Tuna, thank you for your comments and questions- despite your self description of "not knowing much about trains", you make astute observations that seemingly few make. As for the building of passing tracks to allow locals to wait for expresses to pass, this is what is called a "timed overtake", which I believe in North America is quite rare, at least outside the NYC MTA, though commonplace in some parts of Europe (Switzerland) and very common in Japan. It requires a modern traffic control system with PTC, as well as timetabling with all trains running to schedule- in Japan trains are timetabled down to 15 seconds, even less in some urban networks. In the North American context, this is next to impossible, with enormous freight trains with massive stopping distances as well as testudinal acceleration. Even with passenger only lines, loco hauled trains are a drag on operating a viable timed overtake, with their slower acceleration vs. multiple units.