Tamar Bridge Tidal Flow System

Around ten thousand cars cross the Tamar bridge and pass through the single bore Saltash tunnel on the A38 every day, with the vast majority of vehicles heading east into Plymouth in the morning, and west out of the city in the evening. To reduce congestion at these peak times, SSL’s Tidal Flow System allows two of the three lanes to be used for the prevailing traffic conditions.

The Tidal Flow System (TFS) and SCADA software is a complex mixture of various elements such as Lane ControlSigns, Lane Segregation Signs (Bus and Car lanes), Illuminated Road Studs, Diversionary road signs (Variable Message Signs or VMS), text message signs (EMS), and environmental monitors: pollution levels, fan control, emergency phone door detection, sump control, lighting control, monitoring of doors, switchgear, intruder alarms, and the Inergen (fire suppression system) and UPS systems.

The user interface was designed to be easy to operate by mimicking lane controls and message signs, and giving clear and unambiguous information about the environment (SCADA).

There are 29 lane control plans, and the software manages the complex task of setting each of the signs to ensure there are no conflicts between east bound and west bound settings. Before opening a lane to new traffic, the software will pose questions to the operator, to ensure that it is safe to continue.

Multiple EMS can be set with a diversion plan, it is also possible to set these messages on a sign-by-sign basis if required. This was a "ground up" development fully operational within 24 weeks of contract award. Subsequently, SSL have undertaken upgrades to the system software to accommodate new equipment added, including Wide Area Diversion VMS, and a host of additional Tunnel Safety Functions, including Lane Studs and Wigwags. SSL maintain this system as part of their Highways Agency Software Maintenance Contract.