Sunday, May 09, 2010

Effective Frequency - a measure of timetable co-ordination

One of this blog's hobbyhorses, that of timetable co-ordination, made it into today's Age. Not only that but it even got a one-liner on Gold 104 News (heard while travelling on the 901 SmartBus if anyone asks).

The above link has a spreadsheet prepared by the PTUA. There is also a web application showing average connectivity by route and station (note: timetable data from last year).

More buses and timetable co-ordination were cited as ways to improve connectivity. Though the article focused on buses, train frequency can also be part of the solution, especially in outer areas where hourly minimum standards buses cannot connect with trains every 40 minutes and middle suburbs where SmartBus and train frequencies don't always match.

Average connection times provide a rough guide, but as they say, 'your connection may vary'. Provided headways are fairly constant (which they are for most services), a measurement method I like is the concept of 'effective connected service frequency', most commonly for a suburban bus feeding a city train.

Let's take Route 436 at Werribee, a local route that scored well for connectivity. As the service is headway harmonised with trains throughout the day and connections are good, the effective connected service frequency of a train+bus trip is the same as the bus route's individual frequency (in this case 40 minutes) seven days per week. This is how it should be for an effective network.

A similar suburb to Werribee, but in Melbourne's north, is Craigieburn. However its buses operate at frequencies incompatible with trains. Therefore passengers need to be choosy about what services to catch to minimise waiting.

A sample of Saturday train/bus times ex city are as follows:

Train arrives 9:52am

Bus 528 departs 9:57am

Train arrives 10:12am

Bus 528 departs 10:27am

Train arrives 10:32am

Train arrives 10:52am

Bus 528 departs 10:57am

Train arrives 11:12am

Bus 528 departs 11:27am

Train arrives 11:32am

Train arrives 11:52am

Bus 528 departs 11:57am

With a 10 minute maximum waiting time allowance, the effective connected service frequency is only 60 minutes (connecting services shown in bold), despite each part of the network operating more frequently. Even though Werribee's local buses are less frequent than Craigieburn's, Werribee's effective frequency is higher due to better connectivity. Werribee passengers get a good connection every second train, but for Craigieburn it's every third train (this is on weekends, on weekdays Werribee has a higher train frequency).

Pakenham on weekends has similarities to Craigieburn. The difference here is that the frequencies are halved - trains every 40 minutes and buses every 60 minutes. The effective connected service frequency ends up being two hours because of unharmonised scheduling. Not exactly attractive for your discretionary passenger, and inferior to the planned connectivity that hourly minimum standards routes were intended to give.

Everyone knows that frequency is key to attracting patronage. At the same time buses cost money to run, so it is not always possible to deliver the highest frequency.

However effective service planning requires that the effective connected service frequency is no worse than feeder bus frequencies to maximise network connectivity and thus patronage. Not doing so means that taxpayers are paying for a higher service frequency than can be realised and passengers are getting a lower overall frequency than ought to be possible given the number of buses on the road.

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