VRPTW

The vehicle routing problem with time windows, or VRPTW, is the vehicle routing problem with one rule added: each customer will only take a delivery between certain times. Turn up too early and there is nobody there to receive it; turn up too late and the delivery has failed.

That single addition changes the job considerably. The shortest way round stops being the obvious answer, because the plan now has to get every vehicle to the right place at the right time, not just in the right order. Serving one customer early can mean waiting an hour at the next.

Real operations pile more on top: sites with two or three separate windows, drivers who run out of hours part way through, and journeys that take longer at some times of day than others. Optrak plans against journey times that change through the day rather than one average figure, which is what makes an arrival time it gives a customer one you can stand behind.