Friday, March 11, 2011

More Aural timetables: analysing individual route connections

It's been a busy week in Melbourne transport; trains off the rails at sidings, disruptions due to power glitches, new fares and major events in the city this weekend. Nevertheless I'm still doing the timetable beat thing, and here's the latest.

Earlier experiments emphasised headway harmonised networks. If the network was frequency harmonised it would produced a nice rhythm, repeating in as little time as possible. An unharmonised network would sound more random, with no dominant rhythm, or a longer rhythm with the same connections only repeating every couple of hours.

Harmonised headways is a necessary but not sufficient condition for good connectivity. A bus matching a 20 minute rail service isn't good if it departs as the train is pulling in.

What is really important is the waiting periods between when the train arrives and the bus departs. Too short and it means a missed connection, especially if the train is running late. Too long and the bus is no faster than walking.

This part quietens down the pulse (but it's still there if you listen hard) and emphasises the waiting periods. It does this by applying a tone for the duration of the wait (again 60 min = 1 second, 6 min = 0.1 second).

Because the human hear is more sensitive to pitch than duration, I also used different pitches. I went for three pitches only (low, middle and shrill) to aid recognition. A low pitch is a long wait (>15 min), a medium pitch a medium wait (5-15 min) and a shrill pitch is a short wait (<5 min) which also risks being a missed connection if the train is late. I'd have liked to differentiate between a near-ideal 6 min connection from a longish 14 min connection, but that would have meant another tone which slows recognition. So I stuck with three. Music afficiondos will hear that I've used notes - something I intend to keep doing with future aural timetables.

At the end I've got a comparison between the harmonisation possible between 20 min/38 min frequencies and 20 min/40 min frequencies. The tonal difference is quite stark. Even though it's a slighly lesser frequency, a well-timed 40 min service can provide predictable connectivity is scheduled carefully, whereas a 38 min service has a plethora of good, bad and just missed connections, happening at seemingly random intervals.

There haven't been many comments on this, so whether you think aural timetable have potential or are just a useless curiousity, they'd all be welcome here.

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