At the top level of the Region as a whole, in 2018 17.3% of people aged over 15 years who work, usually took the bus, train, ferry, walked or cycled as their main mode of travel to work This is up from 13.5% in 2006.
Looking at the 2018 data for BTFWC at the Local Board level, and arranging Local Boards (apart from Waitakere, Waiheke and Great Barrier Island) roughly north to south results in the pleasing ‘Mt Taranaki’ type profile set out in Figures 1 and 2.
Figure 1: % of work trips by bus, train, ferry, walking and cycling - 2018
As distance from the centre increases, then the proportion of work trips by BTFWC drops, with a similar pattern either side of the CBD.
If we look at the pattern over the period 2006 to 2018, then the central Waitemata Local Board area saw more of a lift in BTFWC trips than the outer Boards. See Figure 2.
Figure 2: % work trip by bus, train, ferry, walking and cycling 2006, 2013, 2018
The central Waitemata Local Board area has seen BTFWC climb from 38.8% of work trips in 2006 to 52.6% in 2018. At the other end of the Region, the Rodney Local Board area has gone from 6.1% to 5.6%, or a relative decline in other words (although this may because the census questions varied between the different censuses).
A Local Board area level of analysis is fairly coarse, and a more fine-grained level may help to highlight more specific trends, but at a strategic level, the Local Board level is not a bad place to start. Also, the main means of travel to work variable is rated as moderate quality by Stats NZ and caution is advised when using this variable at small geographies.
So far, so good.
Now let’s look at where the new housing has located over the period 2013 to 2018.
The census records an increase of over 60,000 dwellings during the five years between 2013 and 2018.
If this data is arranged by Local Board area, again roughly north-to south, the we get a ‘triple peak’ outline, rather than the single peak of the BTFWC travel to work data.
Figure 3: Additional dwellings by Local Board 2013-2018
The northern outer suburbs saw a big increase, as did the central area, and the southern edge. The inner and middle suburbs took limited growth. If we match that picture up with the % of work trips by BTFWC, then the miss match is evident.
Figure 4: Mode of travel (2018 - right hand side) and new housing (2013 -2018- left hand side).
But of course, this miss-match makes sense. As distances from the centre increase, and transport costs rise (both private vehicle use and passenger transport services), then land and house prices should fall, making the edge more attractive for new housing.
It is tempting to look at the ‘gap’ either side of the central area and to speculate what would have been the transport outcomes if the region saw a more even pattern of housing growth between 2013 and 2018. That is, new housing occurred roughly in-line with the share of dwellings in the Local Board areas, as of 2013. This could be called a 'fair share' approach to growth. Perhaps not a totally realistic approach, in that some Local Board areas may be less able to cope with growth than other areas (for example Local boards with extensive areas of heritage housing). Nevertheless, a fair share approach is a relevant policy approach.
If the new housing between 2013 and 2018 was allocated to each Local Board area based on the share of housing as of 2013, then we get the pattern in Figure 6. The outer Local Board areas see less housing and the middle and inner Local Board areas see more. The central Waitemata Local Board area has less growth.
Figure 6: Additional dwellings 2013-2018, actual and reallocated.
The three peaks get flattened out, and the outline is more like a rolling landscape.
This is a very simplistic approach to reallocation, as household types vary between the different Local Board areas. Typically, the south sees larger number of people per dwelling, and so will have more trips per dwelling than smaller households on the North Shore, for example.
We can then compare the number of work trips generated by the reallocated ‘fair share’ pattern versus the actual pattern and see what difference that makes.
To do so, I first need to work out the number of work trips generated by each dwelling in each Local Board area; broken down into the number of BTFWC trips and the number of trips made by people in cars, on a per dwelling basis.
Figure 7: Work trips per 100 dwellings, 2018
Figure 7 shows the pattern. The Mt Taranaki profile of BTFWC trips is again apparent. Vehicle trips have a central “V” shaped valley profile. What is interesting is that vehicle trips rates are reasonably similar, across the Local Board areas, outside of the central area. The length of trips (kilometres travelled) may be greater, but the number of trips is similar. There is a bit of a rise in the south.
I can now compare the number of work-related vehicle trips and the number of BTFWC trips under the two scenarios: that is as per actual pattern of growth 2013 to 2018, and the re-allocated pattern. Table 1 sets out the estimate of trips.
Table 1
Under the fair share scenario with more dwellings in the middle and inner suburbs, the number of vehicle trips goes up, not down! The number of BTFWC trips increase marginally. Partly this increase in vehicle trips is due to fewer dwellings in the central Waitemata Local Board area and more dwellings in adjacent Local Board areas that have higher rates of vehicle use (and which also see more BTFWC trips). So maybe there is a logic to the observed growth patterns?
What the analysis doesn’t tell me is whether the greater population density in some areas helps supports more bus or train services, for example, or if congestion is better or worse. What it does tell me is that changing transport patterns through changes to urban form is hard work and likely takes a long time.
Next I want to do the same exercise, but this time in relation to destinations (that is, workplaces).
