tabular data. For example, a GIS-digital map of a road network would be linked to an attribute table that stores information about each road section on the network. This information could include items such as the section ID number, length of section, number of lanes, condition of the pavement surface, or average daily traffic volume. By accessing a specific road segment, a complete array of relevant attribute data becomes available.
The Graphical User Interface (GUI) shown in the ADMS architecture diagram above shows that the data archived in the ADMS can be accessed by different stakeholders over the Internet. Custom applications and reporting functions may be designed including performance measurement, predictive traveller information, traffic simulation model development support, and many other applications.
One of the primary functions of a road or highway network is to allow the safe passage of people and goods from their origin to their destination. Traditional sources of information (printed road maps, direction signs, route listings and journey plans) all have their place but satellite navigation systems are now used widely. Generically these are known as Global Navigation and Satellite Systems (GNSS). Specifically, they include the Global Positioning System (GPS) developed by USA, GLONASS, the Russian global satellite navigation system and GALILEO, the civilian global satellite navigation system being developed by the European Union from its precursor, the European Geostationary Navigation Overlay Service (EGNOS) (See Video).
The USA’s GPS consists of 24 satellites that are deployed and maintained by the US Department of Defence (USDoD). Originally, the system was used solely for military purposes, but since 1983 the USA has made GPS available for civilian purposes. For location determination (longitude, latitude, and elevation), a GPS receiver needs to receive signals from at least four satellites (signals from the fourth satellite are needed to correct for errors and improve accuracy).
A GPS on-board a vehicle – or a smart-phone with a GPS – can determine the location of the vehicle. The location can then be communicated via wireless communication to a central location (such as a traffic operations centre) for processing and data fusion. Besides pinpointing the location of a vehicle and communicating that location to a traffic operations centre, GPS receivers are at the core of all navigation-aid devices developed by companies such as Garmin, TomTom, and Magellan. For navigation and turn-by-turn directions, accurate digital maps are needed, in addition to the GPS receiver.
For its operation, the USA’s GPS relies on signals transmitted from the 24 satellites orbiting the earth at an altitude of 20,200 km. GPS receivers determine the location of a specific point by determining the time it takes for electromagnetic signals to travel from the satellites to the GPS receiver. A limitation of GPS is that it cannot transmit underground or underwater and signals can be significantly degraded or unavailable in urban canyons, in road tunnels and during solar storms. This is why there is continuing interest in terrestrial based radio-positioning systems using technologies such as mobile phones, Bluetooth and Wi-Fi.
GALILEO is the first complete civil positioning system to be developed under civilian control, in contrast to the USA’s GPS and the Russian Glonass systems. GALILEO has been designed with commercial and safety-critical applications in mind, such as self-guided automated cars. The first satellite was launched on 21 October 2011 and the system is scheduled to be fully operational before 2020. When fully deployed GALILEO will consist of 30 satellites (27 operational plus 3 back-up), circling the earth at an orbit altitude of 23,222 km. GALILEO will be fully interoperable with GPS and GLONASS and is expected to achieve very high levels of service reliability and real-time positioning accuracy not previously achieved.
![Figure 3: The European Galileo satellite constellation [European Space Agency]](/sites/rno/files/public/wysiwyg/import/intelligent-transport-systems/1439558854html_html_m763d5216.jpg "Figure 3: The European Galileo satellite constellation [European Space Agency]")
Figure 3: The European Galileo satellite constellation [European Space Agency]
Digital maps are a pre-requisite for satellite navigation and many other ITS applications, such as automated driving and traveller information systems. Many technologies are currently available for creating and updating digital maps. For example, digital maps can be created by collecting raw network data, digitising paper maps, from aerial photographs and other sources. An initiative called OpenStreetMap (http://www.openstreetmap.org) intends to develop digital mapping for the whole world. The maps are developed from GPS traces collected by ordinary people and uploaded to the website. Aerial imagery and low-tech field maps are often used to verify that the resulting maps are accurate and up to date.
A navigation database is a commercially developed database used in satellite navigation systems. It is often based on a Network Gazetteer (See Basic Info-structure) and will contain all the elements needed to construct a travel plan or a route from a specific origin to a specific destination. Additional criteria may be added such as the route passes through a specific point, that it avoids tolls, that it is the fastest or shortest available, or that it minimises fuel consumption or emissions.
A navigation database is multi-layered and requires more than the basic coordinates for the road network links and nodes, although that is an important starting point.
Additional features necessary for navigation include:
Navigation databases also contain information on points of interest and landmarks, such as public transport facilities, major office buildings by name, hotels, restaurants and tourist attractions, post offices, government buildings, military bases, hospitals, schools, petrol stations, convenience stores, shopping centres and malls, toll-booths – and in some countries, the location of speed cameras.
Crowd-sourcing and social networking has enabled the creation of navigation databases that are adapted to the needs of specific groups of road-users, such as truck drivers and cyclists. There are also important developments taking place in pedestrian navigation.
Infromation on pedestrian navigation: http://www.insidegnss.com/node/513 and http://www.navipedia.net/index.php/Pedestrian_Navigation
Location-based services are computer applications that use location data to control features or the information displayed to the user. They have several applications in health, entertainment, mobile commerce, and transport. In road transport, for instance, location-based services can be used to provide point of interest information (using data held in a navigation database – such as the closest fuel station or restaurant. Location-based services can also be used to display congestion or weather information according to the location of the user (See Location-Based Services).
In co-operative systems, vehicles share data with each other and with the road infrastructure using vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) communications. Vehicles that are connected in this way can make use of real-time information on moving objects (such as other vehicles nearby), and on stationary objects that might be transitory (traffic cones, parked vehicles and warning signs). This highly detailed, constantly changing information is held in a data store known as a Local Dynamic Map (LDM). The LDM supports various ITS applications by maintaining information on objects that influence, or are part of, the traffic. Data can be received from a range of different sources such as vehicles, infrastructure units, traffic centres and on-board sensors. The LDM offers mechanisms to grant safe and secure access to this data by means of V2V and V2I communications.
The data structure for the LDM is made of four layers:
Location referencing and object positioning for the upper layers of the LDM is complex and requires adequate location referencing methods. Since not all ITS applications need location referenced information, the use of this data is not mandatory.
These technologies allow the location of vehicles to be ascertained in real-time as they travel across the network. AVL has many useful applications for vehicle fleet management, such as improving emergency management services by helping to locate and dispatch emergency vehicles. AVL can be used for probe vehicle detection and on buses to locate vehicles in real-time and determine their expected arrival time at bus stops.
A number of technologies are available for AVL systems including dead reckoning, ground-based radio, signpost and odometer, and Global Positioning Systems. GPS is currently the most commonly used technology.
Another system for tracking and locating vehicles uses fixed point transponders which can read and communicate with other equipment – for example, toll tags on-board vehicles. These systems can determine when a vehicle passes by a certain point, and provide useful information on travel times and speeds.
A third method for locating vehicles is through mobile phone triangulation. The location of a mobile phone user is identified by measuring the distance to several cell phone towers within whose range the user is located. Using this technology, the location of the vehicle can be identified within an accuracy of about 120 meters. In rural areas, where few cell towers are located, the tower can measure the angle of transmission, which – along with the distance – can be used to locate the phone user even though the user might only be within the range of single cell phone tower. The estimated location in this case is not very accurate (within about 1.6 km).