I'm facinated at the various interpretations of the lyrics. I do want to point out that feildmaster is right that it should be "Happiness hit her like a train on a track". Now relisten to the song and you will notice that the music is definately mimicing a train and her Wohoohoo is even mimicing the whistle. The music builds as the train would go faster. Its a facinating piece of music. I'd like to think its more about someone resisting falling in love and is mearly run down by it. But I think the interpretations about it being about an abusive love are worth considering.