Principles of the travel scheduling problem

Comment:

Underlying principles of the travel scheduling problem?

Follow-up:

Frankly speaking we also do not know the complete picture of this problem. Yet from an intuitive angle, the problem enlarges the complexity of the original shortest path problem in at least two dimensions. Firstly, we need to solve multiple instances of the shortest path problem for any single round-trip tour (e.g., one day in the trip). Secondly, we need to combine these shortest path solutions temporally across different tours so as to obtain the minimum overall cost for the whole trip.