What is the '14-hour rule' in FMCSA hours of service regulations?

The 14-HOUR RULE is one of the most important and most misunderstood HOS regulations. WHAT IT SAYS: Once a driver begins their duty day (when they go on duty, which may be before the first moment of driving), a 14-hour 'window' opens. The driver may NOT drive after the 14th hour of that window — even if they have remaining time under the 11-hour driving limit. THE CLOCK STARTS: When the driver first goes on duty — this includes pre-trip inspection, loading, waiting at a shipper, any on-duty activity. It is NOT when driving begins. THE CLOCK RUNS: Continuously through the 14-hour period, whether the driver is driving, on duty not driving, or taking non-sleeper-berth off-duty breaks (short breaks during the day). The 14-hour window does NOT extend for non-driving breaks. EXCEPTION — SLEEPER BERTH: The 14-hour window CAN be paused by qualifying sleeper-berth periods of at least 8 consecutive hours, allowing drivers to 'split' their restart. COMMON MISTAKE: A driver who does 2 hours of pre-drive loading, 6 hours of driving, takes a 2-hour rest break, then resumes driving — their 14-hour window has already burned 10 hours (loading + driving + break time); they have only 4 hours of window remaining, even though they've only driven 6 of their 11 allowed hours.