Road Network Operators and other transport or public safety professional have no direct control over road users (except, perhaps, at traffic signals). Each road user is an independent entity that observes situations from the perspective of his or her specific needs, does their own thinking and decision making and executes their decisions more or less independently. The only thing the transport profession can do is to inform the travellers in the best possible manner to enable them to make informed – and hopefully safe – decisions. (See Traveller Information Systems )
A survey by Florida DOT District 6 (Miami-Dade Co. and south) found that 92% of freeway/turnpike drivers read VMSs at least weekly, 97% said these signs provide accurate traffic alerts, and 78% reported a willingness to alter their route based on VMS postings. Use of 511 increased in the past year and 22% of respondents were more willing to change their departure time as a result of 511 information.
(Source: Rodriquez, J., “Miami Drivers Reported Travel Benefits from Using Dynamic Message Signs,” SunGuide® Disseminator, Florida DOT, January 2013.)
Advanced Traveller Information Systems, or ATIS are designed to support individual decision-making. The goal of ATIS is for travellers to have information at their disposal to help them make better-informed travel decisions about mode, route, departure time and activity choices. A side effect of these better decisions can often be supportive of efficient and safe traffic operations.
There is a full range of advanced traveller information provider systems and services. A summary is given in th table below along with advantages and disadvantages (in no particular order):
Technology |
Advantages |
Disadvantages |
Posting of messages on VMSs |
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Posting of messages on PDMSs |
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511 (voice, automated) |
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Call taker |
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Website (TCC or 511) |
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Media – radio traffic reports |
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Media – TV traffic reports |
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Airborne spotting and reporting |
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Kiosks and display signs |
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In recent years, the proliferation of smartphones and other mobile devices (such as digital tablets and pads), the expanding use of social media and the increasingly wide-spread use of Floating Vehicle Data collection techniques have led to a number of truly advanced traveller information services. Some services collect data to be used by other traveller information providers.The Table below summarises these.
Technology |
Advantages |
Disadvantages |
Point (that is, fixed location) data collection systems |
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Floating (probe) vehicle tracking |
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Commercial traveller information services |
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Social media – situation reporting |
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E-mail alerts |
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In-vehicle telematics (including personal navigation devices) |
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VMS and Highway Advisory Radio (HAR) are used to alert rural travellers in mountainous areas about weather and other conditions on the roadway ahead.
On long-distance or international trips, applications like those mentioned above (as applicable) or kiosks at rest areas, can help these long-distance travellers either adjust their trip plans or at least have a more secure feeling about their trips. (See Kiosks)
Traveller information in the other modes can do such things as inform public transport passengers of the arrival of the next vehicle and provide transfer information. Whilst these do not directly impact traffic operations at that time, this type of traveller information makes travellers more comfortable and confident about using public transport, thereby encouraging them to continue to do so and not add to clogging the roadways with more cars. Some Integrated Corridor Management (ICM) concepts include public transport as well, particularly Bus Rapid Transit (BRT) systems.
Traveller information can also provide information that does not directly affect current travel, but serves other purposes, such as safety messages, smog alerts and for child-kidnapping alerts. Note that there is some debate about the use of VMSs and HAR for non-mission-critical purposes. (See En-route Information)
There is a great deal of potential benefit that can be derived from using third-party data services (for example, real-time journey times on VMS, website traffic information, conducting historical analyses and so on). A number of commercial traffic Independent Service Providers (ISPs) provide services to both individual travellers and businesses as follows:
Further information: See Travel Information Systems and Traveller Services
Variable Message Signs (VMS) are capable of displaying pre-defined or freely programmable messages which can be changed remotely with individual pixel control. They consist of:
A Dynamic Message Sign (DMS) is any sign or graphics board that can change the message (text or pictogram) conveyed to the viewer. It may be either a Variable Message Sign (VMS) or a Changeable Message Sign (CMS) where:
See Roadside DMS
Roadside and overhead VMS are a basic traffic management tool for road owners and authorities – to provide information and advice to drivers and riders independent of any in-vehicle systems. In some cases VMS signs can replace fixed roadside signs to inform drivers of speed limits – if necessary with the flexibility of changing mandatory speed limits in response to traffic or road conditions where the legislation allows.
Research evidence shows that road user acceptance and compliance is substantially increased when the reason for a new, lower than normal, speed limit is displayed on the VMS in addition to the prevailing speed limit.
VMS can be used to convey maximum advisory (non-mandatory) speeds — to advise drivers and riders to slow down in fog, high winds and icy conditions or on the approach to an incident or slow-moving traffic ahead.
Evaluation of an icy road surface warning system installed on a mountain road in California indicated that, when the warnings of icy conditions were activated, mean speeds were more than 5 mph (8 km/h) lower than when no warnings were shown (Veneziano and Ye, 2011). In specific situations where ice was present but not likely to be expected by drivers (such as cold, clear and not-dry conditions), the reduction in speed was somewhat less — under 3 mph to around 3 mph (4.8 km/h). The speed data was collected at the VMS sign – rather than in the subsequent curve where the driver response may have been greater.
A fog-warning system on the A16 in the Netherlands had two levels of lower speed limit available, depending on the level of visibility. It was found that when the system was activated, average speeds decreased by 9-10 km/h. When the very low visibility speed limit was displayed, average speeds were higher than appropriate for the road conditions indicating that the advisory speed limit of 60 km/h was not low enough to influence driver behaviour sufficiently.
Dynamic management of speed limits in response to traffic flows has been shown to reduce speed variability and smooth flows, reduce numbers of accidents and increase overall throughput. It also has environmental benefits through the reduction of emissions. It is mainly applied on motorways. When used in construction zones or for temporary narrow lanes, the safety impacts are considerable, particularly as regards the protection of roadside workers. Dynamic speed limits are often combined with camera-based speed enforcement. (See Work Zones)
Roadside VMS is commonly used, particularly on urban roads, to inform drivers that they are speeding in the hope of encouraging them to slow down. These VMS are linked to speed detectors. When triggered by a speeding vehicle they display the speed limit or a message such as “Slow down”. The devices can also be mounted on a trailer for portability – for use, for example, in work zones. Portable Dynamic Message Signs (PDMS) have been shown to have an effect on the proportion of drivers speeding and on average traffic speeds. Some of that impact may be a novelty effect — since few evaluations have looked at the persistence of changes.
“Smart” or “Managed” motorways are becoming more common as a means of managing high traffic flows on motorways. (See for example http://www.highways.gov.uk/our-road-network/managing-our-roads/improving-our-network/smart-motorways/).
Typically, as traffic builds up towards the critical 2,000 vehicle per lane per hour, speed limits are reduced. The aim is to reduce speed variance and shock waves caused by traffic slowing down and speeding up - which can lead to incidents and accidents. The overall objective is to maintain traffic throughput - but the schemes have also brought about reductions in accidents and secondary incidents. Speed limits are enforced with automatic camera-based technology (time over distance cameras in the more recent schemes). Another common feature is the use of the hard shoulder for traffic at times of high congestion (“hard shoulder running”) with appropriate VMS signing. (See Case Study: Active Traffic Management Pilot M42 (UK))
National and regional standards are likely to apply to the design and installation of VMS. There are also applicable international standards for regulatory signs. Sixty three countries across the world have ratified the Vienna Convention on Road Signs and Signals. This states that road signs conveyed on VMS should generally conform to the text and symbols used on standard road signs. The Convention allows variations in colour in the interests of legibility. For example, it permits the use of dark text on a light background (the norm for speed signs) to be replaced by light text on dark background in the case of VMS - although the border must remain red.