What is the ruling on a field employee leaving for his home before the end of working hours, if the remaining time would be spent on his way back to the workplace?

You are required to be present during the official working hours agreed upon in the employment contract. The only exceptions are authorized absences for the benefit of work or to fulfill a need. You must inform your superiors about the situation. If they permit you to go home, then you may; otherwise, you must return to your workplace.