I am not clear why the Muni drivers' contract called for a bonus rather than a higher hourly rate. Because it is based on having been paid for at least x number of hours of work in the year, I wonder if it was done to discourage unplanned missed days without pay which would make it difficult for the Muni to have enough vehicles on the street. Whatever the reason, it is only a way of structuring compensation. Whether the drivers are paid too much (or too little) is another question.