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Road Network Operations
& Intelligent Transport Systems
A guide for practitioners!
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:
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 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 are an effective contribution to managing traffic on high speed roads. They serve three objectives:
Effective queue warnings for network management require:
Queue warning systems therefore rely on rapid incident detection and warning technologies which:
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).
Queue warning systems (See http://mobility.tamu.edu/mip/strategies-pdfs/active-traffic/executive-summary/queue-warning-1-pg.pdf)
Portable End-of-Queue Warning Systems (See http://tti.tamu.edu/enhanced-project/facilitating-deployment-decisions-of-highly-portable-end-of-queue-warning-systems/)
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:
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 http://www.heero-pilot.eu/view/en/ecall.html and DRIVE C2X project http://www.drive-c2x.eu/use-03)
Breakdown Safety Strategy: A way forward. September 2012. Transport for NSW, Australia. (See http://www.mynrma.com.au/media/rms_breakdown_safety_strategy.pdf)
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:
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.
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 http://www.dot.ca.gov/newtech/researchreports/reports/2012/2012-06_task_2090-tsm.pdf)
Ontario Ministry of Transportation, Canada. (See http://www.mto.gov.on.ca/english/safety/wildlife.shtml)
Bozeman Pass Wildlife Linkage and Channelization and Highway Safety Studies (See http://www.mdt.mt.gov/research/projects/env/boz_wildlife.shtml)