feeling bottleneck situation

I made long-distance routes. The common section is about 3 minutes, and the quarterly section is 6 minutes each. On line B, the train at station 2 does not leave until the train at station 3 leaves, and on line A, the train at station 2 does not leave until the train at station 1 arrives at station 2. What are the problems in general? Order: (stn1->stn2->stn3)