Looking closer at the transport & density debate

There’s a fascinating ongoing debate in planning circles about the question of how important density is to the likelihood of people using public transport (or a form of active transport, like walking and cycling). I’ve blogged about the issue a number of times before – particularly in terms of the argument put forward by Melbourne-based transport academic Paul Mees: that there are plenty of low density places in the world with good public transport, so we should focus on improving the PT and worry less about increasing density.

This argument seems to be supported by a basic look at the population density of various cities, and how that compares to the public transport usage in those same cities. The table below is an extract from data in Mees’s book: Transport for Suburbia (which, by in large, is excellent).

One limitation of the data above is how it looks only at the entire cities. Inevitably, one then gets into difficult situations working out where a particular city begins and where another one ends. Furthermore, the cities shown above have particular characteristics – aside from their density – that may play a particularly important role in explaining the relationship between their density and their PT use:

• Los Angeles has very dispersed employment patterns, and spent very little on improving public transport post World War II until relatively recently.
• New York’s employment is massively concentrated, plus benefits from a huge legacy rail network – almost exclusively constructed in the first half of the 20th century.
• Las Vegas has mainly grown in the past few decades, with much of its high density residences being in ‘gated communities’ isolated from the rest of the city.
• Vancouver made a deliberate policy decision many decades ago to not construct any freeways near its inner city.

Data that would perhaps be more useful than comparing the density and PT use between cities would be data that looks at different parts of the same city, and then analysed how the PT use in more dense parts of a city would compare with PT use in less dense areas. This work has, very helpfully, been done for a number of cities in NZ and in North America by Keith Hall – former CEO of the New Zealand Planning Institute. He has kindly emailed to me the presentation he gave at the NZPI conference the week before last (though it is a 21 MB document). A smaller version of the presentation, with all the words and numbers but without the pretty pictures, can be viewed here.

The first step in making such an analysis is splitting up the city into various ‘areas types’, depending on their level of employment/residential density. A table of how this division has been undertaken in an upgrade to New Zealand’s subdivision standards is shown below (modified further by Keith into sub-categories to provide a more fine-grained result):

When you start to overlay the level of PT use and active transport with the measure of land-use intensity, at least in Auckland there seems to be a fairly obvious connection between the two: It’s interesting to note that the above table is based on 2001 census data. With the big upswing in PT usage over the past few years – particularly in ‘Rapid Transit’ usage (the train system and the Northern Express), which often serves outer areas particularly well – it could be quite fascinating to see whether these trends have changed at all.

Looking at detailed data for Toronto, one can see the same trends emerging – although generally at a higher level of PT use all around. Interestingly, it is employment density that seems to be related to PT use to an even greater extent than population density: One particularly useful thing Keith does with this data is make a number of comparisons across cities – which not only shows that there seems a relationship between PT use/active transport and the percentage of the population living in relatively high densities, but also gives a really good indication of ‘over-performing’ and ‘under-performing’ cities in terms of their PT use and active-transport use. As can be seen in the graph below, Auckland is (or was at least) quite clearly an under-performing city. Clearly a result of the near complete lack of investment in public transport for nearly 60 years following World War II:

It’s promising to see Wellington performing so extremely well – for a given level of density it seems that Wellingtonians are much more likely – on average – to take public transport, walk or cycle to work than most other cities.

Ultimately, my feeling is that density does matter when it comes to PT use – particularly employment density. However, in the case of Auckland this doesn’t mean the “city is too spread out for PT to work” – as is often the claim. The graph above clearly shows that Auckland under-performs (or at least did when the data collection was done) in terms of PT and active transport modeshare for its density. In other words, we can achieve a lot without having to up our density – but if we really want to increase PT use significantly, one of the best ways to do that is to have more of the city (particularly more of the employment) in areas that have a density much higher than what most of Auckland has now.

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