I am looking for theoretical results on mTSP (multiple travelling salesmen problem) over structured/modular graphs. If the meaning of "modular" is not clear, think about a graph that represents a building where all floors are exactly the same. The whole building is the graph, every floor is a "module" of the graph. This means that the graph is highly structured and probably there can be some efficient approximated algorithms.
The specific result I am looking for is about what you can do when you have number of salesman persons = number of modules, but for the moment it'd be perfect to have any kind of result.
Actually I searched a lot but I couldn't find anything on this topic. Maybe I don't have enough searching skills.