Road Network Operations
& Intelligent Transport Systems
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Information and Warning

Road users interact with their surrounding environment. Information and safety warnings are provided to drivers during a journey in various ways:

The concept of the “Self-Explaining Road” builds on the interaction of the road user with the environment – by promoting the idea that roads should be understandable to the road user. This is achieved through traffic engineering design supported by clear, consistent and readable roads signs and information to road users to guide them intuitively. Safe design is aimed at encouraging safe road user behaviour.

Modern signing systems have been used since the beginning of the 20th century. Road signs serve a common purpose: to communicate information or provide warnings to road users. Until the 1970s most signs were static. Today dynamic signs are widely used – they exploit information and communication technology and are a key component of ITS as part of the process of bringing together information collection, its integration and dissemination.

Early models of dynamic signs used rotating panels or lamp matrix signs for displaying directional/diversional information or advisory speed limits. More recent models allow greater flexibility in the range of information that can be displayed to road users – such as traffic conditions, incident warnings and road safety campaign messages.

One of the main purposes of dynamic signs is for traffic management – to manage incidents and mitigate their impact – by providing warnings of incidents and diversion advice and regulating traffic flow through variable speed limits. (See Use of VMS)

There are three major groups of stakeholders in the provision of safety information and warnings across the road network:

  • road owners, operators and traffic police who are responsible for infrastructure provision and everyday operation of highways and road networks
  • equipment manufacturers and suppliers, who must respond to specifications and design guidelines, the practicalities of operating a road network and the needs of road users including their likely perception and behaviour
  • road users themselves, who need to be able to easily interpret the information and warnings – and therefore need to be consulted on the design of signs and messages.

Design Considerations

There are several aspects to the design of information signs and warning systems for the road operators to take into account before putting in place solutions to specific problems:

  • information overload
  • driver awareness, attention demands and level of compliance
  • design of text based dynamic signs
  • standardisation

Information overload refers to the situation where there are too many signs along a stretch of road or at a single location. Dynamic signs may provide advantages over static sign if the display can be turned off when not needed (for example weather related warnings for ice or flooding). They can also be made to activate on detection of an approaching vehicle – usually in response to excess speed to get the attention of the individual driver.

Driver awareness of messages and their compliance can vary considerably and are influenced by the content of the message, its context and the road user’s previous experiences. Poor management of information signs can lead to lack of confidence – for example failure to remove a warning message when a traffic incident has cleared.

Driver attention is affected by the format of the display. Text messages tend to require greater levels of attention than symbols or pictograms. Drivers generally have a preference for pictograms although they are not necessarily always understood. Signs which change in real-time also impose higher attention demands compared to fixed signs. Readability and comprehensibility are affected also by the content of the message and how it is formatted. Splitting a long message into two short lines instead of one can shorten the response time – as can using a two-coloured display.

Design of text based dynamic signs is constrained by the limited space available which constrains the length of the message. Drivers tend to read messages in a series of short glances. The time frame available between first seeing the message and passing by may be quite short, even at low speeds. Prevailing driving conditions will influence how much attention the driver is able to give to reading and understanding the message.

Standardisation of static signs has been developed over a long period beginning with the Geneva Convention on the Unification of Road Signals, 1931. Dynamic signs, by contrast, are not yet standardised to the same extent – at either the national or international level.

Queue Warnings

Queue warnings are an effective contribution to managing traffic on high speed roads. They serve three objectives:

  • to avoid rear-end collisions when traffic is required to slow down and queues begin to form
  • to protect against secondary collisions when the traffic ahead is stationery following a collision
  • to divert traffic away from an incident that blocks the highway to prevent queues from becoming longer by re-routing traffic across the local and regional road network

Effective queue warnings for network management require:

  • real-time monitoring of traffic flow and vehicle speeds
  • advance warning of the queue appropriate to the traffic situation which relates to traffic flow and highway capacity (for example, “Queue Ahead” displayed on VMS two miles ahead);
  • advisory messages over a wide area, of disruption, to enable drivers to re-route their journeys if necessary (See En-route Information)
  • prompt cancellation of warning messages – the display of out of date message affects driver confidence and trust in warning systems

Queue warning systems therefore rely on rapid incident detection and warning technologies which:

  • automatically detect abnormal flows and speeds – for example by means of camera-based image processing systems, induction loops or above ground sensors
  • enable visual confirmation of automated detection systems using traffic surveillance cameras
  • activate warning messages on dynamic signs (automatically or manually by traffic control room operators)
  • activate variable speed limits where appropriate (automatically or manually by traffic control room operators)
  • activate diversions where appropriate (in some cases this is done automatically or more often, manually by traffic control room operators with reference to a traffic management plan) (See Traffic Management Plans)

In addition to road-based solutions, automotive manufacturers are developing collision warning systems that make use of on-board radar and sensors to detect obstacles (such as stationary vehicles ahead) to warn the driver or activate autonomous braking.

Cooperative vehicle systems communications - car to car (C2C) or car to infrastructure (C2I) - are able to warn drivers well ahead of an incident or queues forming (See Warning and Control Systems).

Further Information

Queue warning systems (See

Portable End-of-Queue Warning Systems (See

Broken-down Vehicle Warning

The reason for deploying broken-down vehicle warning systems is to prevent rear-end collision and secondary collisions. They follow similar principles and use similar technologies as queue warning systems:

  • incident detection to provide warnings to drivers using dynamic message signs and to activate variable speed limits
  • in-vehicle forward collision warning systems
  • Dynamic Lane Merge Systems (DLMS) which make use of dynamic signs to facilitate vehicle merging at the approach to lane closures

eCall is a European collision notification system aimed at summoning rapid assistance to motorists involved in a collision anywhere in the European Union countries. It uses GPS and digital cell-phone communications (such as GSM) to automatically initiate a 112 emergency call  to  the nearest emergency centre. It transmits the exact geographic location of the accident scene and other data. Such services are valuable for saving lives – in particular for single vehicle accidents in rural/remote areas. (See and DRIVE C2X project

Further Information

Breakdown Safety Strategy: A way forward. September 2012. Transport for NSW, Australia. (See



Road-side animal detection systems are deployed in some countries to prevent crashes involving large animals. There are potential dangers from free roaming cattle, wild horses, elephants, moose, kangaroos, bears and reindeer. The systems alert drivers to potential collisions with animals and rely on radar, lasers and other imaging techniques to detect the presence of animals on the roadway.

There are broadly two approaches to detection:

  • area sensors that register the presence of large animals within a certain range using infrared light or microwave radio signals – and which can be enhanced with algorithms to distinguish between animals and other moving objects in order to avoid a false detection
  • break-the-beam sensors which respond when an animal crosses the beam between a transmitter and receiver. The beam can be infrared, laser or microwave radio signals

False alarms are the main problem, triggered by wind, rain or overgrown vegetation. Sensors can be adjusted, but it is very difficult eliminate false alarms completely whilst still ensuring that the target animals are detected. The frequency of false alarms should be monitored and adjustments made to the detection sensitivity of sensors – for example in advance of adverse weather conditions or in different seasons.

Further Information

Sharafsaleh, M. and Huijser, M. (2012) Evaluation of an animal warning system effectiveness. California PATH, Richmond, CA, USA. Report number UCB-ITS-PRR-2012-12. (See

Ontario Ministry of Transportation, Canada. (See

Bozeman Pass Wildlife Linkage and Channelization and Highway Safety Studies (See



Reference sources

Megan Bayly, Brian Fildes, Michael Regan, Kristie Young (2007) Review of Crash Effectiveness of Intelligent Transport Systems (See