A ventilation system for road tunnels, which comprises at least one fan and a power supply and actuation apparatus which is connected to an electric power supply line and supplies electric power to the fan ; wherein said power supply and actuation apparatus comprises an electronic control system configured to control the speed and the direction of rotation of the fan and comprises an electrical conversion device interposed between the power supply line and the fan ; wherein the system further comprises at least one temperature detection device, and wherein said power supply and actuation apparatus comprises a motorized switching unit which is configured to modify, as a function of the temperature detected by said temperature detection device, the configuration of said power supply and actuation apparatus : from an ordinary configuration, in which said power supply and actuation apparatus supplies power to the fan by means of said electrical conversion device , to an emergency configuration, in which said motorized switching unit isolates said electrical conversion device , creating an electrical bypass so as to supply power directly to the fan from said electrical line , and from an emergency configuration to an ordinary configuration, characterized in that said power supply and actuation apparatus comprises also a thermostat which is configured to actuate said motorized switching unit in order to provide said emergency configuration when the thermostat detected temperature is equal to or greater than a predetermined threshold temperature. wherein said power supply and actuation apparatus comprises an electronic control system configured to control the speed and the direction of rotation of the fan and comprises an electrical conversion device interposed between the power supply line and the fan ; wherein the system further comprises at least one temperature detection device, and wherein said power supply and actuation apparatus comprises a motorized switching unit which is configured to modify, as a function of the temperature detected by said temperature detection device, the configuration of said power supply and actuation apparatus : from an ordinary configuration, in which said power supply and actuation apparatus supplies power to the fan by means of said electrical conversion device , to an emergency configuration, in which said motorized switching unit isolates said electrical conversion device , creating an electrical bypass so as to supply power directly to the fan from said electrical line , and from an emergency configuration to an ordinary configuration, characterized in that said power supply and actuation apparatus comprises also a thermostat which is configured to actuate said motorized switching unit in order to provide said emergency configuration when the thermostat detected temperature is equal to or greater than a predetermined threshold temperature. from an ordinary configuration, in which said power supply and actuation apparatus supplies power to the fan by means of said electrical conversion device , to an emergency configuration, in which said motorized switching unit isolates said electrical conversion device , creating an electrical bypass so as to supply power directly to the fan from said electrical line , and from an emergency configuration to an ordinary configuration, characterized in that said power supply and actuation apparatus comprises also a thermostat which is configured to actuate said motorized switching unit in order to provide said emergency configuration when the thermostat detected temperature is equal to or greater than a predetermined threshold temperature. <EOS>