Working in conjunction with EI-WHS, Ematics have been awarded the contract for the provision of a replacement Variable Message Signing System (VMSS) for the Butetown Link Tunnel in Cardiff.

The project implementation is over 2 phases spanning 2 years. Phase 1 comprises the design of the full replacement VMSS System and implementation of the new top end system. Phase 2 comprises the installation and commissioning of replacement bottom end sign drivers.
The Tunnel is approximately 700m long, has two bores which feed the Cardiff Bay area. The Tunnel is operated by Cardiff Council via the Urban Traffic Control system, located at County Hall in Cardiff.

The VMSS system implements sign plans, which request the setting of individual signs within the tunnel and on the tunnel approaches. The selection of sign plans is based on actual road conditions in terms of traffic flow, incidents and maintenance activities etc. Overall, the system controls 40 lane control signs within the tunnel, 8 portal mounted VMS signs and 4 gantry mounted VMS signs and 2 post mounted VMS signs on the tunnel approaches.

The Top end SCADA system is in dual redundant configuration, running under Windows 2003 operating system on High Availability PC Servers. The system provides operator interface functionality at the Tunnel Services Building and at the traffic operations room in County Hall. The SCADA system also interfaces with a Siemens UTC system for receiving traffic plan requests and for reporting status of the various signs within the scheme. The SCADA system also hosts a Microsoft SQL Server Database which contains all the required sign plans. This database is configurable via a user-friendly graphical user interface (GUI) for modification/creation of sign plans by the end user.

At lower level, Ematics have developed a PLC based system to interface with the gantry, portal and post mounted VMS signs. This PLC is effectively a straight replacement for the existing NMCS2 Transponder. It communicates with the signs using standard Highways Agency 5 byte NMCS2 messages via existing RS485 cables. It also provides an Ethernet interface and communicates with the top end system via Modbus TCP protocol. This PLC has been developed to be user configurable such that additional signs can be added in the future if required (PLC will accommodate up to 30 signs).

Overall, the use of modular design principles and off-the-shelf components leads to a more cost effective system, with the end user not locked in to a specific vendor company. This presents the end-user with future benefits in terms of system maintainability and upgradeability.

The Tunnel Lane Control Signs are controlled via a digital interface to PLC's.
The VMS Signs are controlled via standard Highways Agency 5 byte NMCS2 Protocol.

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