An itinerary is a travel plan. You can say "train itinerary" or "train itineraries" (compound noun rules here), but I can't say that it's the same as "route". "Itinerary" can include several trains which make up a full journey. Good question about the plurals being treated as singular. We do this to mean the plural functions as a single unit, ie. "in total". If you use the plural are/were, then I'd think that each week/pound/litre was separate.

When you're dealing with numbers and measurements even distance, it should be singular.