On-duty time is all time from when a driver begins work, or is required to be in readiness to work, until the driver is relieved from work AND from all responsibility for performing work. That definition, from § 395.2, is the one every hours-of-service limit is measured against — so before any number in this chapter means anything, it has to be clear what the clock is counting. Driving time, by contrast, is narrow: all time spent at the driving controls of a commercial motor vehicle as § 390.5T defines it in operation. Driving time is always on-duty time; on-duty time is very often not driving.

§ 395.2 then removes the guesswork by listing what on-duty time includes. All time at a carrier’s or shipper’s property, or on any public property, waiting to be dispatched — unless the driver has been relieved from duty by the carrier. All time inspecting, servicing or conditioning any commercial motor vehicle, at any time. All driving time. All time loading or unloading, supervising or assisting with it, attending a vehicle being loaded or unloaded, remaining in readiness to operate, or giving or receiving receipts for shipments. All time repairing, obtaining assistance for, or remaining in attendance upon a disabled vehicle. All time providing a breath sample or urine specimen — including travel time to and from the collection site — for Part 382 testing when directed by a carrier. Any other work in the capacity, employ or service of a motor carrier. And any compensated work for a person who is not a motor carrier at all.

The exclusions are shorter and just as consequential. Time in or on a commercial motor vehicle is on duty EXCEPT time spent resting in or on a parked vehicle; time spent resting in a sleeper berth; and up to 3 hours riding in the passenger seat of a property-carrying vehicle moving on the highway, immediately before or after a period of at least 7 consecutive hours in the sleeper berth. That third exclusion looks like a technicality and is not — it is the hinge the split sleeper berth turns on, and § 7.4 uses it directly. Read the list as a whole and the design is clear: waiting is work, paperwork is work, a second job is work, and only genuine rest stops the clock.