How drive time and ETA are calculated
Moving time equals distance divided by average moving speed. Planned break minutes are added to get total elapsed trip time. When a valid departure clock time is entered, the elapsed time is added to produce an estimated arrival clock time and any next-day offset.
Use a realistic average moving speed
Average moving speed is not the speed limit or the fastest speed reached. It should reflect slower roads, traffic, weather, construction, and the route mix. Breaks, refueling, meals, and planned stops belong in the separate break-time field.