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In reality, trucks do not respect the TUM in an instant in time - in any one instant, the truck is either available or unavailable, not a mixture of the two. There’s a probability of whether a truck will be operating at an instant in time in the future (the TUM is the average over an extended period of time). This is the most correct way to think about trucks on an instantaneous basis, and for very short term scheduling. The TUM accounts for but does not explicitly contain, the frequency and duration of downtime events (a cyclone vs a broken bucket tooth).
Version 21.1 of APS now supports both methods to accommodate either paradigm.
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