When you answer this question, avoid merely listing off the equipment that you have used. Make your answer more conversational by also discussing any training you have received, troubleshooting you have done, and any areas of expertise you may have.
If you have no experience working around or operating heavy equipment, that is okay! Union Pacific Railroad Company is willing to train the right person. Be sure to express your eagerness to learn. You could offer to take some coursework or training before your hire date, which will strengthen your knowledge before you start your new job.