Clock-face scheduling

A clock-face schedule or cyclic schedule is a timetable system under which public transport services run at consistent intervals, as opposed to a timetable that is purely driven by demand and has irregular headways. The name derives from the fact that departures take place at the same time or times during the day. For example, services with a half-hourly frequency might leave at 5:15, 5:45, 6:15, 6:45, 7:15, 7:45 etc.

The goal is to enhance the attractiveness and versatility of public transport. Clock-face schedules are easy for passengers to memorise because departure and arrival times occur at consistent intervals, repeating during the day. A regular repeating schedule over the whole day can also improve services during off-peak hours. Clock-face timetables can be attractive for transport operators because the repeating pattern can allow the more efficient use of personnel, infrastructure and vehicles, and also make resource-planning easier.

Repeating timetables were first developed at the end of the 19th century, for local public transport, such as trams, rapid transit, and trains in the vicinity of large cities like New York City. A clock-face schedule is used currently for the New York City Subway system, the London Underground, and Merseyrail's Northern and Wirral lines.

Individual lines can have a regular schedule, even without connections to other lines. Nevertheless, it could be necessary to coordinate the schedules of different modes of transport if links are made between them, such as at the terminal stop of a tram network if a journey can be continued by bus, so that passengers don't have to wait too long at the transfer point until the next service arrives.

Clock-face timetables can be attractive even if services provide no connections to other public transport, because they allow a continuous use of vehicles and personnel.

Line-bound regular timetables are especially useful for lines with high service frequencies. If vehicles with the same destination follow each other in short intervals, transfer times are short even if there are delays. However, if the service intervals are 20 minutes or longer, it is important that schedules on each line are officially co-ordinated. One simple way of doing that is to shift the departure times of one of the lines to match the other.

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