Many work at night or on weekends, because most large post offices process mail around the clock, and the largest volume of mail is sorted during the evening and night shifts. Workers can experience stress, as they process ever-larger quantities of mail under tight production deadlines and quotas. Overtime hours are frequently required for urban carriers during peak delivery times, such as before the winter holidays. A carrier's schedule has its advantages, however. Carriers who begin work early in the morning are through by early afternoon and spend most of the day on their own, relatively free from direct supervision.
Carriers spend most of their time outdoors, delivering mail in all kinds of weather.
Even those who drive often must walk periodically when making deliveries and must lift heavy sacks of parcel post items when loading their vehicles. In addition, carriers must be cautious of potential hazards on their routes. Wet and icy roads and sidewalks can be treacherous, and each year numerous carriers are attacked by dogs. The U.S. Postal Service employed 299,000 clerks and 332,000 mail carriers in 1998. About 95 percent of them worked full time.