Strategies for Integrating Variable Message Signs in Tunnels and Highways

One of the most important elements within tunnels and highways is communication with the user. For this purpose, variable message signs (VMS) have been used for many years.

Due to the wide variety of devices and manufacturers, it was necessary to define a standard communication protocol to communicate with them, so that any of these devices can be integrated into different systems.

At the national level, the standardized protocol is the DGT protocol (included in the UNE PNE199051-2 Communications Protocol Standard). At the international level, one of the most widely used worldwide is the NTCIP (National Transportation Communications for Intelligent Transportation System Protocol).

Both DGT and NTCIP are a family of standards designed to achieve interoperability and intercommunication between electronic traffic control equipment from different manufacturers and control centers (or equipment).

The important point is that, to have a Smart Tunnel or highway, one of the main integrations is these signs. And not only these signs, but more and more traffic devices, such as traffic lights, for example, are implementing this protocol to communicate. In addition, the ease of sending messages or orders by the tunnel (or road) operator to the device is key. Below, we detail these two key points:

• Firstly, having gateways that implement communication with these protocols is essential. Both DGT and NTCIP are open protocols, therefore, it is possible to implement them in intermediate elements such as RTUs or PLCs, which can be in the field managing communication with traffic devices, while in turn communicating with the control center via standard protocols such as OPC or Modbus TCP. It is also possible to implement these protocols as drivers at the control center or SCADA level, although it is not the most recommended option, since in critical infrastructures such as a tunnel, it must always be ensured that there is local communication between the base control device (such as the PLC) and the final device, so working with concentrator or header PLCs that act as a gateway (and that can also implement control logic) is a good practice.
• Secondly, it is essential that, within the functions of a tunnel control center, there is a message generator and configurator. The message generator should also be designed so that the operator can generate them on their own, without the need for programming or access to the development of the control system.
• As an added factor, the message generator must be integrated within the plan and scenario management tool that every Smart Tunnel should have. From this tool, it should be possible to create sequences that contain steps that send “predefined” messages to the signs.

We leave you in the following video, an example made with the Wonderware platform, where you can see an application for a tunnel control center and the implementation of the message management tool for the signs.