Which of the following factors is most likely to lead to a secondary delay in train operations?

Secondary delays in train operations often occur as a chain reaction due to initial delays or disruptions. In this context, overloading of the following train plays a significant role. When a train is overloaded, it can lead to slower acceleration and reduced efficiency in operation. This impacts its schedule, as it might not be able to maintain the expected intervals and speed on the track. Consequently, if one train falls behind due to overloading, it can affect the trains behind it, leading to a cumulative effect of delays throughout the system.

In contrast, while speed limits, unscheduled maintenance, and passenger boarding times can lead to delays, they are typically more contained and do not inherently cause a ripple effect. Speed limits are designed to ensure safety and, although they may slow down a train, they usually do not directly result in subsequent trains being delayed. Unscheduled maintenance can certainly cause a delay; however, it is usually an isolated incident rather than something that triggers further delays downstream. Passenger boarding times are primarily related to the operations of a single train and are often managed effectively through scheduling and boarding procedures, minimizing their impact on following train schedules.

Therefore, the overloading of a following train stands out as a factor that inherently disrupts the sequential flow of train operations