Those trains in word problems -- who rides them?

    A Problem in a Math Book     by Yehuda Amichai (1924-2000)

     I remember a problem in a math book
     about a train that leaves from place A and another train
     that leaves from place B. When will they meet?
     And no one ever asked what happens when they meet:
     will they stop or pass each other by, or maybe collide?
     And none of the problems was about a man who leaves from place A
     and a woman who leaves from place B. When will they meet,