Next year, in March, several bus routes may be restructured to serve UW Station and Capitol Hill Station, with more frequent all-day service. It is nice to know that there will be another bus for your route coming every 15 minutes. But for riders transferring from Link trains arriving every 10 minutes off-peak, 15-minute frequency may create problems.
With such a service pattern, every other bus may be crowded, and every other bus relatively empty. On long routes (like route 372), the emptier bus may slowly but surely catch up with the full bus, leading to a pattern where two buses pull up back-to-back, every half hour, at the other terminus. This commonplace phenomenon is known as “bus bunching“.
It may make more sense for minimizing wait time at stations, stabilizing headway, and enabling operators to get their scheduled rest breaks, to keep these routes on either 10-minute-headway or 20-minute-headway, depending on ridership demand for that time of day.
Practical reliability may trump theoretical legibility.