Highways Agency - Safe roads, Reliable journeys, Informed travellers

Displaying Travel and Delay Times on Variable Message Signs - Frequently Asked Questions

Related pages

• Variable Message Signs (Electronic Message Signs)
• Travel and Delay Times on Variable Message Signs - Introduction

Why are we providing these signs?

The Highways Agency's main aim is safe roads, reliable journeys and informed travellers.  One way in which we are contributing towards this is by providing accurate real-time journey information to drivers. 

We already have variable message signs on our road network and we regularly collect real-time data on traffic flows to update our website and the media. We are making the best use of these resources by combining them to give motorists up-to-date travel and delay time estimates whilst they are on the road.

The information currently displayed on variable message signs is indicative in nature rather than quantitative. By showing travel and delay time estimates on the signs, it gives you a clearer indication of what the road ahead is like and helps you to make an informed decision about your journey.

How does it work?

Data is recorded by automatic number plate recognition cameras (ANPRs) positioned next to the motorway. From this data, we have built profiles of the length of time it normally takes to get from one point to another on the motorway network. Using these profiles, and the latest data from the cameras, we are able to estimate the time it will currently take to complete a journey between two points. The signs are automatically updated every five minutes so that they take into account the current traffic conditions.

The data we collect from the ANPR cameras is scrambled at the point of collection so that at no stage do we have access to any details on individual vehicles.

Why are there travel and delay messages?

If something causes a delay on the road network (such as an incident or roadworks) above a pre-determined threshold, the signs automatically change from displaying travel times to showing delay times.

Delay times are estimated by an operator at the National Traffic Control Centre who has regard to a range of factors including the type of incident causing the delay, the time of day, the weather and the volume of traffic likely to be affected.

Example messages:

Travel Time Message

Delay Time Message

What signs are being used?

The size of individual signs determines how the travel and delay time information is displayed. For example, on signs that are two characters high by 12 characters across, we will just provide the travel or delay time to a destination.  For bigger signs, that are three characters high by 18 characters across, we can provide the travel or delay time and the distance to the destination. Customer feedback on the trial indicated that this distance information was useful to help drivers understand the travel and delay times.

Larger signs (3x18 characters)

Smaller signs (2 x 12 characters)

Why don't you give the time it will take to get into to the town/city rather than to a junction number?

Our research has shown that drivers will often use different routes to get into town or city centre once they have left the motorway. It is for this reason, as well as the fact that we only collect data on those roads for which we are responsible, that we cannot give accurate estimations for individual destinations off the motorway network.

We appreciate that drivers may not know the locations of individual junction numbers but are usually aware of the junction that they will be leaving the motorway. In order to make the signs as informative as possible, our larger variable message signs show both the junction number and the primary destination from that junction, with the travel or delay time information.

How accurate are the times?

The times are constantly monitored by our National Traffic Control Centre and take into account events, such as road works or incidents, to try and ensure that the times displayed are as accurate as possible. We liaise closely with strategic traffic generators, such as football grounds and concert arenas, so that we are aware of any events that could increase the volume of traffic on the motorways.  The dynamic nature of road traffic means accuracy will not always be achievable.

What speed are the times calculated on?

The times are not calculated using distance and mph, but are actually based upon a typical traffic profile of an individual stretch of motorway. This means that during peak times the travel time messages give an accurate reflection of traffic flow.

Travel times are capped to reflect legal speed limits.  Drivers should always adhere to road speed limits and also have regard to advisory speeds on variable and fixed signs to ensure that they are driving in a safe and legal manner.  

How are these signs used with other VMS?

The travel and delay time signs are used in conjunction with other signs.  They are a lower priority than safety and incident signs and strategic travel information, so they will be over-written if this sort of information needs to be displayed.