2. Guidelines for Variable Message Sign Control

Document No:  D10#43935
Revision:  2
Date amended:  11-Mar-2010

Image: orange line.RCN-D13^23151823.GIF The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Bita Charehjoo by e-mail or on (08) 9323 4439.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.


Revision Register

Ed/Version NumberClause NumberDescription of RevisionDate
  1 All Guideline Developed 08-Jul-2009 
  2 All Guideline Revised 11-Mar-2010


Table of Content


Variable Message signs (VMS) are also known as Dynamic Message Signs (DMS) or Changeable Message Signs (CMS). Main Roads has adopted the term Variable Message Signs.

VMS are a primary means of communication between the Main Roads Traffic Operation Centre (TOC) and the driver. They provide an effective tool to manage traffic in response to incident management, special events and construction and maintenance activities.

Under normal traffic conditions, the VMS sign is either blank or contains a generic message such as safe driving advice, the distance to the next exit or current speed on a specific road. When drivers are to be warned of an emergency, advised to change routes, or guided to a particular location, an appropriate message is posted. The credibility of these signs is critical; hence an accurate message should be displayed on each sign.


This guideline does not provide model designs or even a step-by-step process to ensure an effective outcome. Instead it identifies the various elements which need to be taken into consideration, and to provide guidance on how each of these should be addressed.


TOC - the Main Roads Traffic Operation Centre operates 24 hours, seven days a week throughout the year. The centre provides traffic monitoring information, emergency response and manages traffic related incidents when they occur.

MRWA - Main Roads Western Australia

VMS - Variable Message Sign

ITS - Intelligent Transport System

COMMUNICATION PROTOCOL - Software and Hardware technology applied to communicate a message to and from the variable message sign to the Traffic Operation Centre.

UPS - Uninterrupted Power Supply


The Policy comprises three parts:

  • Selection and Posting of VMS messages
  • Locality of VMS
  • Users Policy.
4.1 Policy on Selection and Posting of VMS Messages

The policy on selection and posting of VMS message identifies the requirement under each project and the selection of appropriate messages for individual incidents and events. 

4.1.1 Effective Message Display

For a VMS message to be effective, it shall:

  1. Fulfil a need.
  2. Command attention.
  3. Send a clear and simple message.
  4. Command respect from road users.
  5. Provide adequate time for proper response time.
  6. Use same message for the same incident regardless of location of incident.

 4.1.2 VMS Application

A VMS should be used if:

  1. Drivers are expected to take a particular action.
  2. The message is considered critical.
  3. The message accuracy has been confirmed by a reliable source.
  4. Conditions can be monitored so that the sign can be updated as soon as events allow.
  5. The message does not tell drivers something that is already obvious.

 4.1.3 Credible Message Display

A VMS should be updated if:

  1. A change in driver's behaviour is no longer required.
  2. The message accuracy is questionable.
  3. The information on the sign is obvious.
  4. Too many drivers are ignoring the information.
  5. The amount of delay changes significantly.
  6. The recommended alternate route changes.

 4.1.4 Message Display System

VMS status displays must be designed to promote easy interpretation and strategic understanding of system status. This is especially true when multiple operators may be responsible for VMS operations. Hence, the following requirements shall be adhered to.


4.1.5 Automated Message Posting

The goal for a VMS management support system is to provide a fully automated message posting, with capability for the operator to modify messages after they are posted.

Automated posting of VMS incident messages should be based on all available data, from both automated sensors and human sources. Many automated VMS systems use traffic flow data to detect potential incidents and establish response plans for VMS posting.

 4.1.6 Operator Message Posting and Control

Higher reliability is required when the automated support system uses operator verification data, and any additions or modifications to traffic flow data are required to be  entered by the operator. Even with automated posting of VMS responses, the operators should maintain situation awareness of the status of VMS assets.

The operators must be provided with a resource map that shows the location and status of all sensors, cameras, VMSs, and other TOC resources. It should indicate whether each VMS sign is currently in use. Before implementing a response plan for a specific incident, all related signs should be checked to ensure that they are not displaying an important earlier message for a different incident. On any status map of a divided highway, display unambiguously the direction of travel on which the incident is located.

4.1.7 Interactive Message Posting System

Provide an easy way for the operator to modify or discontinue a VMS response plan or individual message that is no longer appropriate. To maintain public trust in the VMS system, messages must be timely and accurate. To support this requirement, modification or discontinuation of a message must be easy for the operator and thus reduce the possibility that this task will be "shed" during times of high workload. The approach shall be a computer interface in which a mouse "click" on a VMS sign on the map display would bring up a screen menu. This menu would provide, at a minimum, alternatives to "MODIFY" or to "DELETE" the message on that sign.

The visual display shall enable  Main Roads staff to know at any time, what symbol is being displayed on the sign and, if required, to subsequently use this information in a court of law. This technology overcomes the problems of bulb changing associated with the halogen type signs as well as offering more flexible display options.




Canning Highway VMS.JPG 

Canning Highway VMS


South Street VMS.JPG 

South Street VMS

4.2 Policy on Locality of VMS

Notwithstanding the legibility sight distance requirements, all VMSs should be placed so they are clearly legible to all road users and every effort should be made to reduce competition with other traffic signs or roadside furniture. VMS should not be placed in locations where they will be partially hidden by other traffic signs, roadside furniture and vegetation.

 4.2.1 Decision Points

VMS should not be permitted within an interchange area or in close proximity to an off-ramp or on-ramp where merging, frequent braking or weaving movements are common. The VMS location should:

  • Make allowance for the drivers' response and reaction time so that they can correctly respond to the  displayed messages on the VMS,
  • Be compatible with other static signs in the area to enable drivers to make decisions based on all conveyed information.

 4.2.2 Spacing of VMS

VMS on the Freeway / Highway network must be positioned so that road users have time to respond to the messages provided and therefore should be positioned an adequate distance in advance of major decision points. Generally major decision points are off-ramps that will be used for diversions such as those defined in incident Management Plans.

4.3 VMS Users Policy

The designer should contact Main Roads Traffic Operation Centre (TOC) to obtain a copy of the VMS Users Policy.


Typical message types include:
5.1 Traffic Management
  • Road closures
  • Road works
  • Traffic delays
  • Real time and travel time data

5.2 Emergency and Incident Management

  • Road accidents
  • Road closures
  • Fire
5.3 Environmental Condition
  • Flood
  • Cyclone
  • Heavy rain
  • High speed wind
5.4 Event Management
  • New Years eve
  • National days like Australia Day, Anzac Day
  • Triathlon
  • City to Surf
  • Christmas pageant
5.5 Road Safety Messages and Messages of Public Interest
  • Road safety slogans
  • Community benefit messages
  • Public Transport information


6.1 Standards

The VMS shall be selected in accordance with Australian Standards:

  • AS4852.1 Variable message signs - Fixed signs
  • AS4852.2 Variable message signs - Portable signs

and shall be compatible with existing technology.

6.2 Specific Technical Requirements for Selecting VMS

The VMS selection shall be in accordance with the design brief and listed requirements and will typically:

  • Have the option to be a flexible multicolour display - Red, Amber, Green or White.
  • Control motorway applications for allowing variable speed limits.
  • Have optical feedback for legal enforcement.
  • Have LED based technology.
  • Require low maintenance frequency.
  • Perform to Australian Standards and Main Roads specifications.
  • Include applications like lane control signals - Lane use signals - Variable speed limit signs.
  • Include wind speed sensor to adjust travelling speed.
  • Have backup power supply. Battery to be operational for minimum of 12 hours. Refer to Main Roads Specification 713 Installation of UPS.
  • Be available in standard size format in accordance with Australian Standards AS 4852.1-2009 and AS 4852.2-2009. 
  • Be fully programmable with at least two colour LED matrix.
  • Have capability to interface with all Main Roads existing software protocols.
  • Have an identification number specific to each sign and readable by the road user.
  • Allow for generation of double stroke thickness characters.
  • The capability to automatically 'move around' a displayed image on the VMS in a regular, timed mode to extend pixel life.
  • Allow ability to check for pixel failures.
  • Allow for fully automated ambient light responsive dimming.
6.3 Selection of VMS Board

The VMS shall be selected such that it suits

  • The type of road,
  • Design / posted  speed,
  • Environment,
  • The location of the VMS within the road reserve.

The VMS shall be selected in accordance with the project Scope and shall comply with following arrangements:

  • One-Line Signs
  • Two-Lines Signs
  • Thee-Lines Signs
  • Four-Lines Signs

Type B VMS has the ability to display up to three rows of 18 characters.
Mini VMS has the ability to display up to three rows of 9 characters.

6.4 Selection of Portable or Fixed Variable Message Sign

Variable Message signs shall be selected in accordance with Projects specific requirements and deliverables and conform to one of the listed types below:

  • Fixed Overhead sign
  • Fixed Road side sign
  • Portable Trailer and Vehicle Mounted sign



The signs shall be separated at a distance in accordance with Sign requirements to allow drivers to read and understand the message in advance of the decision points. The distance shall be calculated based on the posted speed and the time required for the driver to read and understand the message.

VMS sites should generally be located on straight roadway sections. Where curves in the roadway are present on approach to the proposed VMS location, consideration should be given to the angle at which the VMS will be located.

It is desirable that a VMS be located 900 - 1200 m before each Freeway on-ramp and off-ramp point (primary exits, but median breaks should also be considered if they are likely to form part of an Incident Management Plan).

VMS spacing between exit points on the Freeway and Highway network should be located between 3000 to 5000 m but need to be considered in line with the approved Incident Management Plans.

For Urban arterial roads, it is considered that VMS should be positioned 400 - 700 m prior to a major intersection, offering alternative routes.

7.1 Sign Visibility

The sign shall be clearly legible in all lighting conditions and shall be located well in advance of decision point and take into account factors including obstructions and observation angle. The sign size, and font type and size, must be appropriate for the posted speed on the road and shall be in accordance with Australian Standards 4852.1-2009, AS 4852.2-2009 and AS1742.

7.2 Road Geometry

7.2.1 Horizontal Geometry

Avoid positioning a VMS immediately before and after a sharp bend, blind crest, decision point, merge point or at the intersection where the VMS may distract attention at a critical moment  where it could lead to loss of control of the vehicle.

The VMS must not be positioned where the display may be seen from a neighbouring road as this results in motorists receiving conflicting information.

To ensure proper viewing of the VMS, it should be located on straight sections of the road. The introduction of VMS on tight curves can impact visibility due to the limitations in the current pixel technology.

7.2.2 Vertical Geometry

Vertical alignment along the roadway also has impacts on the visibility of the VMS. If there are a limited number of potential locations available, a flat or rising grade of 1% will provide a preferred option for sign location. VMS should not be placed where grades exceed 4%.

Consideration should also be given to obstacles such as bridges, gantries, vegetation etc that may impact on the line of sight to VMS. It is essential that available sight distance is based on the posted speed limit of the road. The size of VMS should be selected on the basis that adequate distance is available to allow drivers enough time to read and respond to the message displayed.

Vertical clearance to the gantry structure supporting the VMS panel needs to comply with the minimum clearance stipulated by the Main Roads Heavy Vehicle Operations Branch.

7.3 Vertical and Horizontal Clearances

The designer shall allow for clearances required for High Wide Load corridor and envelopes when selecting mounting height and the clear zone required for the VMS Structure Location. VMS support structures should be located beyond the clear zone or be shielded by a suitable safety barrier.

7.4 Location of Power and Communication Facilities
Site location must provide for safe maintenance and operation of the VMS and the controller cabinet. Safe and easy access to the sign for maintenance crews/vehicles must be ensured.
7.5 Proximity to other signs

The VMS should not compete with other existing signs or interfere with traffic control devices. When considering suitable locations an inventory of all signs and traffic control devices in the vicinity of the preferred location/s should be taken. Based on this inventory existing signs may need to be moved to accommodate the most effective VMS placement.

The following should be considered:

  • In general, it is desirable that VMS are located at least 200 - 300 m from major static Freeway directional signs.
  • However, it is understood that this requirement may be difficult to achieve in an urban situation and a distance equivalent to 0.6V should be used as a minimum spacing to signs on urban arterial roads.
7.6 Design Objectives
  • Sight distance including proximity to other visual obstruction.
  • Allowing adequate manoeuvring time
  • Location of sign in relation to decision point.
  • Location of sign with respect to its proximity to a change in road alignment such as merge and lane zones or on a change of horizontal or vertical geometry. 
  • Proximity of VMS to roadside items and furniture, such as static signs, light poles, traffic control device and vegetation
  • Provide clear legibility to all drivers.



8.1 VMS Communication Protocol

Ensure that the VMS is compatible and operational with existing VMS Software and communication technologies available at the Main Roads Traffic Operations Centre (TOC).

Installation of Variable Message signs shall be completed in accordance with the Manufacturer's specifications and Main Roads Specification 704. The commissioned sign shall be compatible with Main Roads current communication protocols.

8.2 Selection of Hardware and Communication Protocol
The selected VMS and all connections shall be in accordance with Main Roads current practice and existing hardware. For further details contact the Asset Manager of Traffic Systems on 9323 4171.
8.3 VMS Programming Requirements

The VMS shall be able to be controlled and monitored from both a local and remote position, and shall be fully site addressable.

The following definitions for VMS sign operation are used.

FRAME - a single display of one or more lines of alpha-numeric characters or graphics images (and/or a combination of both) at one time.

MESSAGE - a combination of up to 6 frames in sequence with variable timing for each sequence or translation.

PLAN - a combination of frames and/or message strings with defined start, finish and operation times.

The existing storage of PLAN data as modified for this upgrade, shall at least comply with the following:

  • (a) 255 or more individual frames.
  • (b) 255 or more messages.
  • (c) 255 or more plans.

The display of messages by enabled plans shall be based on priority levels. More urgent displays shall override 'usual' display plans.

High priority messages shall initiate and retain the flashing amber displays on the sign corners (facility to be added under this project).

The information about frames, messages and plans shall reside locally in the sign and at the TOC. Checksums shall be used to ensure the equivalent stored data is identical at both locations.

The local control system shall be able to load into memory a schedule of display programs which are implemented based on the local real time clock (including day-of-week) which is accurate to within +/- 1 second per week. The VMS real time clock shall be routinely (and automatically) synchronised with the central control system clock.

The system shall include a full complement of test programs suitable for routine servicing or fault maintenance capable of displaying all standard modes, and for the purpose of identifying faults.

8.4 Font Type and Height

The characters and lines shall have sufficient spacing between them to allow for ease of legibility. Higher speed areas obviously require larger character sizes in order to provide suitable legibility distances.

Character fonts shall be proportionally spaced except for a single non-proportional font.

The following fonts shall be defined for the sign:

  • Font 1 - Fixed font based on 5 x 7 matrix.
  • Font 2 - Proportional font.
  • Font 3 - Bold (double stroke) proportional font 1.
  • Font 4 - Double line proportional font (11, 12, 14 and 16 pixels high).
  • Font 5 - Large font (25 pixels high).

All characters of all fonts shall be spaced with 2 pixels between characters, and 3 pixels between lines of characters.

The sign shall be in accordance with

  • AS1742, Manual of uniform traffic control devices set
  • AS1744, Forms of letters and numerals for road signs
  • AS4852.1, Variable message signs - Fixed signs
  • AS4852.2, Variable message signs - Portable signs
8.5 Programming Standards

The software development process shall comply with the following standards:

  • HB 90.9:2000 - Software Development Guide to ISO 9001:2000
  • AS 3930:Reliability & Maintainability - Introductory guide
  • AS 3960:  Guide to reliability and maintainability program management
  • AS/NZS  ISO/IEC  12207: Information technology - software life cycle processes
  • AS 4006: Software test documentation
  • AS 4009: Software reviews and audits
  • AS 4042: Software configuration management plans
  • AS 4043: Software configuration management



Abbreviations can be used to avoid using extra characters when the abbreviation meaning is clearly understood or implied. For example,

FWY = Freeway
HWY = Highway
RD = Road

For current list of acceptable abbreviated messages and complete messages refer to the Main Roads Traffic Operations Centre - VMS User Policy.



Procedures must ensure appropriate coordination between signs in order to avoid displaying contradictory information.



Australian Standard AS 4852.1-2009, Variable message signs. Part 1: Fixed signs.

Australian Standard AS 4852.2-2009, Variable message signs. Part 2: Portable signs.

British Columbia Ministry of Transportation, BC MoT Guidelines for the Operation of Changeable Message Signs (CMSs) and Portable Changeable Message Signs (PCMSs), Sep. 6th 2006.

CDOT Guidelines On Variable Message Signs, Colorado Department of Transportation, VMS Committee, Feb 2005.

Guidelines for Changeable Message Sign (CMS) Use, British Columbia Ministry of Transportation, Sept 15 2000.

Guidelines for the Location and Placement of Variable Message Signs, RTA Technical Direction, TDT 2005/02, March 2005.

LTN 1/09 signal controlled roundabouts, TEC April 2009

Main Roads (Control of Advertisements) Regulations 1996

Main Roads ITS Supply and Installation Specification, ITS-02 Variable Message Signs, Oct 05 (Rev 1)

Main Roads VMS Users Policy

VMS Guidelines and Reference Manual, Transit New Zealand, Version 11 December 2006.