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Transport - general

Jun 1, 2016

How big is the "transport divide" between inner and outer suburbs?

The “transport divide” between the inner and outer suburbs assumes time spent travelling increases significantly with distance from the city centre. But does it?

Average trip duration by mode (top) and purpose (bottom), Melbourne 2012/13 (source data: VISTA)
Average trip duration by mode (top) and purpose (bottom), Melbourne 2012/13 (source data: VISTA)

The average duration of a weekday trip in metropolitan Sydney across all modes and all purposes is 22 minutes and the average distance covered is 8.7 kilometres, according to the NSW Bureau of Transport Statistics. The Victorian Integrated Survey of Travel and Activity (VISTA) reports the corresponding numbers for meltropolitan Melbourne are virtually the same i.e. 23 minutes and 8.9 km respectively.

We know that both duration and distance differ significantly by mode and by purpose. For example, public transport trips in Melbourne take two to three times longer on average than car trips and cover more kilometres. Journeys to work take twice as long – and cover double the distance – as trips to the shops.

Another much cited difference is the “divide” between the inner city and the suburbs. It’s assumed by many that time spent travelling increases significantly with distance from the city centre.

But have a look at the first exhibit which shows trip duration by mode in metropolitan Melbourne. It can be seen the average trip actually takes much the same time in Melbourne’s inner, middle and outer rings i.e. between 22 and 23 minutes (see map of rings here).

This similarity holds for walking, cycling and for private vehicles. The latter is especially important, because private vehicles are the majority mode, accounting for 56% of trips in the inner ring, 73% in the middle ring and 81% in the outer ring.

The only significant difference in trip duration occurs in the case of public transport, where trips originating in the inner ring suburbs average 48 minutes and those in the outer suburbs average 68 minutes. The latter reflects the key use of trains for long trips to work and education destinations in the city centre.

The second exhibit shows average trip duration by purpose in Melbourne. Again, the differences between rings by trip purpose are pretty modest. That should be expected given the dominance of the car in all rings.

The third exhibit (below), however, shows that the difference between rings in terms of average distance travelled per trip (i.e. kilometres) is much larger, increasing with distance from the city centre. This reflects the faster travel speeds available further from the centre.

Thus due largely to express services, public transport users in the outer ring suburbs travel on average for about 40% longer than their counterparts in the inner city but travel 160% further in terms of kilometres. Low congestion means outer ring motorists travel half as far again in the same time as motorists in the inner ring.

Do outer suburban residents travel further because they want to or because they have to? Probably a bit of both, however theory suggests that when travel costs are low, activities tend to concentrate more to capture agglomeration benefits. Both residents and firms get the benefit of economies of scale and scope without spending more time travelling than their counterparts in the inner ring suburbs.

This is a fairly coarse scale. There would be bigger differences in travel time at a smaller scale e.g. if comparing travel by residents of the city centre (say) with the travel behaviour of residents in a particular outer suburb like Werribee.

Average trip distance (kilometres) by mode, Melbourne (source data: VISTA 2012/13)
Average trip distance (kilometres) by mode, Melbourne (source data: VISTA 2012/13)

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5 thoughts on “How big is the “transport divide” between inner and outer suburbs?

  1. Dylan Nicholson

    Has any research been done on why people spend so little time walking?
    It’s hard to understand why so many are prepared to spend over 60 minutes jammed into a train, but virtually nobody’s prepared to use the form of getting about our bodies are perfectly engineered for and indeed the only form available to us for most of human existence. Personally I *prefer* riding a bike, but if there was some particular reason I couldn’t and the choice was been, say, a 40 minute walk and a 15-20 minute drive, I’d definitely choose the former.

    1. drsmithy

      Because 40 minutes of walking might get you 3km away, but 60 minutes in a train or 20 in a car will get you anywhere from 10 to 50km ?

      Because it’s much more difficult to take kids to get a couple of days worth of groceries on foot ?

      1. Dylan Nicholson

        And yet Drsmithy in plenty of other countries plenty of people manage fine getting about largely on foot. But yes, obviously the number of people for whom walking the entire way between home and work is practical is going to be somewhat limited, but if the above graph is supposed to capture the total amount of *time* spent walking out of all trips, then I do wonder what it is that makes people feel they can’t just slow down a little and enjoy the chance at some fresh air and exercise, even if it means taking 10 or 20 minutes longer out of every day.

  2. Tony Morton

    Well observed Alan – we can see Marchetti’s Constant in action directly from the data.
    The other conclusion this points to is that there isn’t really any such thing as ‘time efficient urban form’ when there is universal access to high-speed transport. There’s only urban form that is more or less expansive in spatial terms. It confirms too that higher travel speeds have been no better at saving us time than higher productivity has been at reducing our working hours.
    Suburban development allows us to spread out with more land per person (assuming we can afford it) but at the expense of being dependent on cheap and ubiquitous high-speed transport to cover those greater distances within a fixed time budget. This leads to much higher transport-related energy consumption, as Newman and Kenworthy pointed out in the 1980s. Greater distances also tend to mean walking gets designed out of people’s lives, unless there’s adequate provision of high-speed transport modes like buses and trains that act as an extension of walking.
    Of course, concentration of activities also hits inherent limits in low-density suburbs as much as it does in high-density urban areas. It’s just that instead of being limited by the need to locate closer to residences, scale becomes limited by congestion and parking availability. Again, this can be overcome to some extent by provision for transport modes that reduce reliance on single-occupant cars.

    1. Oz (Horst) Kayak

      VATS 1994-2002, surveys with similar templates and algorithms to VISTA 2012/13 showed similar outcomes for MEL.

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