In a road tunnel, the equipment plays a vital role for the safety users. The operator therefore has to monitor such equipment continuously for determining their status (working or fault) and/or their operating mode (automatic, manual or stopped).
Many devices are servo-controlled by sensors and operate automatically (lighting, ventilation...) according to pre-determined thresholds. Others are activated or deactivated depending on the operating conditions. It is thus useful for the operator to be able to remote control them (signalling, variable message signs, barriers, ventilation, lighting, pumps ...).
Lastly, since the equipment may be operated very differently (continuous, occasional, or very rare), it is necessary for the operator to have information on the operational duration (hour used) for each of them.
These functions of surveillance, control-command and data archiving are very often performed by a single system: the Supervisory Control And Data Acquisition system (SCADA).
Several SCADA systems are available worldwide and their performance is being improved constantly. The systems installed in road tunnels of comparable characteristics are therefore rarely completely identical, even for the tunnels of the same operator. Even so, the architectures follow certain rules that are widely prevalent: