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.

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:

• the complete road network geometry, which must be regularly updated
• a full and complete functional classification of the roads
• toll roads
• freeways/ expressways
• major urban arterial roads
• main streets
• residential streets
• low access streets (private roads, unpaved roads)
• accurate information on street and highway interconnections
• details of all motorway overpasses and underpasses
• road characteristics, including one-way information, turn restrictions, divided lanes, number of lanes and lane-use restrictions, stop lights, stop signs and construction status
• street, village, town and city names and alternative (alias) names where appropriate
• address ranges for both sides of the street
• postal location codes (postcodes, ZIP codes)
• "vanity" names for buildings and locations as well as the postal address

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.

Further information

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:

• the first layer stores the static map information. This is data about the road network, provided by a map data supplier, that is permanent
• the second layer extends the static map with information that is important for co-operative systems – for example road signs, intersection features and landmarks for referencing and positioning
• the third layer contains information that is dynamic and transient, such as weather, traffic attributes and road conditions
• the top layer contains highly dynamic information about the position of vehicles and road users – detected by in-vehicle and other sensors. It also keeps track of the available communication nodes. This fourth layer is particularly important for Connected Vehicle applications

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.

Fixed point transponder-based systems

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.

Mobile phone triangulation

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).

Traffic detectors (or vehicle presence detectors) are used in many ITS applications for – network monitoring, traffic control, speed measurement and automatic incident detection. Many different types of detection technologies are available. The following are typical technologies that have been developed to measure traffic data in specific locations and zones. (See Vehicle Detection)

Inductive Loop Detectors (ILD)

Inductive loop detectors are currently the most widely used devices for vehicle detection, although microwave radar detection is also common. Their main uses are at intersections in conjunction with advanced signal traffic control systems, and on freeways for traffic monitoring and incident detection purposes. ILDs typically take the form of one or more turns of insulted wire embedded in the pavement. The loop is connected via lead-in cable to the detector unit, which detects changes in the loop inductance (changes in the in the magnetic field of the sensor) when a vehicle passes over it. ILDs can be used to detect a vehicle’s presence or passage. They can also be used to measure speed (by using two loops a short distance apart) and for classification of vehicle types. The main problem with using ILDs, however, is their reliability. Because ILDs are subject to the stress of traffic, they tend to fail quite frequently. Moreover, their installation and maintenance require lane closure and modifications to the pavement.

Inductive Loop Detectors

Microwave Radar Detectors

Microwave radar detectors are examples of non-intrusive detection devices whose installation and maintenance does NOT require lane closure and pavement modifications. Unlike inductive loops, non-intrusive detection devices are not embedded in the pavement. Instead, they are typically mounted on a structure over, or to the side of, the road such as the radar detection system in the photograph below.  Depending on the type of electromagnetic wave used, microwave radar detectors can measure either vehicle presence, or vehicle presence as well as speed. They are also widely used to detect pedestrians waiting at pedestrian crossings.

One of the major advantages of microwave sensors is their ability to function under all weather conditions. Exceptions can be extreme weather such as sand-storms. Given that these sensors are installed above the pavement surface, they are not typically subject to the effects of ice and ploughing activities. Experience shows that microwave sensors function adequately under rain, fog, snow, windy conditions. Their main problem is that they can be obscured by tall sided vehicles – reducing their accuracy when they are installed at the side of the carriageway.

Non-intrusive Traffic Detector (Image courtesy of the IBI Group)

Infrared Sensors

Infrared (IR) sensors are also non-intrusive detection devices. There are two types: passive and active detectors.

Passive IR detectors do not transmit energy – instead, they detect the energy that is emitted or reflected from vehicles, road surfaces and other objects. Passive infrared detectors can measure speed, vehicle length, vehicle counts and occupancy but their accuracy is affected by adverse weather conditions.

Active IR detectors emit a beam of Infrared energy which is reflected back to an IR receiver. They function in a similar way to microwave radar detectors – by directing a narrow beam of energy towards the road surface. The beam is then reflected back to the sensors – and vehicles are detected through changes in the “round-trip” transmission time of the infrared beam. Active infrared detectors supply vehicle passage, presence, speed, and vehicles classification information. They work well in controlled environments such as tunnels – and infrared can be used for safety purposes to detect over-heating vehicles or fire. Their accuracy is affected by weather conditions such as fog and precipitation.

Ultrasonic Detectors

Ultrasonic vehicle detectors function in a similar way to microwave detectors by actively transmitting pressure waves, at frequencies above the human audible range. These detectors can measure volume, occupancy, speed, and classification. Ultrasonic sensors are sensitive to environmental conditions. They require a high level of skill for their maintenance.

Acoustic Detectors

Vehicle traffic produces acoustic energy or audible sound from a variety of sources within the vehicle and from the interaction of the vehicle’s tyres with the road surface. Using a system of microphones, acoustic detectors are designed to pick-up these sounds from a specific area within a lane on a roadway. When a vehicle passes through the detection zone, a signal-processing algorithm detects an increase in sound energy and a vehicle presence signal is generated. When the vehicle leaves the detection zone, the sound energy decreases below the detection threshold and the vehicle presence signal ends. Acoustic sensors can be used to measure speed, volume, carriageway occupancy and presence. The advantage of acoustic sensors is that they can function under all lighting conditions and during adverse weather.

Magnetometers

Similar to inductive loop detectors (ILD), magnetometers provide for point detection, but they differ from ILD in that they measure changes in the earth’s magnetic field resulting from the presence of vehicles. They can provide information on traffic volume, lane occupancy, speed as well as vehicle length. In general, there are two types of magnetometers:

• micro loops which are installed in the pavement in a similar way as ILDs
• wireless magnetometers

Micro loops, (like inductive loops), require lane closure and pavement modification, with consequent delays to traffic. In recent years, the use of wireless magnetometers has received increased interest because of advances in battery technology which allow a unit to operate wirelessly for a period of 10 years before needing to be replaced.

Videos:

Traffic Detector Video Training Course - Part 1 - Detector Theory

Traffic Detector Video Training Course - Part 2 - Detector Design

Traffic Detector Video Training Course - Part 3 - Detector Installation

Traffic Detector Video Training Course - Part 4 - Detector Maintenance

AVI can be used to identify vehicles as they pass through a detection zone. Typically, a transponder (or a tag) mounted on the vehicle can be read by a roadside reader as the vehicle passes by. This information can then be transmitted to a central computer. Currently, the most common road transport application of AVI technologies is in combination with Automatic Toll Collection systems (such as EZPass). With these systems, the value of the toll is automatically deducted from a driver’s account each time the driver goes through the toll plaza.

Automatic Number Plate Recognition (ANPR) Systems

An important method of AVI, in common use, are ANPR (also known as Automatic Licence Plate Recognition - ALPR) systems which use optical character recognition technologies to identify and recognise vehicle registration plates. They typically consist of a specially adapted video camera linked to character recognition software. As a vehicle passes an ANPR/ALPR camera its registration number is read and can be checked against a database of vehicle records. There are two broad types of ANPR/ALPR systems:

• those that perform all the optical character recognition (OCR) processes in the field in real-time
• those that transmit the images to a remote computer for OCR processing

With recent advances in computer hardware and software – processing in the field in real-time has become quite feasible (it typically takes less than 250 milliseconds). This avoids the cost associated with the need for large bandwidth to transfer images to a remote server.

Weigh-in-motion sensors are designed to measure and record axle weights and gross vehicle weights while the vehicle is in motion (driving – not stopped). WIM systems are attractive because they avoid the need to stop and weigh every vehicle. They have not eliminated the need for weighbridge sites for accurate weighing of trucks, but WIM acts as a filter and only vehicles which register an excess axle load need to be stopped and checked. The key component of any WIM system is the force sensor – for example quartz crystals produce electric charge when a force is applied along the vertical axis (the weight of the vehicle). WIM systems have several applications in ITS, especially as a part of an electronic pre-clearance system for commercial vehicles, as well as for enforcement applications. (See Enforcement and See Video)

Further Information

http://www.worldhighways.com/categories/traffic-focus-highway-management/features/weigh-in-motion-and-anpr-techology-aid-highway-protection/

Speed detection is an integral part of speed camera enforcement systems used to detect speed-related violations of traffic rules especially at accident hot spots. (See Speed Management) Regulation of speed is important at work zones where personnel are at increased risk of an accident. It is also a feature of active traffic management schemes on motorways. Some speed enforcement systems automatically link speed cameras to vehicle number-plate (Licence-plate) recognition for issuing enforcement notices. (See Traffic Management and Integrated Strategies) Speed detection can also be used as a safety measure at signalised intersections on fast arterial roads by using microprocessors to extend the green time at traffic signals when a vehicle is approaching at speed.

For measuring speed, the most common device is a radar meter or sensor which uses the Doppler principle. Specifically, the device measures the difference in the emitted and reflected frequency of a radar wave – which is proportional to the speed of the moving object. Other types of vehicle sensors can be adapted in pairs to measure speeds – such as ultrasonic sensors and magnetometers.

Journey time monitoring is related to speed monitoring. Vehicle journey times are significant sources of information for network performance monitoring and advising road users about travel delays in real-time. They are a measure of the level of service on offer. Some road authorities display point-to-point journey times on roadside VMS as a form of real-time information. Journey time data (historic and in real-time) is also a useful resource for journey planning and logistics support. (See Journey Time Monitoring)

Travel Times and Speed over Distance

Various methods are available to anonymously track vehicles on the network and enable network operators to determine average travel times, point-to-point demand and traffic flow conditions. For example, Automatic Toll Collection (ATC) systems can be used to determine the average travel time on highways between toll collection plazas or specially installed roadside readers. Infra-red (IR) tag-equipped vehicles are used as probes for monitoring traffic flow conditions – which are detected by transponder readers, installed along roadways. Aggregate data on average speeds and travel times can be compiled and this helps support incident and traffic management. To protect travellers’ privacy, these systems scramble the toll tag identifiers and only keep records of trips made by anonymous vehicles.

A number of other techniques are used to provide continuous, non-invasive, point-to-point tracking of individual vehicles to determine travel times and calculate average speeds. They include automatic number-plate recognition cameras (ANPR cameras) to identify vehicle licence plates. A new development is point-to-point monitoring of Bluetooth signatures emitted by equipment present in the vehicle. Bluetooth sensors have been used successfully for point-to-point average speed monitoring as a cheaper alternative to ANPR. Some road authorities use aggregated data (made anonymous) to display on VMS to provide drivers with expected journey times between key points on the network.

Environmental sensors are used in road network monitoring to detect adverse weather conditions such as icy or slippery conditions, high winds or precipitation (snow or rain) or the presence of fog/mist. This information can then be used by operators to alert drivers via variable message signs (VMS). It can also be used by highway maintenance personnel to optimise winter maintenance operations. (See Weather Monitoring)

Environmental sensors can be divided into six types:

• road condition sensors that measure surface temperature, surface moisture, and presence of snow accumulations
• visibility sensors that detect fog, smog, dust clouds, heavy rain, and snow storms
• thermal mapping sensors that can be used to detect the presence of ice
• anemometers to detect wind speed
• air quality sensors to monitor pollution levels
• noise sensors to measure traffic noise levels

Many manufacturers provide complete weather station systems that are capable of monitoring a wide range of environmental and surface conditions. The figure below shows one example of these weather stations.

(Figure 4.7 to be located here – to be supplied by the author)

Weather stations typically include the following types of sensors and capabilities:

Road condition sensors: A critical component of any road weather information system (or RWIS) is a set of road condition sensors that measure surface temperature and moisture, and detect the presence and thickness of snow and ice. Road condition sensors can be embedded in the pavements. They can also be non-intrusive – mounted to side or above the road surface. Non-intrusive road condition sensors typically measure the emitted infrared radiation from the road surface.

Visibility sensors: These sensors are designed to measure visibility along a road section. They typically use the principle of “forward scattering” or diffraction of light to detect changes in visibility resulting from inclement weather conditions such as fog, haze, and smoke. The sensors need to be carefully sited because they can only provide spot measures at a specific location. For example, fog detectors need to be sited as near as possible to the source where mist or fog forms first.

Thermal mapping: Given that temperatures can vary significantly along a roadway segment, thermal (temperature) mapping sensors are typically a critical component of an effective ice detection system. Thermal mapping provides road operators with information on road-surface temperatures to inform decision making on the need to set-up warning messages on VMS or to deploy snow clearance, road salting and gritting services. Examples of thermal imaging sensors include thermal imaging cameras/ video and infrared thermography.

Wind speed sensors: These are an essential component of an environmental sensing station and are installed at high and exposed bridges and windy locations on the road network. They typically measure surface wind speed and direction and can be used to provide warnings to vehicles towing trailers and high-sided vehicles. For safety reasons it is sometimes necessary to close the road in high winds.

Cell phones are a very effective tool for incident detection. Many regions have established an incident reporting hotline to encourage citizens to report traffic incidents. This has the advantage of low start-up costs.

Anonymous Mobile Call Sampling

The widespread use of cell phones can provide useful traffic information. Triangulation techniques can determine a vehicle’s position by measuring signals from an on-board cellular phone within the vehicle. To enable this, the cell phone needs to be communicating with more than one cell-phone cell – preferably three or more for accuracy – so that triangulation can take place. Each phone is typically identified by its electronic serial number. This concept was first tested in the Washington D.C. area in the mid 1990s. This concept is different from GPS-based AVI systems in which the GPS unit on the phone determines the location, which is then communicated from the phone to a central processing system.

Emergency Roadside Telephones (ERTs) were regularly provided prior to mobile telephones becoming widely available. ERTs still provide a valuable service where there is a low ownership of mobile telephones or a mobile-phone black spot. They provide an accurate location to the operator of where a caller is located and enable stranded motorists to call for help. More generally, they allow travellers to report incidents such as accidents or stray animals on the carriageway.

To use a call box, the motorist just needs to lift the receiver or press a key to request the services of the police or emergency services. The caller is automatically connected to a control room operator.

Advanced types of ERTs provide background noise cancellation against traffic noise, and a simple question and answer facility based around «yes» and «no» keys for the profoundly deaf and foreign travellers. The Operator has a formal list of questions that they can ask in sequence by typing in the questions. The questions appear on a small screen at the ERT and the user answers using the yes and no keys. The option to select different languages is a great advantage near ports and border crossings where there is a high percentage of foreign visitors. They also have a call-back facility that enables the operator to call the stranded motorist, with a beacon and ring tone to attract attention.

Typically, the phones are located on the side of the freeway, and are spaced at distances ranging from 0.25 miles to 0.50 miles apart. On all-purpose dual carriageway arterial roads, freeways and motorways they need to be located in pairs on either side of the road to avoid travellers being tempted to cross the road to use one.

(Figure 4.5 Call Box – Image to be provided by Barry Moore)

These are teams of trained officers who are responsible for covering a given segment of the freeway. Mobile patrols have a central part to play in road network operations, spotting debris on the road, dealing with incidents and the general public. A freeway service patrol vehicle [Figure 4.6] is typically equipped to be able to help stranded motorists and, where possible, to clear an incident site. Mobile patrols are capable not only of responding to incidents, but in some cases to perform the entire incident management process (from detection to clear-up).

Technology, in the form of secure mobile communications and hand-held tablets, provides support. TETRA mobile radio communications offer digital transmission capability whilst maintaining the advantages of a Private Mobile Radio (PMR) system. In future service patrols may have command and control capability to direct and manage the deployment of on-road resources – and the potential to set VMS and signals on location, remotely from the road side.

Figure 4.6 A Freeway Service Patrol Vehicle

A relatively new technique for collecting traffic-related information based on mobile reports is crowdsourcing – using social networks such as Facebook and Twitter. Crowdsourcing is the process of obtaining information online that is provided by a crowd of people. This method has become feasible in recent years because of the significant developments in positioning and communications technologies that are linked to mobile phones which have internet connectivity. In road transport, crowdsourcing concept can be used to collect vital travel-related information in collaboration with members of a community. One of the most famous and successful of these crowd-sourcing applications is WAZE (https://www.waze.com/) – one of the world's largest community-based traffic and navigation apps. Users of WAZE share real-time traffic information, allowing members of the on-line community to save time and fuel while travelling.

Vehicles are used to report journey times and detect traffic incidents – monitoring their progress in time and space. This can be done by either using automatic vehicle location systems or by tracking the progress of identified vehicles between known fixed points on the network. The location of the vehicle in time and space is communicated to a central computer where data from different sources is fused to determine the status of traffic flow over the transport system.

Vehicle probes can provide very useful information that other detection techniques cannot – including information on link travel times, average speeds, and origin-destination information.

Different technologies are available. These include:

• Automatic Vehicle Identification (AVI);
• Automatic Vehicle Location (AVL);
• Anonymous Mobile Call Sampling;
• Bluetooth and Wi-Fi Networks.

Vehicle probe methods give more reliable but less dense data than crowd-sourcing, which may provide better geographical coverage. Vehicle probes are often deployed by road network operators in collaboration with the owners of vehicle fleets that regularly travel the network.

Video image processing (VIP) identifies vehicles and their associated traffic flow parameters by analysing imagery supplied from CCTV cameras which normally have a fixed field of view. The addition of VIP significantly improves the usefulness of CCTV, particularly where there are a large number of cameras installed, which an operator cannot view at the same time. VIP also provides the means for alerting operators to a traffic incident.

Analogue CCTV images are digitised and then passed through a series of algorithms that identify changes in the image background. In modern digital cameras the video image is already in a digital form – ready for processing. A VIP system consists of a video camera (a digitiser in the case of analogue cameras) and a microprocessor for processing the digital-image – and software to interpret the image content and extract detection information from it.

VIP for Traffic Detection

With digital processing CCTV provides an above-ground alternative to inductive loops or other means of vehicle detection. One big advantage of VIP systems is their ability to provide detection over a number of lanes and in multiple zones within the lane – providing wide area detection. The user can easily modify the detection zones, within seconds, through the graphical interface – without the need to close traffic lanes and dig-up the pavement. Poor lighting, shadows, and bad weather can negatively affect the performance of VIP systems. Evaluation studies in Oakland County, Michigan indicate that modern VIP systems yield excellent performance with a detection accuracy of over 96% under all weather conditions.

VIP for Incident Detection

VIP systems can be combined with CCTV systems to provide an excellent detection tool, particularly for incident detection and verification purposes. When an incident occurs, the user can switch from the VIP mode to the standard CCTV mode, and then verify the occurrence of the incident via pan/tilt/zoom controls.

Dynamic Message Signs are also referred to as Variable Message Signs and Changeable Message Signs. In this website the following terminology is used:

• Dynamic Message Sign (DMS) refers to any sign or graphics board where the message (text or pictogram) conveyed to the viewer can change.

A DMS may be either a Variable Message Sign (VMS) or Changeable Message Signs (CMS) where:

• VMS is a sign capable of displaying pre-defined or freely programmable messages which can be changed remotely, namely with individual pixel control;
• CMS is a sign capable of displaying pre-defined fixed messages which cannot be changed remotely;
• A Portable Dynamic Message Sign is referred to as a PDMS.

DMS are among the most common types of devices for information provision. They can either be fixed  or portable as shown below. They can be text-based, graphics based or a combination of the two (See Traffic Management)

Figure 4.12 Fixed Dynamic Message Signs

Figure 4.13 Portable Dynamic Message Signs

DMS can be used to provide travellers with instructions such as closed lanes or recommended speeds and information on traffic and weather conditions, incident locations and expected delays, construction work, alternative routes and speed advisories. Different types of DMS can be light-reflecting, light-emitting, and hybrid according to the technology used. Light emitting diodes (LEDs) are generally the preferred option where there is a power supply (including solar options).

Light-reflecting signs

As the name suggests, these rely on an external source of light, such as the sun, headlights, or overhead lighting, to make them visible – by reflecting the light source. Different types of light-reflecting signs include rotating drum and reflective disk matrix signs. Rotating plank/drum signs are made of one to four multi-faced drums, each containing two to six fixed text messages or graphics. The main application of rotating plank/drum technology when it is incorporated into a fixed direction sign – is to provide variable instructions, that are identical in appearance to the fixed sign face, to show an alternative direction to a destination.

Reflective disk matrix signs comprise an array of permanently magnetised, pivoted indicators that are black on one side, and reflective white or yellow on the other. When a specific pixel is activated, an electric current flips the indicator from the black finish to the reflective yellow finish.

Reflective disk matrix signs were popular in 1970s for freeway management systems because they were less costly than light-emitting signs. Mechanical failure of some or the entire message is common (disk failure). As LED signs become less costly the older technology is falling out of use.

Light-emitting signs

These generate their own light on or behind the viewing surface – either in monochrome or full colour. Light emitting diode (LED) and fibre-optic DMS are two examples:

• where LED are used to create display pixels they are typically amber in colour – although full-colour and white LED display panels are now coming into use;
• fibre-optic DMS funnel light energy from a light source through fibre bundles to the sign face.

LED has become the preferred technology. New versions of LED DMS provide a display known as a full matrix that can display graphics and images.

Hybrid DMS combine the characteristics of both light-reflecting and light-emitting DMSs. One of the best examples of hybrid DMSs is the reflective disks/fibre-optic or LED DMS. During weather conditions when light-reflecting DMS are not clearly visible, these hybrid systems can use light-emitting technologies such as fibre-optics or LED. When the sun is shining, the light sources are turned off. Solid state LEDs are more reliable than reflective disks since there is no risk of mechanical failure.

In-road markers or lane lights (also known as intelligent road studs) can be used to convey important messages to drivers, in addition to their most direct function of lighting the way at night. For example, in-road markers can be used to communicate the usage of a lane. Intelligent road studs have been used for signing the use of the hard shoulder during periods of heavy congestion, hazard warnings and operation of part-time bus lanes

These devices are typically located inside the vehicle and, similar to DMS, are designed to provide information to drivers while en-route. In-vehicle information devices can provide information by either audio or visual means. Examples of auditory in-vehicle information devices include highway advisory radio (HAR), cellular phone hotlines and commercial radio. Examples of visual in-vehicle devices include video display devices and head-up displays (which drivers can read without altering their normal viewing position

Highway Advisory Radio

Highway advisory radio (HAR) provides another means for disseminating information to drivers while en-route. Typically, information is provided through an AM receiver. Drivers are informed about the existence of an HAR signal by signs which are typically installed upstream of the signal, advising drivers to tune in to a specific frequency (typically either 530 kHz or 1610 kHz) (See Radio).

HAR can be used to provide travellers with information similar to that provided by VMS. One advantage of HAR compared to VMS is that it is less distracting – since information is provided through a different sensory channel (audio) which reduces visual information overload. More complex messages are also possible with HAR compared to DMS. The disadvantage is that users have to tune to the frequency themselves.

Cellular Telephone Hotlines

Another way of providing information to drivers en-route, – which has increased in popularity with the widespread use of cellular phones – involves establishing a “hotline” phone system for traffic information that drivers can call from their cell phones while en-route (such as the 511 system in the US). The phone systems typically include a touch-tone menu that allows callers to receive route-specific traffic information – this gives the driver control over the type of information received.

AUDIO: Local radio

Commercial radio is another means of providing en-route traveller information. The primary disadvantage of commercial radio is the accuracy and timeliness of the information. Typically, information is broadcast only when normal scheduling permits – and in many cases, this may be inappropriate since an incident might have been cleared by the time normal scheduling permits broadcasting.

Video and Head-up Display Terminals

A recent approach to disseminating traffic information en-route involves the use of dashboard displays, video and head-up display terminals. Close attention to the design of the Human-Machine Interface is needed to minimise driver distraction (See Human Factors).

These technologies are widely used for pre-trip and off-roadway information dissemination. They include cable TV, phone systems, the internet, pagers, smart phones and tablet computers. Many metropolitan areas around the globe now have websites dedicated to traveller information. These systems provide travellers with a wealth of travel-related information, including current travel conditions, alerts, and other timely information. A traffic map showing current speeds, locations of any incidents or construction zones typically form a central part of these websites. Among the technologies used for off-road roadway information dissemination are dynamic public information displays and kiosks – and mobile devices.

Dynamic Public Information Displays and Kiosks

Large shopping malls and motorways often have dynamic information displays and kiosks where real-time travel conditions may be provided. This is also true of many motorway rest areas. These displays and kiosks were very helpful before widespread public take-up of mobile computing devices and smart phones. With the advent of these technologies, public information displays and kiosks have played a secondary role in information dissemination. They are still available at many sites and are useful for those sectors of the population who do not have access to mobile computing and smart phones.

Mobile Devices

The high market penetration of smart phones, tablet computers and personal navigation devices has provided the transport industry with an invaluable tool for disseminating travel information. The unique advantage of these nomadic and mobile devices is that they make travel information available to travellers on a continuous and uninterrupted basis.

Many navigational devices and services include real-time information about the transport network conditions. This is demonstrated by services such as Google maps and navigation – as well as by GPS navigation devices that can receive real-time traffic condition information. Crowd-sourcing is also being used to collect and disseminate travel information.

Point-to-point microwave communication uses ground-based transmitters and receivers resembling satellite dishes to provided dedicated backhaul links where landlines would impractical or prohibitively expenses to connect roadside networks to a control center. They are usually in the low-gigahertz range and limited to line of sight. Repeater stations can be spaced at approximately 48 km intervals to cover greater distances.

Wi-Fi has become a very popular technology for the exchange of data wirelessly using radio waves over a computer network. Wi-Fi can support non-critical ITS applications because it avoids delay – but does not have bandwidth guarantees. Wi-Fi operates using unlicensed frequencies – so are more susceptible to interference. The technology has potential for use in ITS as a means for connecting field devices to a Traffic Control Centre – for example, where a wired communications solution would be too expensive. In this case, a secure Wi-Fi connection, such as the wifi-mesh network shown in the figure below would need to be provided. This shows a multipoint to multipoint WiFi Mesh network suitable for VMS, car park counters, traffic signals, remote monitoring and non-enforcement CCTV.

Wi-Fi is based on the Institute of Electrical and Electronics Engineers’ (IEEE) (IEEE) Standard 802.11. It is designed to provide local network access over relatively short distances (between 50 – 100 meters) with speeds of up to 54 Mbits/second.

Figure 6 Diagram of a wifi-mesh network suitable for highway data transmission

(Figure courtesy of Barry Moore)

Bluetooth

Bluetooth technology also supports data exchange over short distances. It uses short-wavelength ultra-high frequency (UHF) radio waves. Bluetooth technologies are used in many different applications such as smart phones, headsets, tablets and laptop computers. Recently, there has been increased interest in building on the presence, on-board vehicles, of Bluetooth devices in “discoverable” modes, to track and monitor traffic. These applications use roadside Bluetooth detectors to discover Bluetooth devices on-board the vehicles and detect their unique identifier. By tracking the same identifier through different location points, important traffic parameters can be determined such as travel time, speed, vehicle origin and destination.

Another group of communications technologies widely used in ITS is dedicated short-range communications (DSRC). DSRC was developed specifically for vehicular communications and is likely to witness a dramatic increase in use with the introduction of Connected Vehicle technologies. The technologies are used in a number of ITS applications including:

• electronic payment for parking and tolls;
• commercial vehicle pre clearance;
• bus and emergency vehicle signal priority;
• in-vehicle signage;
• probe vehicle data collection;
• highway-rail intersection warning;
• intersection collision avoidance;
• vehicle-to-vehicle cooperative systems such as Adaptive Cruise Control (ACC) and Forward Collision Warning (FCW).

In the USA, DSRC generally refers to communications on a dedicated 5.9GHz frequency band reserved specifically for Wireless Access in Vehicular Environment (WAVE) protocols – defined in the IEEE 1609 standard and its subsidiary parts. These protocols are based on the widely-used IEEE 802.11 standard for Wi-Fi wireless networking.

Several DSRC technologies are used in transportation. These include:

Passive microwave (tag & beacon)

Passive tags do not have an internal power supply. Instead, they use the very small electrical current induced in the antenna by the incoming radio frequency signal, to transmit a response. For this reason, the antenna has to be designed not only to collect power from the incoming signal, but also to transmit the outbound backscatter signal. The main advantage of passive microwave tags is that they can be quite small and have an unlimited life. Passive microwave was used in ITS for early types of electronic toll collection systems. Innovations in their use continue.

Active microwave (IEEE 802.11/WAVE)

Active tags have their own internal power source which can generate the outgoing signal. Compared to passive tags, they may have a longer range and can store additional information sent by the transceiver. Active microwave is employed in many electronic toll collection systems. More expensive on-board units have batteries which need replacing.

Infra-red (DSRC)

Infra-red DSRC uses infra-red technology, as opposed to radio spectrum or microwave, for short-range communications. Infra-red DSRC can be used in ITS where it is difficult to secure a frequency spectrum license. The technology is also appropriate when the weather is generally rainy – but not foggy. Infra-red DSRC is less susceptible to security intercepts.

Bluetooth is a wireless technology designed to allow data exchange over short distances (a maximum of about 10 meters). Most cell phones on the market today have Bluetooth technology. They also have Wi-Fi wireless technology, which uses radio waves for connections for distances to a Wi-Fi base station of up to 90 meters. In recent years, several automotive manufacturers have been embedding Bluetooth technology into their vehicles to allow drivers to connect their phones or music devices to in-vehicle audio systems.

When activated, Bluetooth and Wi-Fi transceivers continuously broadcast “discovery” messages to allow other devices to find and connect with them. The discovery messages include a unique identifier that can be used for vehicle detection and tracking. Essentially, all that is needed is a Bluetooth or Wi-Fi sensor installed close to the roadway. These sensors record the time at which a a vehicle equipped with an on-board Bluetooth or Wi-Fi device drives past them. By utilising the unique identifiers recorded at successive monitoring points, information on travel times along a road segment – or the pattern of Origin-Destination flows through a network – can be derived.

The use of Bluetooth or Wi-Fi is ideal for crowd sourcing but the results have to be calibrated as:

not all vehicles report an identifier – since some will not be equipped with the technology or the equipment may be turned off – leading, in both cases, to no count being registered

or a single vehicle may have several active devices – leading to multiple counts.

When using this vehicle sampling technique a key challenge is to ensure that a sufficiently high proportion of vehicles are equipped with Bluetooth and Wi-Fi devices. In urban areas, this may not be a major concern, but in other regions low market penetration may limit the application of these detection technologies.

Communications over a wide area are often required in Network Operations – particularly in rural areas where the options for voice and data communications and the transmission of CCTV images are more limited.

WiMax

WiMax stands for Worldwide Interoperability for Microwave Access. WiMax is designed to provide much higher bandwidth, compared to Wi-Fi, and at a much extended range. Recent years have seen increased interest from the ITS industry in integrating WiMax and Wi-Fi as an alternative communications medium to wired communications.

Under ideal conditions, WiMax could have a range of more than 40 kilometres, and offer speeds of up to 70 Mbits/seconds. It implements the IEEE 802.16 Standard, with newer standards designed for speeds of up to 1 Gbits/second. A typical WiMax network would consist of a base station connected to several client radios (Customer Premise Equipment or CPE).

Cellular Data

Cellular networks were established primarily for voice communications, but there is steadily growing increased interest in their use for data communications as well. Two voice communication cellular technologies have evolved in this way:

Global System for Mobiles (GSM)

Code Division Multiple Access (CDMA)

They differ in the way they transfer data. GSM divides the frequency band into multiple channels for use by different users. CDMA digitises calls and unpacks them at the back end. Both GSM and CDMA have been refined and enhanced over the years to allow for increased speed. For example GPRS (for packet data communications) uses the GSM cellular network at speeds suitable for transmitting commands to VMS and car park counters.

The latest cellular data technology is Long Term Evolution (LTE) (also known as 4G LTE). Unlike GSM and CDMA, LTE is designed primarily for data communications, with voice as an override. It offers high bandwidth, low latency, and supports full data rates while travelling at high speeds (a feature which is important in the ITS environment with fast-moving vehicles). Cellular data communications can be used in ITS where wireline communications are not available or are cost-prohibitive.

Digital Radio Data

Digital Radio Data (DRT) refers to the practice of transmitting digitised and compressed data over FM radio. This allows small amounts of digital information to be embedded in conventional FM radio broadcasts. A good example of a DRT application in ITS is the Radio Data System-Traffic Message Channel (RDS-TMC), where digitally encoded traffic information is made available for in-vehicle navigation devices. RDS-TMC is an early form of digital data transmission. It was developed in Europe to exploit the Radio Data System used by some broadcasting authorities. Travel information is transmitted digitally over FM radio frequencies – and a decoder, built into the car radio or navigation device, interprets the digital code for text or graphic display.

Spread Spectrum Radio

Spread spectrum radio is a radio network that has a “line-of-sight” requirement (unobstructed line of path between a subject and an object). In this network, one radio serves as the master and the other as slave. An example of the use of spread spectrum radio in ITS is the connection between a set of traffic controllers at signalised intersections and the Traffic Management Centre (TMC) needed for monitoring and signal timing purposes.

In some cases, it might not be possible to directly link the two radios because of distance or interference – in which case another radio (called a repeater) would need to be installed in-between the two radios. These networks are most commonly used to allow a number of traffic controllers to communicate with one another, or to communicate with a traffic operations centre. They can broadcast over the unlicensed frequencies of 900MHz, 2.4 GHz and 5.8 GHz. The 5.8 GHz frequency provides the highest bandwidth at about 54 Mbits/second, but is very susceptible to line-of-sight problems.

Whilst theoretically, spread spectrum radio can provide a communication range of up to 60 miles, in practice the range is much shorter because of line of sight attenuation or obstructions.

Computer signal control systems first appeared in the 1960s when computers were first used to coordinate the traffic signal controllers for a group of intersections – but without the benefit of today’s “feedback” of information from the field detectors to the computers. In this type of system (known as open-loop control) the traffic plans that are implemented are not responsive to actual traffic demand. Instead, plans are developed “off-line” using data from historical traffic counts – and implemented according to time-of-the-day and the day of the week.

This system is quite basic, but it still offers several advantages including:

• the ability to update signal plans from a central location – greatly facilitating implementation of new signal timing plans as the need arises;
• the ability to store a large number of signal plans – that can be implemented depending on prevailing traffic conditions;
• automatic detection of any malfunction in the operation of the controllers or the signal heads.

The next level of sophistication is signal control systems where information from field traffic detectors is fed-back to the central computer. The computer uses the information on current traffic conditions to select the signal plan to be implemented (closed loop control). Plan selection is made according to one of the following methods.

Select a Plan from a Library of Pre-developed Plans

Here, the system has access to a database (library) that stores a large number of different traffic patterns along with the “optimal” signal plans (developed off-line) for each traffic pattern. Based upon information received from the traffic detectors, the computer matches the observed traffic pattern to patterns stored in the library, to identify the most similar pattern. The “optimal” plan associated with the identified pattern is then implemented. This type of adaptive traffic control system is often referred to as a First Generation system. Its distinguishing feature is that the plans, while responsive to traffic conditions, are still developed off-line. First Generation systems work on the basis of current traffic data and do not generally have traffic prediction capabilities.

Develop Plan On-line

In this method, the “optimal” signal plan is computed and implemented in real-time. The optimal signal timings are computed in real-time using current data on traffic conditions obtained from detector information. This requires sufficient computational power to make the necessary computations on-line. It also needs enough data from the vehicle detectors to make the calculations. The systems that develop plans on-line are classified as either Second-Generation or Third-Generation systems. They typically have a much shorter plan update frequency compared to First-Generation systems, typically every 5 minutes for Second-Generation systems, and from 3 to 5 minutes for Third-Generation systems. In addition, some Third-Generation systems use forecasts of traffic conditions obtained from feeding the detector information into a short-term traffic-forecasting algorithm.

There are a number of examples of adaptive traffic control systems in use around the world. Amongst the most widely accepted algorithms are SCOOT, SCATS and RHODES.

SCOOT

SCOOT (Split, Cycle, Offset Optimisation Technique) is an adaptive traffic control system developed by the United Kingdom’s Transport Research Laboratory (TRL) in the early 1980s. SCOOT operates by attempting to minimise a performance index (PI) – typically, the sum of the average queue length and the number of stops across the controlled network. In order to do this, SCOOT modifies the length of the cycle, the amount of green time given to each signal phase (known as the time “splits”), and the offset time for each set of signals (the time difference between the cycle start times at adjacent signals). SCOOT computes these calculations in real-time in response to the information provided by vehicle detectors.

The operation of SCOOT is based upon Cyclic Flow Profiles (CFP). These are presented as histograms (graphical representations of user-specified ranges) that show the variation in traffic-flow over a cycle – which is measured by loops and detectors that are placed midblock on every significant link in the network. Using the CFPs, the offset optimiser calculates the queues at the stop-line. The optimal splits and cycle length are then computed.

Several additional features have been added to SCOOT to improve its effectiveness and flexibility, including the ability to:

• provide signal priority for public transport (transit) vehicles;
• automatically detect the occurrence of incidents;
• add-on an automatic traffic information database to feed historical data into SCOOT – enabling the model to run even if there are faulty detectors.

SCATS

The Sydney Co-ordinated Adaptive Traffic System (SCATS) was developed in the late 1970s by the Roads and Traffic Authority of New South Wales in Australia. For operation, SCATS only requires stop-line traffic detection, not the midblock traffic detection that is necessary for SCOOT. This simplifies installation since the majority of existing signal systems are equipped with sensors only at stop-lines. SCATS is a distributed intelligence, hierarchical system that optimises cycle length, phase intervals (splits), and offsets in response to detected volumes. For control, the network of signals is divided into a large number of smaller subsystems, each ranging from one to ten intersections. The subsystems run individually unless traffic conditions require the “marriage” – or the integration – of the individual subsystems.

RHODES

Since 1991, the University of Arizona has been developing a real-time adaptive control system called RHODES, which stands for Real-time Hierarchical Distributed Effective System. RHODES is designed to take advantage of the natural stochastic (random) variations in traffic flow, to improve performance – a feature which is missing from systems such as SCOOT and SCATS.

The RHODES system consists of a three-level hierarchy that decomposes the traffic control problem into three components: network loading, network flow control and intersection control:

• at the highest level, a stochastic traffic equilibrium model is used to predict expected traffic loads on the links of the network;
• the second level, Level 2, represents the high-level decision-making process for setting signal timing to optimise traffic flow. This recognises the unpredictable (stochastic) nature of traffic and attempts to take into account future expected traffic loads over the next few minutes. Level 2 is concerned with setting approximate phase sequences and splits for a given corridor (target timings).

Level 3 is concerned with intersection control – determining the optimal time to change traffic signals for the next phase sequence and whether the current phase should be shortened or extended. The time frame for control level 3 is typically in the order of seconds and minutes.

Where there alternative routes available the problem of optimising traffic on the network can be tackled mathematically. For dynamic route guidance (DRG) the “objective function” (an equation expressing the operational function that needs to be maximised or minimised) – is the measure of the highway network’s performance that needs to be optimised. For example the objective might be to minimise the total travel time for all vehicles. The decision variables are the proportions of traffic that splits at each diversion point – to optimise network performance. The traffic-splits define how traffic should be distributed. The aim is to model traffic flow in the region and ensure that it is maintained at the nodes and along the links of the network, without congestion setting in. ITS software can then be used to solve the problem of optimising the objective function and recommending a routing strategy that will vary in real-time according to traffic conditions. Routing advice will be given in traffic broadcasts and on VMS, or with in-vehicle route guidance for those vehicles that are equipped.

Public transport priority (known as Transit Signal Priority or TSP in the USA) is a measure aimed at reducing delay for public transport vehicles (buses, trams, taxis) at signalised intersections by giving their movements preferential treatment. The methods for doing this can be divided into passive and active strategies. The basic difference is whether specialised sensors and detectors are used to detect approaching public transport vehicles. Without supporting technologies to specifically identify these type of vehicles, passive TSP technology simply improves conditions for all vehicles along a public transport corridor.

Active technologies detect an approaching bus or tram (this is typically accomplished by having a transmitter on the vehicle that communicates with a receiver or detector on the roadside signal controller). Different algorithms or strategies are available for active bus priority. Amongst the most common are:

Green Extension: this extends the green time if a bus or tram is detected, to allow the priority vehicle to pass – up to a certain pre-determined limit. This strategy only benefits a small portion of vehicles, but the reduction in delay for beneficiaries is significant (equal to the length of the whole red interval)

Early Green: shortens the green time for conflicting phases, by a pre-defined amount of time – for example when the bus arrives whilst the traffic light is in its red phase. Early green benefits a large percentage of buses, but the saving per vehicle is not as large as for Green Extension

Phase Rotation: under this strategy, the sequence of green time for different manoeuvres at the intersection is changed so that the priority vehicle is not held up. One common modification – that allows the vehicle to cross the opposing traffic stream – involves swapping a dedicated turn signal at the start of the cycle (the “leading” phase) to the end of the cycle (the “lagging” phase).

Actuated Transit Phase(s): involves establishing transit phases, which are only active when a bus/tram is present. In this case, a special transit signal face would display, for example, a letter “B” for Bus or “T” for Tram.

Phase Insertion: this allows the same phase to appear more than once during the same cycle in order to serve the transit vehicle.

The OBE are:

• the equipment inside the vehicle with which the drivers will interact;
• and the technologies needed to provide vehicle-based information for use within CV applications.

Some of the vehicle-based information can be obtained from GPS or other similar sensors (for example location, speed, and direction), whereas other information (for example acceleration, instantaneous fuel consumption, anti-lock brakes activation, wiper status) may be obtained from vehicle engine scanning tools and other systems monitoring the vehicle’s different subsystems.

Connected vehicles are instrumented with a wide range of sensor technologies to enable applications aimed at improving safety and efficiency – including:

• position sensors such as GPS or Inertial Navigation Systems (INS)
• speed and braking sensors;
• vehicle proximity sensors that can also measure the distance or headway between the subject vehicle and the car in front or behind;
• sensors able to detect sleepy or incapacitated drivers (these typically use video cameras and sophisticated video image processing/pattern recognition algorithms);
• near-and far-distance obstacle detection sensors based on either LIDAR (LIght Detection And Ranging) or radar technologies to identify hazardous situations or imminent collisions – to warn the driver and take evasive actions to prevent the collision.

Roadside units and equipment are infrastructure systems that communicate with vehicles and collect data from the vehicle. Roadside equipment can support infrastructure-based applications – or applications involving co-operation between vehicles and the infrastructure (such as intersection collision avoidance systems, and eco-signals which inform approaching vehicles about the remaining green-light time to enable drivers to adjust their speed). Roadside equipment also supports remote applications by communicating information collected from the vehicles to a central location for processing. They also may help support the security and integrity of cooperative vehicle systems.

The communications network is the infrastructure needed to provide connectivity between vehicles (V2V), between vehicles and the infrastructure (V2I), and between roadside equipment and other parts of the system (V2X). Wireless communications are required for V2V and V2I communications, whereas roadside equipment may use wireless or wired networks.