I was asked if Sankey diagrams could meaningfully be used to visualize passenger loads on a tram or bus line. Here is what I came up with:

These are fictitious values. I just labeled the stops A, B, C, … and decided to go for a short feeder line. At the last stop all passengers get off (e.g. to transfer to a train).

At each stop there are passengers that get on (green) and get off (red). The number of pax on the bus is shown by the blue arrows.

The profile would probably look differently at different times of day, so depending on the data availability one would have to create diagrams for off-peak/peak hours, weekdays/holidays and so on.

Your thoughts?