What action should a driver take if their vehicle breaks down in a tunnel?

When a vehicle breaks down in a tunnel, the most appropriate action for a driver to take is to use the emergency telephone to call for help. This is crucial because tunnels often have specific safety protocols in place to manage emergencies, and using the emergency phone ensures that help is dispatched in a safe and controlled manner.

Emergency telephones are typically located at regular intervals along the tunnel and are connected directly to the tunnel control center. By using these phones, drivers can provide their exact location and details of the situation, allowing for a swift and effective response by rescue services.

In the context of the other options, flagging down a passing vehicle may not be safe or practical due to the confined space of a tunnel and the potential for other vehicles to be approaching quickly. Pushing the car out of the tunnel could put the driver and passengers at risk, especially if they are not completely aware of the traffic conditions behind them. Lastly, using a flare to signal for help can be dangerous in an enclosed space like a tunnel, as it poses fire hazards and can also create panic or distraction among other drivers. Therefore, using the emergency telephone is the safest and most effective course of action in this scenario.