Final answer:
The minimum headway for single-tracking operation exceeds the run time of 3(1/2) minutes between towers due to necessary time additions for safety, boarding, and traffic intervals.
Step-by-step explanation:
The question of determining the minimum headway in one direction when operating single-tracking involves calculating the shortest time interval necessary between two trains using the same track so as to avoid collisions.
Given that the running time between two towers is 3(1/2) minutes, we must also account for additional factors such as the acceleration and deceleration time, the time needed for passengers to board and alight, and any safety measures. Without specific values for these variables, a precise calculation cannot be provided. However, the minimum headway would certainly be longer than the running time itself to ensure safe operation.