Z: through train
T: Express is two numbers.
K: three digits faster.
N: in-pipe fast
L: temporary inter-office bus
1*** through train that spans more than three innings.
2*** Inter-bureau through train
4***-5*** local train
6*** Inter-bureau ordinary passenger train
7*** Ordinary passenger trains in the pipeline
8*** Railway worker commuter train
Odd numbers mean starting from subordinate offices, and even numbers mean returning to the origin.