Policy Instruments

Variable Message Signs
SummaryFirst principles assesmentEvidence on performancePolicy contributionComplementary instrumentsReferences


Variable Message Signs (VMS) are digital road signs used to inform car drivers about specific temporary events and real-time traffic conditions. The signs are often linked to a manned control centre via a local network or a radio link. Variable message signs (VMS) are an integral part of Intelligent Transportation Systems.

The aim of using VMS is to provide drivers with mandatory and/or advisory information at the roadside. VMS can be used for many different purposes with the potential benefits of reducing car drivers’ stress, travel time and increasing traffic safety. VMS may ask drivers to change travel speed, change lanes, divert to a different route, direct to the available parking space, or simply to be aware of a change in current or future traffic conditions by providing information. The information is intended to assist drivers in selecting appropriate routes avoiding congestion and to reduce drivers’ anxiety.

The benefits of the signs in general are difficult to measure. VMS are often used to inform drivers of congestion, incidents ahead and unexpected delays and can as such reduce drivers’ stress. Signs can be particularly beneficial where drivers can be informed of alternative routes or park and ride sites to avoid further delays, but this may require the VMS to be an integral part of a wider and more costly traffic monitoring system. One major study suggests that drivers would like to see VMS used more. Clear facts seem to exist that VMS are not likely to distract drivers if designed properly. A reduction in the number of violations of speed limits can be expected where ‘SLOW DOWN’ signs are put up. While as yet there is little firm evidence of the safety benefits of VMS in general.

The main barrier to implementation is cost. Some concerns may be also raised about visual intrusion of new signs. However, by reducing the number of stationary road signs it is suggested that properly designed VMS can reduce negative aesthetic impacts. The costs of VMS are made up of purchase, operating and maintenance. Approximate capital costs are £500.000 for 12 VMS but costs vary significantly depending of type of sign and the appropriate data and sensors required to compute an appropriate message to drivers.

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Text edited at the Institute for Transport Studies, University of Leeds, Leeds LS2 9JT