A driver who has been on duty too long is not a scheduling inconvenience — it is the single most preventable cause of a bus accident.
FMCSA hours-of-service rules for passenger-carrying commercial drivers set hard limits: a driver cannot drive more than 10 hours following 8 consecutive hours off duty, and cannot drive at all after being on duty 15 hours following that same rest period. Weekly limits cap drivers at 60 hours on duty in 7 consecutive days for carriers that do not operate every day, or 70 hours in 8 consecutive days for carriers that do.
These limits are tracked through Electronic Logging Devices on most commercial passenger vehicles, and carriers are required to retain driver time records for a minimum of six months, available for inspection within two business days of a request. A trip that requires more driving than a single driver can legally provide — a long overnight run, for example — needs a second, relief driver, not a driver pushing past the legal limit to make up time.