Why is it when a bus on the stopwatch says 3 or 6 min until it's due, and once that bus comes within 2 min, it leaves without waiting for those last few minutes? It confuses many and I have missed buses this way.
This is a common confusion (and frustration) for riders. There are two primary points to keep in mind.
First, are you boarding at a timepoint or a stop in between? Timepoints are listed at the top of every route's schedule and are times that drivers must adhere to. If the bus is running ahead of schedule, the operator must wait until the scheduled time before they can depart a timepoint. If the bus is running behind schedule, the timepoints help dispatchers decide if that bus should be "turned" to help restore on-time service.
If you are not boarding at a timepoint, any times given by the Trip Planner are estimates. When STOPwatch reports that a bus will depart your stop in six minutes that estimate is based on the current location of the bus and an algorithm. This algorithm calculates a departure time for your stop based on the specifics of the corridors the bus is traveling along. The realities of sharing the road with other vehicles, stop lights, traffic, heavy passenger loads, passengers fumbling for ID/fare, etc. cannot be accounted for in the algorithm. Situations like the benevolence of other vehicles to let a bus back into traffic or a backed up four-way stop, are just a couple of the challenges faced. This is likely why you'll see the disparity you're describing above.
Second, there are things you as a rider can do to improve your experience. Buses send out data every 30-seconds. If you receive information that the bus will arrive in six minutes, send another request two minutes later to get an update. If your bus hits a series of green lights, the departure time will likely change.
The word "departure" is a well chosen description. STOPwatch gives you the time the bus will depart a stop, not arrive. We encourage all passengers to arrive at their stop five minutes before the departure time. If MTD operated along a railroad track, service delivery would be different. But the unpredictability of the shared road make it imperative to be at your stop five minutes before.
This isn't the first time we've heard these concerns. We think a re-education or a new layer of marketing is in order. Any thoughts or suggestions?