melbourne in transit

A blog about public transport network design and operation, covering topics such as route structures, services, passenger information, marketing and more.

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Saturday, June 11, 2005

Harmonised and clockface timetables

Once a bus route has been designed the next task is to design a timetable, taking into account things like the route's importance, its likely patronage, connections with trains, user-friendliness, service reliability and resources (buses and drivers) available.

Harmonised headways

Except in peak times, suburban trains and trams run to a regular headway or frequency. On busy bus routes that provide an important link between railway stations and major trip generators that are off the rail network, buses should run at the same intervals as trains. This provides reliable connections.

* A hypothetical harmonised timtable

A bus timetable that has been co-ordinated with train arrival times looks like this:

Train arrives A - Bus departs A
10:05am ----------- 10:10am
10:20am ----------- 10:25am
10:35am ----------- 10:40am
10:50am ----------- 10:55am

Notice that it has constant waiting times, so that passenger can jump on any train and know that there will be a good bus connection. And there'll be no need to rush to a particular train as all will provide a good connection. If a train is narrowly missed, the next one will arrive in 14 minutes.

Total journey time is a constant 30 minutes, assuming a 15 minutes on the train, 10 minutes on the bus and 5 minutes transfer time. Passengers get a reliable fast trip (proportion of total travel time in motion 83%/waiting 17%) and are saved from juggling (or even carrying) timetables.

* A hypothetical unharmonised timetable

An unharmonised bus timetable that has not been co-ordinated with train arrival times looks like this:

Train arrives A - Bus departs A
10:05am ----------- 10:10am
10:20am ----------- 10:30am
10:35am ----------- -
10:50am ----------- 10:50am

The bus connection from the 10:05 train is good, but passengers on the next two trains need to wait 10 and 15 minutes respectively. It's even worse for passengers arriving at 10:50, who might see their bus depart (with almost no passengers on board) as they leave the train. They must then wait 19 minutes for the next bus at 11:10am.

For what should be a reliable 30 minute trip, travel time can be as high as 45 minutes. In this case the time in motion is a low 55% and the waiting time a high 45% of the total trip time.

Though the train service in both examples runs every 15 minutes, the effective service frequency for people making this rail-bus journey is reduced in this last example. Of the four trains an hour, only two offer a satisfactory connection.

If the train arriving at 10:30am is missed, then a 44 minute wait until the next satisfactory connection (11:05am arrival) is required. This wait is more than triple the 14 minute maximum wait required in the first example.

* A hypothetical harmonised timetable for a local route

Train arrives A - Bus departs A
10:05am ----------- 10:10am
10:20am
10:35am ----------- 10:40am
10:50am

This example would be suitable for a quiet local route where buses are timed to meet every second train. Though inferior to the 15 minute service, passengers still know that good connections are ensured from every second train.

Even though there are fewer buses than in the above (unharmonised) example, the maximum waiting time for trains that provide a good connection is 29 (not 44 minutes) and their arrivals are at even clockface intervals. As with the non-harmonised example above, the maximum wait for a bus is 20 minutes.

Comparing these two examples show that where trains run every 15 minutes, there is comparatively little benefit to be gained by increasing bus services from a harmonised 30 minute to a non-harmonised 20 minute headway. In contrast, going from 20 to 15 minutes is a massive improvement that should see patronage soar.

This also means that if two nearby bus routes run every 20 minutes, upgrading one to every 15 minutes and downgrading the other to every 30 minutes would vastly improve one while only slightly degrading the other, leading to a net benefit.

* A composite harmonised timetable for two local routes that serve a common road

Two less frequent routes that follow the same road for much of their trip can be timed to provide a frequent and connecting service for people living along that road. The presentation of passenger information on such routes is discussed in the section on composite timetables.

Train arrives A - Bus departs A
10:05am ----------- 10:10am (Route 200)
10:20am ----------- 10:25am (Route 201)
10:35am ----------- 10:40am (Route 200)
10:50am ----------- 10:55am (Route 201)

* Rules and limitations of harmonised headways

The main rule when harmonising headways is that the service frequencies must be multiples of one another. Hence a bus service running every 15 minutes can provide good connections with a train system where the basic service frequency is also every 15 minutes. Buses running every 30 minutes can also provide predictable connections for quieter routes. However feeder buses running every 20 minutes trying to connect with trains running ever 15 minutes (or vice versa) are inefficient and are unlikely to attract maximum patronage.

Harmonised headways are a necessary but not sufficient condition for good connections. At their worst they can mean that bus running every 15 minutes consistently misses a bus also running every 15 minutes.

However improving a connection when headways are harmonised normally involves only a minor tweaking of the timetable (starting all services 5 minutes later or earlier) rather than wholesale changes.

Harmonised headways are of utmost importance when buses are infrequent and/or fulfil a feeder role for trains. As demonstrated here, moving from a non-harmonised to a harmonised headway system can dramatically cut travel times and make the service more attractive.

The main limitation with harmonised headways is that especially where a long bus route serves multiple railway stations, it may not be possible to obtain good connections with each service. Nevertheless it provides a predictabilty of travel that is absent when trying to connect 15 minute trains with 20 minute buses.

Also timetable harmonisation becomes less important when services are less than 10 minutes apart, such as with peak-hour trains and trams. In these circumstances, active transfer management (eg alerting bus drivers of details of arriving trains) may become more desirable to provide efficient transfers.

Clockface (or memory) timetables

Ideally passengers want to be able to travel without a timetable. This means frequent or at least regular timetables so that departures are the same minutes past the hour at all times.

The following service frequencies are clockface: 5, 6, 7.5, 10, 12, 15, 20, 30, 60 minutes. Services will be at the same minutes past the hour so people will be able to memorise them.

The following service frequencies are not clockface: 17, 25, 35, 40, 45, 50 minutes. Passengers are unlikely to be able to memorise the times for these services.

Perth train timetables represent one of the the purest examples of clockface timetabling. Sunday and evening services run every 30 minutes, whereas weekdays are every 15 minutes. It appears as if the planners started with a base 30 min Sunday timetable and added services in between to provide a 15 minute service six days a week. All passengers do is to remember a certain number of minutes past the hour and (peak times excepted) will then know all times for their station without carrying a timetable.

When planning services, clockface timetables should be encouraged and non-clockface timetables are discouraged. The only exception where non-clockface times may be desirable is to provide connections with other services. The most frequent example is when trains are every 20 minutes and a service meeting every train cannot be provided. In this case a non-clockface 40 minute service frequency may be required to provide connections, and is arguably preferable to a 60 minute (clockface) service.

* A harmonised and clockface timetable: Perth's Circle Route















Day/TimeTrain98/99 busHarmonised?Clockface?
M-F 6am - 9am5 - 10 min15 minn/a*yes
M-F 9am - 4pm15 min15 minyesyes
M-F 4pm - 6pm5 - 10 min15 minn/a*yes
M-F 6pm - 7pm15 - 30 min30 minyesyes
M-F 7pm - 9pm30 min30 minyesyes
M-F 9pm - 12am30 minno service--
Sat 6am - 7am15 min30 minyesyes
Sat 7am - 5pm15 min15 or 30 min**yesyes
Sat 5pm - 7pm15 min30 minyesyes
Sat 7pm - 12am30 minno service--
Sun 8am - 7pm15 or 30 min**15 or 30 min**yesyes
Sun 7pm - 12am30 minno service--


(*) In these cases exact timetable co-ordination is not possible, but service frequencies are mostly sufficient to keep waiting times down.

(**) At these times some rail lines and a section of the Circle Route operate every 15 minutes.

98/99 is an orbital route that provides inter-suburban and rail-feeder services. Apart from the somewhat limited operating hours, the timetable is very user-friendly, with a great effort made to co-ordinate services, harmonise headways and use memory (clockface) timetables.

* Headway harmonisation and clockface timetabling of Melbourne's proposed Route 700 Smartbus timetable
















Day/TimeTrain700 busHarmonised?Clockface?
M-F 5am - 9am3 - 10 min6 - 15 minn/a*no
M-F 9am - 4pm15 min12-19 minpartial**no
M-F 4pm - 6pm3 - 10 min8 - 18 minn/a*no
M-F 6pm - 8pm10 - 30 min13 - 18 minn/a***no
M-F 8pm - 12am30 min20 - 30 minmostlymostly
Sat 6 - 11am20 min30 minnoyes
Sat 11am - noon20 min15 minnoyes
Sat noon - 6pm20 min20 minyesyes
Sat 6pm - 12am30 min30 minyesyes
Sun 7am - 11am30 min31 - 35 minnono
Sun 11am - 7pm20 min31 - 35 minnono
Sun 7pm - 9pm30 or 40 min30 - 37 minnono
Sun 9pm - 12am30 or 40 minno service--


(*) In these cases exact timetable co-ordination is not possible, but service frequencies are mostly sufficient to keep waiting times down.

(**) The average service frequency (every 15 minutes) matches the trains, but the non-constant headways do not.

(***) Due to variations in train headways during these shoulder periods, headway harmonisation would not be possible. Active transfer management is suggested instead, especially for trains from the city.

In contrast to Perth's Circle Route, which is harmonised and clockface at all times, Saturday afternoons and evenings are the only times where Route 700 services are consistently harmonised and clockface. On weekdays the average headway is appropriate, but is too irregular to be a genuine 'memory' timetable. On Saturdays, both the 30 minute morning and the 15 minute pre-noon services are wasted because though both are clockface, neither consistently connect with trains. Sundays see neither clockface nor harmonised service.

This exercise demonstrates that though proposed service levels are mostly sufficient, they are not necessarily arranged to provide the best and most reliable connections. The use of harmonised and clockface timetables as recommended here has the potential to make Route 700 to become a genuinely smart service that people will wish to use.

Conclusion

Harmonised and clockface timetabling has a big role to play in making public transport more reliable, faster and easier to use. A Perth-style review and revision of bus schedules to improve co-ordination is recommended, starting with the premium Smartbus services.

3 Comments:

Anonymous chris said...

A wonderful post!!

You wouldnt be able to forward that brilliant logic to the clowns at the Department of Idiots could you?? Apart from showing their ineptness (DoIneptness) they may actually learn something from it!

Unless they decide that they will 'improve' it as they try to do with many tasks...

Great work Peter!!

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