Rail transport crews often need to work on-call, being available to work safely with just a couple of hours' notice at times. The interviewer needs to see that you can comply with the schedule, meeting the needs of Union Pacific Railroad Company and filling the expectations of this role.
If you currently work on an on-call basis, let the interviewer know this. The best way to show your readiness is by explaining that you are already doing it! If you do not have experience being on-call, assure the interviewer that you understand the requirements of this schedule and that you can deliver what is expected of you.