In large cities with frequent service, it's often only the headway time that is shown when traffic or passenger load would make it difficult to keep exactly to

In large cities with frequent service, it's often only the headway time that is shown when traffic or passenger load would make it difficult to keep exactly to the scheduled times. Example bus stop timetable in London with exact times only given in the early morning and for the last buses of the night: https://twitter.com/se1/status/963786580593905666 https://twitter.com/se1/status/963786580593905666