Highways Agency

• Variable Message Signs (Electronic Message Signs)

Frequently Asked Questions - Variable Message Signs (VMS)

The primary purpose of electronic message signs (more commonly known as Variable Message signs or VMS) on the Agency’s network is to communicate information and advice to drivers about:

• Emergencies e.g Major or National Emergencies
• Incidents e.g accidents and lane closures
• Network Management e.g Roadworks.

Here we have provided the answers to some frequently asked questions regarding the electronic message signs located on our network:

• Q1 What is a variable message sign?
• Q2 Who is responsible for variable message signs?
• Q3 How many variable message signs are there?
• Q4 What do VMS look like?
• Q5 Why do we have variable message signs?
• Q6 Who puts the information  on variable message signs?
• Q7 How do they work?
• Q8 How long does information stay on the VMS?
• Q9 What happens if the information on VMS is wrong?
• Q10 Why does a sign still display 40 even though traffic is at a standstill?
• Q11 Why do you display signs such as ‘watch your speed’ and ‘ think, don’t drink and drive’?

Q1 What is a variable message sign?

Electronic variable message signs (VMS) are signs that are located at key decision  points on the motorway and trunk road network. They display advice to drivers about emergencies and incidents to improve safety and minimise the impact of congestion.

Q2 Who is responsible for variable message signs?

The Highways Agency are responsible for all of the signs on the Highways Agency network. This is managed through the 7 Regional Control Centres based around the UK and a National Traffic Control Centre based in Birmingham.

Q3 How many variable message signs are there?

We have around 2,200 VMS on our network. Of these 459 are located at key decision points around the network i.e. before major junctions such as the M5/M6 Link. In addition to these there are a further 1,887 local safety VMS.

Q4 What do VMS look like?

Below are examples of signals and signs, which are all types of VMS, in use on the Highways Agency network;

• Central Reserve Post Mounted Signals - also known as matrix signals. These signs can cater for up to three lane motorways and major trunk roads. They are spaced at 3km intervals and they are limited to display advisory fog warnings, speed restrictions and lane closures with flashing amber warning lanterns.

• Slip Road Mounted Signals - These are normally situated in pairs at entry slip roads. Like the signs above they are used to display advisory fog warnings, speed restrictions and lane closures with amber flashing lanterns. An additional feature of this signs is to display red lanterns to allow closures of slip roads only.

• Gantry Mounted Signs - These signs allow for flexibility for individual lane signalling. These signs can also display fog warnings, speed restrictions, lane closures and lane diversions. It can also display a red ‘X’ and red flashing lanterns to provide a mandatory stop signal. These signs are spaced at 1km intervals.

• Enhanced Message Signs - These signs can be mounted on either cantilever posts or alongside Gantry Mounted Signs. They display information about incidents or hazards. The legends inform motorists of the reason why the signals have been set.

• Message Sign Mark 3 (MS3) - These signs are mounted on cantilever posts and they display information about incidents, hazards and campaign messages.

Q5 Why do we have variable message signs?

Those VMS located at key decision points are to advise drivers about ‘major’ incidents and diversion routes where there is a suitable alternative available. The local safety VMS are mainly located on motorways to provide information to motorists about local traffic conditions ahead of them in the event of an incident. For example they provide advance warnings of slow or stationary traffic. 

Q6 Who puts the information  on variable message signs?

The message you see on the Variable Message Signs can be set automatically, by a system called MIDAS, which stands for Motorway Incident Detection and Automatic Signalling system, or manually by our control room staff. Around 3.9 million messages were set on VMS in 2006.

Q7 How do they work?

All motorways and major trunk roads are covered by one of our seven regional control centres. Operators at the regional control centres liaise with police in regards to incidents and events on our network. The police notify the Regional Control Centres (RCCs) so that they can set local signs to warn drivers in the vicinity of the incident. The RCC then notify the National Traffic Control Centre, based in Birmingham, so that if there needs to be signs set further away, if the incident is expected to last a long time, motorists further away can also be informed. The NTCC are also alerted to events and set signs based on alerts from their system as well as information from the RCC’s and local Police forces. The NTCC has the option of signing a diversion route if there is a suitable plan or alternative available. 

The Regional Control Centres also monitor the MIDAS system. MIDAS stands for Motorway Incident Detection and Automatic Signalling. MIDAS detects incidents or congestion from loops in the road and automatically sets overhead signs with messages such as ‘QUEUE- CAUTION’ or ‘QUEUE AHEAD’ to warn drivers of conditions of the road ahead, together with the maximum speed advised. The signal settings are switched off automatically a short time after traffic returns to free flow conditions. MIDAS can be overwritten manually by operators but only in extreme circumstances.

• M25 Controlled Motorway

The original section of the controlled motorway in place between the M3 and M4 (junctions 12 to 15) had four lanes running in each direction and three lanes through each junction. Traffic demand on the M25 typically increases by 2% each year and we need to manage the demand effectively. As the traffic demand increases, inevitably we must expect the signals to be set.

There are two signal settings for the controlled motorway section. These are;

• Signals set for congestion - These are set in response to the number of vehicles per minute passing over traffic detectors. As demand increases so does the risk of flow breakdown and accidents. The signals are set to reduce the speed of the traffic, smooth the flow, reduce the potential for flow breakdown and create a safer environment for the current traffic conditions. Initially 60 mph signals are displayed on the gantries and then as the traffic demand increases further, 50 mph signals are displayed.

• Signals set for incidents - These are set when the system detects very slow moving or stationary traffic. The signals provide warnings to protect queuing traffic and provide a safer driving environment. When a queue is detected, the system rapidly sets signals to 40 mph in the immediate area to protect queuing traffic and 60 mph signs leading into this, giving advance warning to drivers alerting them to reduce their speed.

The signal system is intelligent and prevents the signals changing the limits displayed or switching the signals ‘on’ and ‘off’ too quickly. This gives drivers time to respond and ensure the signals are not confusing. Once the signals are switched on, timing delays are introduced to stop signals switching off prematurely.

• M42 Active Traffic Management Section

The M42 between junctions 3a and 7 is part of the Active Traffic Management system. The main purpose of active traffic management is to manage congestion, but it can also be used to manage the traffic around an incident, should one occur. There are 3 different operating states of the active traffic management section which are detailed below.

• Normal Motorway Conditions - In this operating state there is no congestion, therefore no signs are set and national speed limit applies. The hard shoulder is not in use and the emergency refuge areas are to be used in the event of a breakdown.

• Active Traffic Management without hard shoulder running - In this state the signs indicate congestion or an incident ahead and reduced speed limits which must be obeyed. There is a red cross over the hard shoulder meaning that this lane must not be used unless in an emergency. The system sets the same speed across the carriageway which reduces the need for drivers to change lanes. Where necessary the system also sets messages on the driver information signs to inform road users of the road conditions ahead of them.

• Active Traffic Management with hard shoulder running - In this operating state the signs show that there is an incident or congestion ahead. There are speed signals set and these must be obeyed. The information boards on the gantry provide drivers with information. The hard shoulder could be used within the junctions in this operating state to ease the possible build up of traffic. The hard shoulder will only be used once the Regional Control Centre operators have checked that it is clear of debris and vehicles.

Q8 How long does information stay on the VMS?

Signs are set to advise of incidents or emergencies stay set until the incident has cleared. Signs set automatically remain set until the traffic sensors detect that the traffic flow has returned to normal.

Q9 What happens if the information on VMS is wrong?

It is the case that because of the time lag between an incident occurring, the information being passed by the public to the police and the equipment being set, there will inevitable be instances when a number of motorists will either have no warning of the incident, or settings remain in place  after the scene is clear, whilst the control room is being updated. The Highways Agency is aware of the problems with our current signing system  where sometimes the signs are displaying the wrong message, which can be misleading or at times, say nothing at all. The Agency is taking active steps to ensure that the incidence of this is reduced in the future.

Q10 Why does a sign still display 40 even though traffic is at a standstill?

At present when a message is displayed to warn of a queue ahead the automatic system also displays the lowest advisory speed limit to be set at which is 40mph. As these signs are automatic, they cannot be switched off until the traffic has cleared.

Q11 Why do you display signs such as ‘watch your speed’ and ‘ think, don’t drink and drive’?

These messages are Safety campaign messages, aimed at improving general driver behaviour. They support other national safety campaigns such as the Department for Transport campaign. These signs would be overwritten in the event of an incident.