Radio COMMUNICATION

A tunnel is an enclosed structure that usually does not permit the natural transmission of radio waves to travel very far into the tunnel.  To ensure that the emergency services and maintenance personnel can remain in radio contact with their colleagues outside the tunnel, it is necessary to install equipment that will provide this service.   

Multiple frequencies can be retransmitted into the tunnel by taking “off-air” radio signals and re-transmitting them into the tunnel to allow:

• Rescue service communication (fire brigade, police...)
• Operator communication (patrols, maintenance crews, taxis, bus companies, ...)
• Public FM broadcasts
• Public DAB broadcasts (Digital Audio Broadcasting)
• Cell phone communication.

There are a very large number of services whose frequencies can be retransmitted into the tunnel.  However, not all of them are retransmitted, due to cost and feasibility issues.  As a general rule, most frequencies used by the rescue services, frequencies used by the operator, a few FM and or DAB frequencies and frequencies of cell phone operators are generally retransmitted.

A radio-retransmission installation in a tunnel essentially comprises of:

• An antenna to receive radio stations “off-air”
• Receivers and transmission units for AM, FM, DAB, Tetra, UHF, that allows broadcasting from the “off-air” outside into the tunnel’s technical rooms
• Voice Break-In equipment to allow emergency messages to be transmitted into the tunnel for FM and DAB frequencies
• Radiating devices in the tunnel (radiating “leaky feeder” cables and antennas).

There is usually no mandatory requirement to provide mobile telephone coverage inside tunnels.  However, since the majority of tunnel users have mobile phones, it is believed to be a safer option to facilitate mobile coverage, encouraging stranded motorists to use their mobiles from inside their vehicles rather than getting out of their vehicles and using the roadside emergency telephones.  Tunnel owners therefore often provide the mobile phone operators with facilities inside the technical rooms to allow them to install equipment that will provide continuing mobile phone coverage inside the tunnel.

See page on Radio break-in systems including Voice Break-In facilities, for further information. 

Smoke control panelS at each portal

The purpose of ventilation in a road tunnel is to provide adequate fresh air and in the event of a fire, to control smoke.

Fresh air is provided through entirely automated systems, based on information from various sensors located throughout the tunnel (opacimeters, CO sensors, NOx sensors…).

For smoke extraction, the nature of the tunnel and in particular its level of surveillance (presence or not of a manned control centre 24/7), will dictate how the ventilation is controlled:

• For tunnels that are monitored by a control centre, smoke control is managed by pre-programmed sequences, triggered by an operator present in the control room.
• For tunnels where the main aim of smoke control is to facilitate emergency service response (fire brigade), manual smoke control systems may be located on site. These systems consist of one or two smoke control panels, located at each tunnel portal.

Each panel can activate smoke extraction, or stop it if required. In certain cases (reversible longitudinal ventilation system), the panels can also control the direction in which the smoke is blown.

If a smoke control panel is located at each portal, it is important to define which panel has priority over the other (for example, when the first panel is activated, it over-rides the second), in order to avoid contradictory commands if fire officers are located at both portals.

Fire mains and hydrant systems

A water supply system, including water mains, fire lines or standpipes, is required to provide water for fire fighting within the tunnel through hydrants (Fig 1) or hose valves (Fig 2) and to possibly provide water for a Fixed Fire Suppression System if installed in the tunnel (see Section 6.3.3 "Water supply" of report 05.05.B 1999). The source of water can be from a water distribution system or from a water tank. The required system pressure must match the requirements of the responding fire brigade.

Hose valves are required within the road tunnel to provide a point of connection for the Fire Brigade to attach fire hoses and gain access to the water supply. Hydrants should be installed at regular intervals within the tunnel (see Section 6.3.3 "Water supply" of report 05.05.B 1999). The hydrant connections must be compatible with the responding local fire brigade(s).