This is an example of "official" English which summarises the legal consequences of using the emergency brake for an improper reason. Because ultimately a court of law will decide if any "penalty' is appropriate, not the train operator, the word "may" is used. A court may find that misuse has occurred but may choose not to impose a penalty. The language is formal because it paraphrases the terms of legislation which is of course written in a formal style.

misuse just means used improperly. Example: The word was misused and his friend thought he was in trouble, when he wasn't. My kids misuse the kitchen by thinking it is a all you can eat walk through buffet.