The whole verify-your-passport thing is confusing, and I'm still not sure exactly when it's required. But be aware that with everybody buying online or via machines, open ticket counters are few and waits can be long.

Also confusing are those gate scanners. Sometimes they work with a passport. Sometimes you're just hustled to the manual gate. Remember there's also a gate when you exit at the end of your trip.

(And etickets aren't limited to D and G trains. Most trains now use them.)