Emergency telephones allow a user or a victim of an accident in a tunnel to contact the control command centre in charge of the tunnel. In addition to establishing a voice link, the use of an emergency telephone by a user also gives their precise location.
Each emergency telephone is given a unique numeral ID which is displayed onscreen when the user/victim picks up the receiver, which allows the control-centre personnel to quickly locate the source of the call. Likewise, the control-command centre can also ring the emergency telephone and provide the user/victim with advisory instructions.
These emergency telephones are installed at fixed intervals on boxes or in emergency stations of different types. The distance between two emergency telephones is often specified by regulations and therefore varies from one country to another.
The structure of this device is quite simple. The emergency telephones in the tunnel are connected to a centre that receives the calls made from the tunnel. Usually, this centre is located in the control-command centre of the tunnel and sometimes in the premises of police services under whose jurisdiction the tunnel is placed.