The FM and DAB+ break-in system in tunnels
In road and highway tunnels, regular radio programming can be interrupted at any moment to broadcast urgent messages to all vehicles in transit. This function — the VBI (Voice Break-In) system — turns the tunnel's FM/DAB+ infrastructure into a direct emergency communication channel.
What the VBI system is
The VBI overrides normal FM and DAB+ transmissions with priority messages broadcast from inside the tunnel. When a driver travels through the tunnel tuned to their preferred station, the system can interrupt programming — automatically or through a manual operator intervention — and broadcast urgent communications to all vehicles simultaneously.
In an enclosed environment where visibility is limited and escape routes are fixed, reaching all users instantly can be the difference between an orderly emergency response and a chaotic situation.
Break-in system applications
Emergency management
In the event of a fire, the system immediately transmits evacuation instructions — nearest emergency exits, procedures to follow. During an accident, messages guide drivers on where to stop and how to facilitate access for emergency vehicles.
Traffic and safety information
Beyond emergencies, the VBI communicates alerts about sudden queues at the tunnel exit, reports of stationary vehicles or ongoing roadworks, and adverse weather conditions beyond the tunnel portal.
Service communications
The system can also carry scheduled information: section closures for maintenance, mandatory diversions for road works.
The break-in system's technical infrastructure
Amplifiers
The core of the system is the intelligent amplifiers positioned along the tunnel. They receive the FM and DAB+ signal from external Yagi antennas, amplify it, and integrate the modules for inserting the break-in message across all active carriers.
Activation modes
The system activates through multiple channels:
- Automatic activation via API interfaces or SNMP protocols, integrated with tunnel monitoring systems — smoke sensors, incident detectors, video surveillance systems.
- Manual intervention by the control center operator, via a SIP VoIP call directly to the system: the operator's voice is transmitted in real time across all active FM frequencies and DAB+ multiplexes.
Text messages and images
Modern systems also support text messages that appear on the infotainment display of compatible vehicles. On DAB+, it is possible to send images — universally recognizable emergency symbols — that appear automatically on displays, overcoming language barriers.
Radio channel selection and management
FM carriers
The amplifiers allow precise selection of which FM stations to amplify inside the tunnel, based on the geographic area and local listening habits. The goal is to ensure that most drivers can receive the emergency message on the station they are already tuned to.
DAB+ ensembles
The system also selects which DAB+ multiplexes to rebroadcast in the tunnel. Each ensemble can contain multiple stations and data services; the selection considers coverage of the main national and local broadcasters to ensure continuity of the most important information services.
Regulations
European Directive 2004/54/EC sets the minimum safety requirements for tunnels on the European road network. The obligation to install emergency communication systems with break-in capability applies to tunnels longer than 1,000 m with traffic exceeding 2,000 vehicles per lane. In these tunnels, the regulation requires a broadcasting system capable of interrupting radio programming to broadcast safety messages from the control center.
Legislative Decree 264/2006 transposes the directive in Italy. The Ministerial Decree of 12/07/2021 reinforced the obligations for scheduled maintenance and monitoring of safety systems, including broadcasting systems. Operators may install retransmission and break-in systems in tunnels shorter than 1,000 m when a risk assessment or traffic conditions require it.
ETSI has produced specific technical standards: ETSI TS 102 182 describes the integration of the VBI function in tunnel broadcasting systems; for DAB+, standard EN 300 401 defines the "Alarm Announcement" function. Minimum audio quality levels, maximum activation times, and periodic testing protocols are defined by the concessionaires' technical specifications and ANAS standards.
Maintenance and reliability
A VBI system must always be ready to operate. Periodic tests go beyond technical verification: the messages must be clear and intelligible under real operating conditions. Reliability is achieved through component redundancy — if one element fails, the others keep the service active.
Frequently asked questions
How does break-in interrupt the vehicle's radio?
The VBI message is radiated inside the tunnel at a power level sufficient to override the ordinary station signal. The vehicle's radio receives the new signal on the same FM frequency or DAB+ multiplex it is already tuned to.
Does the system work on vehicles with modern navigation or infotainment?
Yes. For FM, the VBI acts on the standard audio signal. For DAB+, modern systems also transmit text messages and images that appear directly on compatible vehicle displays, supplementing the voice communication.
Who can activate break-in and how quickly?
Activation occurs in two ways: automatically, via tunnel sensors integrated through API or SNMP; manually, by the control center operator via a SIP VoIP call to the system. In both cases activation is immediate.
From what tunnel length is it mandatory?
Directive 2004/54/EC (Legislative Decree 264/2006) requires emergency communication systems with break-in capability in trans-European network tunnels longer than 1,000 m with traffic exceeding 2,000 vehicles per lane. Shorter tunnels may still include the system as required by the operator or competent authorities.