What is the minimum headway in one direction during single-tracking under river tunnels when the running time is 4.5 minutes?

In the context of train operations, headway refers to the time interval between trains passing a specific point on the track. When operating under conditions such as single-tracking, particularly in river tunnels, the minimum headway is crucial for ensuring safety and efficiency.

Given a running time of 4.5 minutes, it is essential to consider that for trains traveling in opposite directions, the headway must provide enough time for one train to complete its journey through the single-track section before another train begins its journey in the opposite direction. This allows for safe passage and helps avoid head-on collisions.

The correct headway should account for the running time and additional safety buffers. A minimum headway of 10 minutes is appropriate because this allows for the train to travel through the tunnel while also providing a sufficient margin for reaction times, potential delays, and any required operating safety protocols. The 10-minute interval ensures that both train movements can occur safely without compromising operational reliability or safety standards.

Other options presented might not afford the same level of safety or operational efficiency. For instance, options like 5 minutes or 7 minutes are insufficient as they would not provide an adequate buffer considering the running time, leading to a higher risk of operational conflicts. A headway of