Census Journey to Work | Charting Transport

How has motor vehicle ownership changed in Australian cities for different age groups?

Sun 18 July, 2021

Motor vehicle ownership has a strong relationship with private transport mode share, and has recently seen declines in some Australian cities (e.g. Melbourne). In addition, we know that younger adults more recently have been deferring the acquisition of a driver’s licence (see: Update on Australian transport trends (December 2020)), so have they also been deferring motor vehicle ownership? For which age ranges has motor vehicle ownership increased and decreased? How might this have influenced journey to work mode shares? And how do changes in motor vehicle ownership relate to changes in driver’s licence ownership?

This post aims to answer those questions for Australia’s six largest cities, primarily using 2011 and 2016 census data, but also using household travel survey data for Melbourne.

But first…

A quick update on motor vehicle ownership trends in Australia

As I was writing this post, ABS released data for their Census of Motor Vehicle use – January 2021 (sadly the last motor vehicle census run by the ABS). I’ve matched this up with the latest available population data, and found a small but significant uptick in motor vehicle ownership rates in all Australian states in 2021 following the onset of the COVID-19 pandemic:

I suspect this uptick will be at least partly due to a massive reduction in immigrants into Australia – who I’ve recently found to have much lower rates of motor vehicle ownership for the first few years they live in Australia (see Why were recent immigrants to Melbourne more likely to use public transport to get to work?) and also probably low motor vehicle ownership – see How and why does driver’s licence ownership vary across Sydney?).

It could also reflect a mode shift from public to private transport, as people seek to avoid the perceived risk of COVID-19 infection on public transport.

But there’s another likely explanation of this uptick and it relates to ages, so keep reading.

What does household travel survey data tell us about motor vehicle ownership by age in Melbourne?

My preferred measure is the ratio of household motor vehicles to adults of driving age (notionally 18 to 84).

Using Melbourne household travel survey data (VISTA), I can calculate the average ratio by age group pretty easily, and the following chart also breaks this down for parents, children, and other people (living in households without parent-children relationships):

With 2-year age bands there is a limited span of age ranges for some categories due to the small survey sample sizes (I’m only showing data points with 400+ people). So here is a similar chart using 4-year age bands, which washes out some detail but provides values for wider age ranges:

You can see some pretty clear patterns. Motor vehicle ownership was high for households with children (peaking for ages 12-13), parents – particularly in their late 40s, and those aged in their 50s and early 60s in households without children. Average motor vehicle ownership was lowest for young adults living away from their parents, and for those in older age groups.

Unfortunately the VISTA dataset isn’t really big enough to enable significant analysis of changes over time – the sample sizes for age bands get too thin when you split the data over years or even groups of years. I’d like to understand changes over time, so…

What can census data tell us about motor vehicle ownership by age?

Unfortunately it’s not possible to calculate the ratio of household motor vehicles to adults using Census (of Housing and Population) data (at least when using ABS Census TableBuilder).

The numerator is pretty easy for the 2011 and 2016 censuses which classify private dwellings as having zero, 1, 2, 3, 4, …, 28, 29, or “30 or more” motor vehicles. Only a very small number of households report 30+ motor vehicles. Unfortunately the 2006 census’s top reporting category is “4 or more” motor vehicles which means you cannot calculate the motor vehicle ratio for many households.

My preferred denominator – the number of adults of driving age – is not available in ABS’s Census TableBuilder. The closest I can get is the “number of persons usually resident” for dwellings – and private dwelling are classified as having 1, 2, 3, 4, 4, 5, 6, 7, or “8 or more” usual residents in the 2006, 2011 and 20216 censuses. Obviously I cannot calculate the ratio of motor vehicles to usual residents if there were “8 or more” usual residents.

(For the census data nerds out there: I tried to get a good guess of adults by using family composition, but it can only distinguish parents (who may or may not be of driving age), children under 15, and dependent students aged 15-24. And worse still, that doesn’t work for multi-family households, and you cannot filter for single family households as well as distinguish family types.)

So I’m stuck with household motor vehicles per person usually resident. And an obvious drawback is that motor vehicle ownership will be lower for adults living in households with children, compared to those without children.

Here’s the distribution of motor vehicle : household size ratios for Greater Melbourne for 2011 and 2016 (I’ve left out 2006 because too many households cannot be calculated). There are a lot of different ratio values, but only about a dozen common ratios, several of which I have labelled on the chart.

Sure enough, there were much lower ownership ratios for children’s households, and adult ages where children were more likely to be resident (generally mid-20s to around 60). Higher ratios peaked for people in their early 60s and then steadily declined into older ages, with most people in their 90s living in dwellings with no motor vehicles (if they are not living in non-private dwellings). For adults in their 60s, one car per person was the most common ratio.

I can also calculate the average motor vehicle ownership ratio for each age as an aggregate statistic (excluding 3-4% of households where I don’t know the precise number of residents and motor vehicles). Here’s how that looks for 2011 and 2016:

As mentioned, I cannot calculate this ratio for households where I don’t know the precise number of both motor vehicles and usual residents (or where I don’t know the number of usual residents, but do know there were zero motor vehicles). Across Australia’s five biggest cities that’s 4.1% of population in the 2016 census, 3.4% in 2011, and 10.4% in 2006 (but much higher proportions of younger adults). They sound like small numbers, but aren’t that small when you consider the shifts in ownership between censuses.

But there is another way to classify households with fewer unknowns – whether they have:

no motor vehicles;
fewer usual residents than motor vehicles; or
at least one motor vehicle per usual resident.

The benefit of this approach is that you can classify almost half of the households where you cannot calculate an exact ratio:

If a household had 30+ motor vehicles (very rare) but fewer than 8 usual residents, then it had at least one vehicle per person.
If a household had 4+ motor vehicles (quite common in 2006 census) and 4 or fewer usual residents, then it had at least one vehicle per person.
If a household had 8+ usual residents (about 1.3% of population in 2016), but 7 or fewer motor vehicles (93.5% of the 1.3%), then it had less than one vehicle per person.

Across Australia’s biggest five cities I can now classify all but 2.5% of the 2016 population, 2.3% of the 2011 population and 6.1% of the 2006 population.

The next chart shows the distribution of this categorisation for Melbourne (using Melbourne Statistic Division for 2006, and “Greater Melbourne” for 2011 and 2016). I’ve put the remaining people living in uncategorisable households (“unknown”) in between 0 and <1 motor vehicles per person, as it is likely households who did not answer the question about household motor vehicles probably had few or no motor vehicles (refer to the appendix at the end of this post for more discussion).

I have also removed people who did not provide an answer to the usual residents question (hoping they are not overly biased – they are probably households who didn’t respond to the census), and non-private dwellings (where motor vehicle ownership is not recorded).

The patterns are similar to the previous chart, with a double hump pattern of 1+ motor vehicles per person. There are some changes over time, which I’ll discuss shortly.

Unfortunately the unknown band is still pretty wide in 2006 – in fact I still cannot categorise around 15% of 20 year olds in 2006 (many must have lived in households with 4+ motor vehicles), so it doesn’t really support good time series evaluation between 2006 and 2011.

So how has motor vehicle ownership by age changed over time in Melbourne?

Many of the previous charts were animated over 2-3 censuses but there’s a lot of take in with different lines moving in different directions for different age groups. To help to get better sense of those changes, what follows are a set a static charts, and then some discussion summarising the patterns.

Firstly, the change in average motor vehicles per usual resident for each age year (but only for households where the exact number of motor vehicles and usual residents is known):

Secondly, here’s a static chart that shows the proportion of population living in households known to have 1+ motor vehicles per person for both 2011 and 2016 for Melbourne, and the difference between 2011 and 2016 (I’ve excluded 2006 as there were too more unknowns). I haven’t removed uncategorisable households from the calculations, on the assumption they bias towards lower motor vehicle ownership (as discussed above).

This chart shows very little change for children under 18, but also very few such households had 1+ motor vehicle per occupant in 2011 or 2016 so it’s not a very useful metric. Lower ownership ratios are much more common for households with children, so here’s a chart showing the proportion of the population living in dwellings with at least 0.5 motor vehicles per person, and the change between 2011 and 2016: (I used equivalent rules to classify households with 8+ usual residents or 30+ motor vehicles, where possible)

And finally, here’s a chart showing the proportion of the population living in dwellings reported to have no motor vehicles (probably an underestimate as I think many “not stated” responses are likely to be zero motor vehicles).

Each of these charts paints a similar picture. Here’s a summary by age ranges:

Age range	Motor vehicle ownership trend
0-17	Slight increase
18-26	Certainly a decline, including around 1-2% more people living in dwellings with no motor vehicles.
27-45	Small decline of around 2-3% living in households with 1+ or 0.5+ motor vehicles per person. But there was no significant increase in households with no motor vehicles, and average motor vehicles per person was relatively stable.
46-64	Very small decline (around 1%) of people living in households with 1+ and 0.5+ motor vehicles per person, but little change in households without motor vehicles.
65+	Significant increase in metrics of motor vehicle ownership, and a significant decline in dwellings without any motor vehicles.

So while overall motor vehicle ownership in Melbourne declined between 2011 and 2016, it was mostly in working aged adults, partly offset by family households and older adults increasing their rates of motor vehicle ownership.

And going back to the uptick in motor vehicle ownership in January 2021… recent immigrants to Australia have skewed towards young adults (particularly through skilled migrant visas). The massive reductions in immigrants in 2021 will mean the population contains proportionately fewer young adults – who generally have low car ownership, particularly recent immigrants. This slightly but significantly smaller number of young adults will no longer be fully offsetting those over 70 who are increasingly retaining motor vehicles longer into their life.

What about other Australian cities?

As above, I’ll present a series of charts showing the various metrics then summarise the trends.

Firstly, a chart showing the average ratio of motor vehicles per resident by age for all cities between 2011 and 2016 – for private dwellings where the exact number of vehicles and usual occupants is known:

To help see those changes, here is a static chart showing the change in average motor vehicles per person by age (I’ve used three-year age bands as the data otherwise gets a bit too noisy):

Here’s an animated chart showing the percentage of people living in private dwellings with 1+ motor vehicle per person:

There’s a lot going on in that animation (and the data gets a bit noisy for Canberra due to the relatively small population), so next is a chart showing the difference in population living with 1+ motor vehicles per usual resident:

As before, the threshold of 1 motor vehicle per person is not useful for examining the households of children, so here’s a similar change chart for the 0.5 motor vehicles per person threshold:

These difference charts mostly form duck-shaped curves with a slight increases for children, a mixture of increases and decreases for working aged adults, and a large increase for older adults (particularly for those in their 70s).

For young adults (18-30), motor vehicle ownership mostly declined in Melbourne and Canberra, but for Perth and Adelaide there was a large increase in ownership for those aged 21-39.

There was less change in ownership for those aged 40-54. On the metrics of proportion of population with 1+ and 0.5+ motor vehicles per resident there was a small decline in all cities, but for average motor vehicles per person, some cities declined and some increased. So perhaps the amount of variation in motor vehicle ownership narrowed in this age range.

Melbourne was mostly at the bottom of the pack, with Brisbane, Adelaide or Perth mostly on top.

To continue this analysis, I want to know whether these changes in motor vehicle ownership might be impacted mode share, but first we need to look at…

How did journey to work mode shares change by age?

Here are public transport mode shares of journeys to work by age for Australia’s six biggest cities, 2006 to 2016:

Public transport mode shares were much higher for younger adults in all cities in all censuses. Most cities rose between 2006 and 2011, but then different cities went in different directions between 2011 and 2016.

Here’s the mode shift between 2006 and 2011:

Most cities and ages had a mode shift towards public transport, particularly for those aged around 30, but less so for young adults.

Here’s the mode shift between 2011 and 2016:

Between 2011 and 2016 there was a mode shift to public transport in most cities for people in their 30s and 40s, but for younger adults there was a decline in public transport mode share in most cities, with only Sydney, Melbourne, and Canberra seeing growth.

However we are talking about motor vehicle ownership, and declining motor vehicle ownership may be because of mode shifts to walking, cycling, and/or public transport. So it is worth also looking at private transport mode shares (journeys involving private motorised modes but not public transport modes).

To help see the differences, here is the mode shift for private transport 2006 to 2011:

There’s a similar curve for all cities, but different cities are higher or lower on the chart. There was a shift towards private transport for young workers, a shift away in most cities for those in their 20s and 30s, and smaller shifts for those in their 40s and 50s

And from 2011 to 2016:

Again similar curves across the cities, with younger adults again more likely to shift towards private transport in most cities, a big shift away from private transport for those in their 30s and early 40s in Sydney and Melbourne, and smaller shifts for those in their 50s and 60s.

What’s really interesting here is that the mode share and mode shift curves are similar shapes across most cities (except the much smaller city of Canberra). There are some age-related patterns of travel behaviour change consistent across Australia’s five biggest cities.

How did changes in motor vehicle ownership compare to changes in private transport mode share?

If motor vehicle ownership increases you might expect an increase in private transport mode shares, and likewise you might expect a decrease in ownership to relate to a decline in private transport mode shares.

Indeed when you look at cities as a whole, there is generally a strong relationship between these measures, although different cities moved in different directions between 2011 and 2016.

In this post I’m interested in shifts for people in different age groups. The following chart shows the changes in motor vehicle ownership and private transport mode shares for each city and age group: (note different axis scales are used in each row of charts)

However I’m particularly interested in the change in these factors, rather than where they landed in each of 2011 and 2016. So the following chart plots the change in motor vehicles per 100 persons and the change in private transport mode share of journeys to work between 2011 and 2016 for five-year age bands (noting that of course every living person got five years older between the censuses).

That’s a busy chart but let me take you though it.

There’s one mostly empty quadrant on this chart (top-left): for no city / age band combinations did motor vehicle ownership decline but private transport mode share increase, which isn’t really surprising.

But in city / age band combinations where motor vehicle ownership did increase there there wasn’t always an increase in private transport mode shares – quite often there was actually a decline. So increasing motor vehicle ownership doesn’t necessarily translate into higher private transport mode shares – for journeys to work at least. Perhaps increasing affordability of motor vehicles means more people own them, but don’t necessarily switch to using them to get to work.

The largest declines in private transport mode share occurred in city/age band combinations that actually saw a slight increase in motor vehicle ownership.

The cloud is quite spread out – which to me suggests that motor vehicle ownership is probably not a major explanation for changes in mode share between 2011 and 2016 – there must be many other factors at play to explain changes in mode shares across cities. Indeed, see my post What might explain journey to work mode shifts in Australia’s largest cities? (2006-2016) for more discussion on these likely factors.

What is the relationship between motor vehicle ownership and driver’s licence ownership?

As I’ve previously covered on this blog (eg see: Update on Australian transport trends (December 2020)), data is available on the number of licenced drivers by different age groups, but only at the state level.

I’d prefer not to be using state level data as city and country areas might wash each other out, but I’d don’t have a lot of choice because of data availability. (Licencing data is available at postcode resolution in New South Wales (see How and why does driver’s licence ownership vary across Sydney?), but unfortunately you cannot disaggregate by both geography and age.)

Here’s another (busy) chart showing the relationship between licence and motor vehicle ownership by age band and city, across 2011 and 2016:

The main thing to take away here is that most of the points are within a diagonal cloud from bottom-left to top-right – as you might expect: there is less value having a driver’s licence if you don’t own a car, and little point owning a car if you don’t have a licence to drive it. The exceptions to the diagonal cloud are mostly age bands 30-39 and 40-49, where the average motor vehicle ownership rates are lower because many of these people often have children in their households, and I cannot remove children from the calculation using census data.

But I can control for the issue of children by going back to city geography by using household travel survey data for Melbourne (VISTA, 2012-2018). The following chart shows the relationship between average motor vehicle and driver’s licence ownership for adults by different age brackets.

The data points again generally form a diagonal cloud as you’d expect. Higher motor vehicle ownership generally correlates with higher licence ownership.

The change in ownership rates by age are interesting. Children under 10, on average, lived in households where adults have very high levels of motor vehicle and licence ownership. Licence ownership was slightly lower for adults in households with children aged 10-17 (although this could just be “noise” from the survey sample). Young adults (18-22) then on average lived in households with relatively low motor vehicle and licence ownership. As you move into older age brackets licence ownership increased, followed by increases in motor vehicle ownership, with both peaking again around ages 40-69 (although not as high as households with children). Those aged 70-79 and 80+ then had significantly lower rates of licence and vehicle ownership, as you might expect as people age and become less able to drive. These patterns are fairly consistent with the census data scatter plot, except for the key parenting age bands of 30-39 and 40-49 where the census data analysis cannot calculate ownership per adult (just per person).

How has licence and motor vehicle ownership been changing for different age groups?

Across Australia, licence ownership has been increasing in recent years for older adults (particularly those over 70), and declining in those aged under 30 in states such as Victoria, New South Wales and Tasmania (for more detail see Update on Australian transport trends (December 2020)).

The following chart shows state-level changes in motor vehicle ownership and licence ownership between 2011 and 2016 by age bands: (note different scales on each axis)

This chart also shows something of a direct relationship between changes in motor vehicle and licence ownership, with people aged 70+ having the largest increases in both measures (except for Victorians aged 80+ who saw a decline in licence ownership). Younger age bands often had a decline in licence ownership, even if motor vehicle ownership in their households increased slightly (on average). For those aged in their 40s, there was generally an increase in licence ownership but only small changes in motor vehicle ownership – including slight declines in most states.

Teenagers in the ACT were an outlier, where there was a significant decline in licence ownership between 2011 and 2016 that someone with local knowledge might be able to explain.

Overall the relationship between changes licence ownership and changes in motor vehicle ownership is not super strong. Increasing licence ownership does not automatically translate into increasing motor vehicle ownership. There must be more factors at play.

I hope you’ve found this post interesting.

Appendix: What about households where census data is missing?

The non-response rate to the question about household motor vehicles was around 8.4% in 2016 (up from 6.5% in 2011) and most of these were for people who did not respond to the census at all. Non-response was fairly consistent across age groups as the next chart shows. Quite a few people had a response to the question about number of usual occupants, but did not respond to the question about motor vehicles. Poking around census data, these people often:

didn’t answer other questions;
were less likely to be in the labour force;
were generally on lower incomes;
were more likely to be renting;
were less likely to have a mortgage; and
were more likely to live in a flat, apartment or unit, and less likely to live in a standalone/separate house.

So my guess is that they were less likely to have high motor vehicle ownership.

The number of “not applicable” responses increased significantly into older age groups, and I expect most of these will be people in non-private dwellings (e.g. aged care). I have removed people with “not applicable” responses for usual occupants and household motor vehicles as they are likely to be non-private dwellings.

The chart gets a bit noisy for ages above 100 as very few such people live in private dwellings.

2 Comments | Australian Cities, Brisbane, Car ownership, drivers license, Melbourne, Mode share, Mode shift, Sydney | Tagged: Census Journey to Work, VISTA | Permalink
Posted by chrisloader

How and why does driver’s licence ownership vary across Sydney?

Sat 27 February, 2021

In a recent post I confirmed the link between driver’s licence ownership and public transport use at the individual level in Melbourne:

Unfortunately, spatial data around driver’s licence ownership is quite scarce in Australia, so not a lot is known about the spatial variations of licence ownership, nor what might explain them.

However, Transport for New South Wales do publish quarterly licensing statistics at the postcode level, and so this post takes a closer look at the patterns and possible demographic explanations of driver licence ownership across Sydney. I’ll also touch on the relationship between licence ownership and journey to work mode shares.

I have measured rates of licence ownership at the postcode level, and then compared these with other demographic factors that have shown to be significant in explaining variations in public transport mode shares in Melbourne (see my series on “Why are young adults more likely to use public transport”, parts 1, 2, and 3). These factors include socio-economic advantage and disadvantage, workplace location, age, recency of immigration, educational attainment, parenting status, motor vehicle ownership, population weighted density, proximity to high quality public transport, English proficiency, and student status.

I’m sorry it’s not a short post, but I have put some less profound analysis in appendices.

About the data

To calculate licence ownership rates you need counts of licences and population for geographic areas for the same point in time (or very close). Estimates of postcode population are only available from census data, so for most of the following analysis, I’ve combined 2016 “quarter 2” driver’s licence numbers (which includes learner permits) with (August) 2016 ABS census population counts. This is of course pre-COVID19, and patterns may (or may not) have changed since then.

I’ve mostly used population counts for persons aged 16-84. Obviously there are people over the age of 84 with licences, but I am attempting to discount people who may lose their eligibility to hold a licence due to aging.

I’ve also mapped postcodes to the Greater Sydney Greater Capital City Statistical Area boundary, and filtered for postcodes with a significant region within the Greater Sydney boundary (note that the boundaries do not perfectly align).

How does driver’s licence ownership vary across Sydney?

Here’s a map showing 2016 licence ownership rates for Sydney postcodes, with red signifying very high ownership, and green very low.

Technical note: For this map I have filtered to only show postcodes averaging at least 3 persons per hectare to focus on urban Sydney, but some excluded postcodes will be a mix of urban and non-urban land use so this is imperfect. Postcodes are not a great spatial geography for analysis as they vary significantly in size, but unfortunately that’s how the data is published (much easier for TNSW to extract I am sure).

The lowest licence ownership rates can be seen in and around the Sydney CBD, around major university campuses (especially UNSW/Randwick, Macquarie Park, University of Sydney/Camperdown), and at Silverwater (which includes a large Correctional Complex – inmates probably don’t renew their licence and would have a hard time gaining one!). There are also relatively low rates in some inner southern suburbs, in and near Parramatta, and near Sydney Airport.

Most outer urban postcodes have very high levels of licence ownership. One exception is postcode 2559 in the outer south-west, which contains a large public housing estate in the suburb of Claymore. More on that shortly.

Is there a relationship between licence ownership and journey to work transport mode share?

It will probably surprise no one that there was a relationship between driver’s licence ownership and private transport mode share of journeys to work. The following chart shows the average postcode mode share for the commuter population within specified bands of driver’s licence ownership.

I should point out that this a relationship, but not necessarily direct causality (either way). People might be more likely to get a driver’s licence because that is the only practical way to get work from where they live, and other people who do not want to – or cannot – get a driver’s licence may be able to choose to live and work in places that don’t require private transport to get to work.

And then there are some postcodes with pretty much saturated driver’s licence ownership but less than 60% private transport journey to work mode shares (top right). I’ll have more to say on these postcodes shortly.

The rest of this post will consider potential explanations for the spatial patterns of licence ownership, using demographic data for postcodes.

Socio-economic advantage and disadvantage

The following chart compares licence ownership with ABS’s Index of Socio-economic relative advantage and disadvantage (ISRAD, part of SE I FA), at the postcode level:

Near-saturated licence ownership was more common in the more advantaged postcodes, but lower rates of licence ownership were seen in postcodes in deciles 1, 7, and 8. Decile 1 stands to reason as areas of disadvantage (probably including many people unable to get a driver’s licence, eg due to disability), and the postcodes with very low licence ownership rates in deciles 7 and 8 contain or are adjacent to major university campuses.

However there are postcodes with licence ownership rates below 80 in all deciles – the relationship here is not super-strong and there are many exceptions to the pattern.

For people less familiar with the demographics of Sydney, here is a map showing 2016 ISRAD deciles for Sydney postcodes. Note that these deciles are calculated relative to the entire New South Wales population, and Sydney overall is more advantaged than the rest of the state, hence more green areas than red.

Workplace location

Workplace location is a known major driver of commuter mode share, with people working in the CBD much more likely to commute by public or active transport (see Why are younger adults more likely to use public transport? (an exploration of mode shares by age – part 2, plus analysis below). So how does it compare with licence ownership?

Here’s a scatter plot that shows that relationship. I’ve added socio-economic advantage and disadvantage colouring for further context, and labelled selected outlier and cloud-edge postcodes (unfortunately there is a slight bias against labelling postcodes containing many suburbs).

There is perhaps a weak relationship between work in Sydney CBD percentage and licence ownership, with postcodes containing larger shares of commuters going to the CBD (30%+) having lower licence ownership.

The chart also shows that disadvantaged postcodes generally had both fewer CBD commuters (as a proportion) and lower rates of licence ownership.

Commuter mode shares were much more strongly related to workplace location than licence ownership, as the following chart shows. Note that for this chart colour indicates licence ownership rate.

Within the main cloud, postcodes with lower rates of licence ownership (shades of orange) had slightly lower private transport mode shares and/or slightly lower percentage of commuters heading to the CBD. The upper outliers from the cloud include many wealthy postcodes that were not well connected to the CBD by the train network, while postcodes in the bottom-left of the cloud are on the train network.

To explore that further, here’s a similar chart, but with the data marks coloured by a relatively blunt measure: whether or not the postcode contained a train or busway station (based on point locations for stations, which is not perfect as some postcodes are very large and only part of the area might be within reach of a station, while other postcodes might have a station just outside the area):

Generally the postcodes with a train or busway station are towards the bottom-left of the cloud, and those without towards the top-right. I’ve labelled a few exceptions, which include university suburbs such as Macquarie Park, Kensington, Camperdown, and some larger postcodes where a station only serves a minority of the postcode area (eg 2027 and 2069).

The next chart plots commuter mode shares, licence ownership, and socio-economic advantage/disadvantage:

You can see a significant – but not tight – relationship between licence ownership and commuter mode share. Within the main cloud, disadvantaged postcodes are to the top-left, and the more advantaged postcodes to the bottom-right. That is, many disadvantaged postcodes had high private transport mode share despite lower licence ownership, and many more advantaged areas had lower private mode share despite higher licence ownership.

This suggests licence ownership was not the strongest driver of commuter mode choice, at least at the postcode level. Workplace location seems far more influential.

Many advantaged areas are closer to CBD(s) and often have higher quality public transport, walking, and cycling options. People in more advantaged areas are also more likely to work in well-paying jobs in the central city, where public transport is a more convenient and affordable mode. These people also probably face fewer barriers in obtaining a driver’s licence for when they do want to drive (eg access to a car).

While disadvantaged postcodes generally had lower rates of licence ownership, fewer people in these postcodes worked in the Sydney CBD, and they also tended to have high private transport commuter mode shares. I suspect this may be related to many lower income workplace locations being generally less accessible by public transport (particularly jobs in industrial areas). Any cost advantage of public transport is less likely to offset the relatively high convenience of private transport (not to suggest the design quality of public transport services is not important, and not to go into the issues of capital v operating cost of private transport).

However, I suspect public transport could be more competitive for travel from these disadvantaged low-licence-ownership areas to local schools and activity centres. I am aware of some disadvantaged areas of Melbourne that have highly productive bus routes, but not necessarily high public transport mode shares of journeys to work (particularly parts of Brimbank). These areas may be worth targeting for all-day public transport service upgrades, to contribute to both patronage growth and social inclusion objectives.

Just to round this out, here’s a very similar chart, but with Sydney CBD commuter percentage used for colour:

For most rates of licence ownership, there was a wide range of private transport mode shares and a wide range of Sydney CBD commuter percentages. There is a relationship between licence ownership and mode share, but it is not nearly as tight as the relationship between Sydney CBD commuter percentage and mode share.

Age

There’s obviously a relationship between age and licence ownership and NSW thankfully publishes detailed data on licence ownership by individual age. The following chart shows licence ownership by age, animated over time from 2005 to 2020.

Licence ownership peaks for ages around 35-70, and is lower for younger adults and tails off for the elderly as people become less capable of driving.

But there is a very curious dip in licence ownership around age 23-24, which became more pronounced after around 2008. Why might this be?

One hypothesis: People getting learner’s permits around age 18 but not progressing to a full licence and having their learner’s permit expire after 5 years – i.e. around age 22 or 23. I wonder whether people are getting a learner’s permit largely for proof of age purposes. NSW does have a specific Photo Card you can get for that, but the fee is $55 (or $5 at the time you get your driver’s licence), whereas a learner’s permit costs just $25 (and an Australia Post Keypass proof of age card costs $40). As of September 2020, there were 185,329 people aged 18-25 with a Photo Card, and 211,004 people aged 16-25 with a learner’s permit (unfortunately data isn’t available for perfectly aligning age ranges). Did something change about proof of age in 2008? I don’t live in Sydney but maybe locals could comment further on this?

However, I think I have uncovered a more likely explanation which I’ll discuss in the next section.

It would stand to reason that postcodes with more people in age ranges with lower licence ownership might have lower rates of licence ownership overall. I’ve calculated the ratio of the population aged 35-69 (roughly the peak licence-owning age range for 2016) to the population aged 15-84 (roughly the age range of most licence holders) for all postcodes to create the following chart:

You can see a very strong relationship between age make-up and licence ownership rates for postcodes (a linear regression gives an R-squared of 0.75). That is, the more the population skews to people aged 35-69, generally the higher the licence ownership rate.

Recent immigrants

My previous analysis found a strong relationship between public transport use and recency of immigration to Australia (see: Why were recent immigrants to Melbourne more likely to use public transport to get to work?). So does a similar relationship apply for licence ownership?

While I cannot directly match licence ownership and immigrant status at the individual level, I can compare these measures at the postcode level.

For the following chart I have classified postcodes by the percentage of residents who arrived between 2006 and 2016 – as at the 2016 census (my arbitrary definition of “recent immigrants” based on available data for this analysis), and compared that with licence ownership levels.

This chart shows a fairly strong relationship, and suggests more recent immigrants were less likely to have a driver’s licence – although the relationships is weaker for more disadvantaged postcodes (red/orange postcodes).

So why might recent immigrants be less likely to have a licence?

As we’ve already seen, some of these postcodes with low licence ownership are adjacent to universities, and no doubt included many international students who did not have a need for licence to get to study or work.
Many other skilled immigrants would work in the CBD(s), for which high quality public transport connections are generally available. In Melbourne, I found many recent immigrants live closer to the city where public transport is more plentiful, and many also live near train stations. Sydney is likely to be similar (more on that in a moment).
For some it might be because they cannot (yet) afford private transport (particularly immigrants on humanitarian visas) and/or that they don’t have sufficient English to get a learner’s permit (more on that later).
For some it might be that they are happy and attuned to using public transport, walking and/or cycling to get around, like they did in their country of origin. However when I analysed Melbourne commuter PT mode shares by immigrant country of origin, I didn’t find relationships I expected.
The age profile of immigrants skew towards younger adults, who for various reasons are less likely to own a driver’s licence.
I had wondered if some immigrants were driving using international licences instead, but NSW rules state that you can only drive on an international licence for up to three months, so that’s unlikely to explain the pattern.

Here’s a chart showing that immigrants skew towards young adults. The chart shows the New South Wales 2011 population for each calculated approximate age of immigrants when they arrived in Australia (= age + arrival year – 2011) (the best data I have available at present):

The most common ages at arrival were around 23-25 years. Sound familiar? It is also the age where driver’s licence ownership rates dip in New South Wales. I reckon there’s a good chance the influx of immigrants of this age may explain the dip in licence ownership rates for people in their early 20s.

My recent Melbourne research found recent immigrants were also less likely to own a motor vehicle. This evidence suggests low rates of driver’s licence ownership is also strongly related to the relatively high use of public transport by recent immigrants.

For reference, here’s a map showing the percentage of residents in 2016 who had moved to Australia between 2006 and 2016. If you know a little about the urban geography of Sydney, you’ll see higher concentrations around the CBDs, university campuses, and along some major train lines.

Parenting status

We know parents are less likely to use public transport (at least in Melbourne, but probably in all Australian cities), so are they also more likely to own a driver’s licence? The following data compares licencing and parenting rates (defined as proportion of adults doing unpaid caring work for their own children aged under 15) for postcodes:

There is a significant relationship, with postcodes with higher rates of parenting generally have higher rates of driver’s licence ownership. This may well be related to licence ownership rates also peaking for people of the most common parenting ages, and also the fact many young families live in the outer suburbs (where private transport is often more competitive than public transport). The postcodes with the lowest licence ownership rates also have very low proportions of parents (and probably contain many young adults who are studying).

For reference here is a map of parenting percentages for Sydney postcodes:

Motor vehicle ownership

It stands to reason that areas with higher driver’s licence ownership rates might also have higher motor vehicle ownership rates. I’ve calculated the ratio of persons aged 18-84 to household motor vehicles for each postcode, to create the following chart:

You can see the relationship is very strong, with more advantaged (and often near-CBD) postcodes towards the top of the cloud, and more disadvantaged postcodes mostly at the bottom and middle of the cloud.

Silverwater is an outlier – but I should point out that my calculation of motor vehicle ownership only counts people living in private dwellings while licence ownership is for all residents (including the many who resided in Silverwater’s correctional facilities).

There are also a small curious bunch of outliers with around 100 motor vehicles per 100 persons aged 18-84 but only 70-90 licences per 100 persons aged 16-84. These include urban fringe suburbs such as Marsden Park, Riverstone, Oakville, Rossmore, Gregory Hills, Leppington, Voyager Point, Kemps Creek, and Horsley Park. Perhaps these areas may contain farm vehicles that might skew the motor vehicle ownership rates.

While spatial data about licence ownership is unfortunately not readily available for most states of Australia, this chart suggested that motor vehicle ownership (something thankfully still captured by the census, despite ABS trying to drop the question) is a reasonably strong proxy for licence ownership.

Population weighted density

Given postcodes can be quite large (one has a population of over 100,000!), I prefer to use population-weighted density as a metric of urban density (as opposed to raw density). Here’s how that related to licence ownership (note a log scale on the X-axis):

That’s a pretty strong relationship, and of course not unexpected. Areas with higher population density generally have great public transport services, and more services and jobs would likely be accessible by walking, reducing the need for a car or driver’s licence.

Proximity to high quality public transport

I’ve previously confirmed a relationship between public transport mode share and proximity to high quality public transport, so does the presence of high quality public transport also relate to driver’s licence ownership?

As mentioned above, I’ve classified postcodes as to whether or not there was a train or busway station contained within the postcode boundary in 2016. It’s a blunt measure because stations may only serve a small part of large postcodes, or there may be a station just outside a postcode’s boundary that still provides good rail access to that postcode. Some postcodes were also served by light rail and/or very high frequency bus services, just not a train or busway station. I’d love to be able to look at licence ownership by distance from stations, but licensing data is unfortunately only available for postcodes, which does not provide enough resolution.

You can see postcodes with a station generally have lower rates of licence ownership than those without, but there is still plenty of variance across postcodes.

The green postcodes in the top of the left column include Camperdown (University of Sydney, close to the CBD with very high frequency on-road buses), Ultimo (just next to Central Station and the CBD), Kensington (includes UNSW campus, with strong bus (and now light rail) connections), Chippendale / Darlington (wedged between Central and Redfern Stations), and Waterloo / Zetland (very close to Green Square Station and also served by high frequency on-road buses).

Many of the postcodes with stations but high licence ownership (bottom of right hand column) are in the outer suburbs, where train frequencies may be lower, and public transport services in non-radial directions may have lower quality.

So the exceptions to the relationship are quite explainable, and I’d suggest there is a strong relationship. Again, it may be people without a licence choosing to live near public transport, and/or people not near high quality public transport deciding they must have a licence to get around.

Educational qualifications

I have also found a relationship between educational qualifications and commuter mode shares in Melbourne, so are licencing rates related to levels of educational attainment in Sydney?

There’s not much of a relationship happening here between licence ownership and education, other than some inner city postcodes with a high proportion of educated residents and lower rates of licence ownership. There is of course an (expected) relationship between advantage and education.

But just on that, one curious outlier postcode on the chart is Lakemba / Wiley Park (2195), with 29% of the population having a Bachelor’s degree or higher, but it being in the most disadvantaged decile. This postcode has a large proportion of people not born in Australia, with significant numbers born in Lebanon and Bangladesh. Perhaps this reasonably well-educated but highly disadvantaged population is a product of lack of recognition of overseas qualifications, and/or maybe issues with discrimination.

Distance from Sydney CBD

In Melbourne, distance from the CBD has a strong relationship with mode choice, and I would not be surprised if there was similarly a relationship with licence ownership. However Melbourne only has one large dense employment cluster (the central city), while Sydney has multiple large dense employment clusters which is likely to lead to different patterns (see Suburban employment clusters and the journey to work in Australian cities).

From the first map in this post you cannot see a strong relationship between licence ownership and distance from the Sydney CBD – it is clear that many other factors are influencing licence ownership rates across Sydney (such as proximity to university campuses and employment clusters). Having said that, it seems clear that most “outer” suburban postcodes have high levels of licence ownership, but distance from the CBD is probably not a good proxy for “outer”.

Also some postcodes are quite large, and are a little problematic to assign to a distance value or range from the CBD, and the presence of two large harbours means crow-flies distance to the Sydney CBD is not necessarily reflective of ease/speed of travel to the Sydney CBD.

For these reasons I’ve not crunched data on home distance from the Sydney CBD. With a lot more effort, perhaps a metric could be created that considers travel time to Sydney’s major centres (although these centres vary in size).

Which factors have the strongest relationship with licence ownership?

The factors shown above had the strongest relationships with licence ownership (I tested three other factors which had weaker relationships, covered in the appendices below).

I put all the factors for Greater Sydney postcodes into a simple linear multiple regression model, and without labouring the details, I found that the following factors were significant at explaining postcode licence ownership rates (each with p-values less than 0.05 and overall an R-squared of 0.83), listed with the most significant first:

Ratio of population aged 35-69 : population aged 15-84. For every 1% this ratio is higher, licence ownership per 100 persons aged 16-84 is generally 1.0 higher (all other things being equal)
Rate of motor vehicle ownership: every extra motor vehicle per 100 persons aged 18-84, there are generally 0.35 more licences per 100 persons aged 16-84 (all other things being equal)
People who have a bachelors degree or higher: For every 1% this is higher, licence ownership per 100 persons aged 16-84 is generally 0.18 higher (all other things being equal)
Postcodes containing or adjacent to a major university campus or correctional centre. These postcodes generally had 14 fewer licences per 100 persons aged 18-64 (all other things being equal)

Factors that fell out of the regression as not significant were Sydney CBD commuter percentage, presence of a train or busway station, socio-economic advantage/disadvantage, population weighted density, parenting percentage, student status, and percent of population speaking English very well. Of course many of these metrics would correlate with the four significant factors above.

I was a little surprised to see educational qualifications show up as significant, given the weak direct relationship seen in the scatter plot, however the impact was small (0.18) and it may be acting as a proxy for other factors such as proportion of commuters working in the Sydney CBD (which was the “strongest” factor that fell out – having a p-value of 0.11).

This analysis was done using postcode level which has issues in terms of blending populations. It is possible to look at individuals using household travel survey data, and I’ve had a quick look using VISTA data from Melbourne. Without going into full detail in this post, I’ve found stronger relationships with age, sex, household income, parenting status, main activity, distance from train stations, and a weaker relationship with distance from CBD. Maybe that could be the focus of a future post.

I hope you’ve found this interesting.

Appendix 1: English proficiency

Probably related to recent immigrant figures, postcodes with a larger proportion of residents speaking English very well generally had slightly higher levels of licence ownership, although the relationship is not tight:

Curiously though, the relationship seems to be stronger for more advantaged postcodes. Disadvantaged postcodes with lower levels of English proficiency still had licence ownership rates of around 80 per 100 persons aged 16-84 (top-left of the cloud).

As an aside: is English proficiency lower in postcodes with many recent immigrants?

The answer is yes, but lower levels of English proficiency are not always explained by recent immigration. Of course some of the recent immigrants will speak English very well (many settling in places like Manly, Darlinghurst, Waterloo, Pyrmont), while others will not, depending on their country of origin. The large red dot to the bottom-left is postcode 2166, which includes the migrant area of Cabramatta (sorry about the label that overlaps other data points). It would appear that this postcode has many longer term residents who don’t speak English very well (although they might rank themselves as speaking English “well” rather than “very well”, which is below my arbitrary threshold of “very well” plus native English speakers).

Appendix 2: Student status

I have recently found a relationship between student-status and and journey to work mode shares in Melbourne (although yet to be published at the time of writing). So does the proportion of residents (over 15) who are studying have a relationship with driver licence ownership rates?

Here’s a scatter plot, with socio-economic advantage and disadvantage overlaid:

Apart from some exceptional postcodes with larger proportions of students, there appears to be little to no relationship between studying and licence ownership.

1 Comment | Car ownership, drivers license, Migration, Mode share, Sydney, Urban density | Tagged: Census Journey to Work, population-weighted density, SEIFA | Permalink
Posted by chrisloader

Why were recent immigrants to Melbourne more likely to use public transport to get to work?

Mon 7 December, 2020

I’ve recently been analysing how public transport mode share varies with age and associated demographic factors. In part 3 of that series, I found that immigrants – and particularly recent immigrants – were much more likely to use public transport (PT) in their journey to work. This post explores why that might be, using data for Melbourne from the ABS Census (mostly 2016).

About immigrant data

The census covers both temporary and permanent residents. I’ve counted all people who were born overseas and came to Australia intending to stay for at least one year as “immigrants”, regardless of whether they were temporary or permanent residents.

It’s worth looking at the number of immigrants living in Greater Melbourne by age and arrival year, as at 2016:

Except for the first and last columns, each column represents 10 arrival years. You can see a significantly larger population of immigrants who arrived between 2006 and 2015, and they skewed significantly to ages 20-39. We know from previous analysis that younger adults are more likely to use public transport, so age is likely to play a role.

But how many immigrants are temporary residents? The census doesn’t include a question about permanent residency, but it is possible to track arrival year range cohorts over time.

The following chart tracks the number of immigrants for arrival year ranges between the 2006, 2011 and 2016 censuses (using Significant Urban Area geography).

If there were a significant number of temporary residents (although still intending to stay at least one year), then you’d see a large drop in the population of people who arrived 1996 to 2005 over time between 2006 and 2011/2016. There certainly was a drop off, but it was a small proportion.

This suggests most migrants end up being long-term residents (including many who enter on temporary visas but then gain permanent residency).

Numbers in all arrival year ranges dropped slowly over time through people leaving Melbourne (and possibly Australia) and deaths (particularly for immigrants from earlier years many of whom would be in their senior years).

Immigrants and public transport mode share of journeys work

To recap my previous analysis, the relationship between immigration year and PT mode share has held for the last three censuses (2006, 2011, and 2016), regardless of parenting status, birth year, or whether the someone worked inside or outside the City of Melbourne (local government area):

So why might recent immigrants be more likely to use public transport? From looking at the data, I think there are several plausible explanations.

To start with, they were more likely to work in the City of Melbourne, and we know journeys to work in the City of Melbourne have much higher public transport mode shares:

They were also more likely to live in areas with lower levels of motor vehicle ownership. Each column in the following chart represents the population of immigrants for a range of arrival years, and that population is coloured based on the motor vehicle ownership rate of all residents in the (SA1) areas in which they live (including non-immigrants). Note: immigrants themselves may have had different rates of motor vehicle ownership to the average of people in the areas in which they lived.

As I’ve mentioned previously, I do not have access to data to calculate the ratio of household motor vehicles to driving-aged adults within immigrant households, but I can calculate the ratio of household vehicles to all household residents (not all of whom may be of driving age).

The following chart shows that more recent immigrants were likely to have much lower levels of motor vehicle ownership that those who have been living in Australia longer.

Aside: Immigrants who arrived in Australia 1900-1945 had much higher rates of motor vehicle ownership than people born in Australia, but they were also all aged over 70 in 2016.

BUT if you look at PT mode shares for each vehicle : person ratio, there is still a relationship with year of arrival (see next chart), so car ownership doesn’t fully explain why recent immigrants were more likely to use public transport.

Looking at other factors, recent immigrants were slightly more likely to live closer to the city centre:

And they were more likely to live near a train station:

However not all recent immigrants to Melbourne lived near the city or a train station. Here’s a map showing the density of persons who arrived in Australia between 2006 and 2016 as at the August 2016 census.

There were significant concentrations in outer growth areas such Point Cook, Tarneit, and Craigieburn. These suburbs also happen to have very well patronised rail feeder bus routes, and unusually higher concentrations of central city commuters for their distance from the CBD.

Recent immigrants were more likely to live in areas of higher residential density:

And they were more likely to work near the city centre:

More-recent immigrants were also more likely to have a higher level of educational attainment than less-recent immigrants, and generally much higher than those born in Australia:

This probably reflects skilled immigration programs favouring people with higher educational qualifications. Indeed 60% of workers who arrived between January 2016 and the August 2016 census had a Bachelor or higher qualification. And we know from a previous post that highly qualified workers were more likely to work in central Melbourne, and were more likely to have used public transport in their journey to work.

Not only were more recent immigrants generally highly educated, many came to Melbourne to study to raise their educational attainment. Here is a chart showing the proportion of immigrants who were full-time or part-time students, by arrival year groups:

I will explore the relationship between student status and journey to work mode shares in an upcoming post.

How did immigrants shift around Melbourne over time?

Could internal migration explain why immigrants shifted away from public transport over time? Using census data across 2006, 2011, and 2016, it is possible to roughly track the population distribution of particular immigrant cohorts (although it’s not perfect because these immigrants may have moved in/out of Melbourne or left Australia between censuses, including temporary residents).

The following map shows the density of immigrants who arrived in Australia between 1996 and 2005 across census years 2006, 2011, and 2016:

In 2006 there were concentrations around the central city and many rail stations. But these concentrations reduced over time, with many of these people moving into other suburbs by 2011 or 2016 (or leaving Melbourne). In particular, many moved to outer suburbs such as Tarneit, Truganina, Point Cook, Derrimut, Craigieburn, Roxburgh Park, and Narre Warren South.

To help summarise these shifts, the following chart shows the distribution of this cohort across census years by distance from train stations, distance from the Melbourne CBD, and the motor vehicle ownership rate of the areas in which they lived:

You can see that they generally moved further away from train stations, further away from the CBD, and into areas that had higher levels of motor vehicle ownership. All these shifts are associated with reduced public transport mode share, and I suspect this pattern would not be unique to those who arrived 1996-2005.

Is there a relationship between PT mode shares and where people were born?

Firstly, here’s a chart showing the birth regions of Melbourne workers who were born outside Australia, by year of immigration (mostly 5 year bands). I’ve used ABS’s country of birth groups, except that I’ve separated North America from the other Americas.

The early half of the 20th century saw significant immigration from Europe, whereas in more recent times this has shifted to Asia, with southern and central Asia now the biggest source of immigrants. (Southern and central Asia includes India, Sri Lanka, Bangladesh, many former Soviet republics south of Russia and all “-stan” countries.)

So do journey to work public transport mode shares vary by immigrants’ region of birth?

There certainly is some variance between birth regions, but not quite what I was expecting. Immigrants from seemingly car-dominated north America had much higher PT mode shares than those born in European countries with reputations for higher quality public transport.

Of course people born in different parts of the world may be more or less likely to work in the City of Melbourne, and might be more or less likely to be parents. These factors strongly influence PT mode shares. So the next chart disaggregates the data by parenting status and work location (note a different X-axis scale used for each work location division).

This birth regions in this chart have the same ordering as the previous chart, but in most quadrants the mode shares are no longer in order (the top-right quadrant being the exception: non-parenting, working outside the City of Melbourne). Southern and central Asia tops PT mode shares for the other three quadrants, and by quite a large margin for City of Melbourne workers.

We know year of arrival into Australia is a significant factor in PT mode shares, and relative composition of immigrants has certainly changed over time. Also, age itself is likely to be a factor. The next chart adds these two dimensions. However, I have had to remove people working in the City of Melbourne, those under 20 and those over 60 – because the population for these categories became too small, introducing meaningless noise.

You can see there was a relationship between year of arrival and PT mode share within each age band, for both parenting and non-parenting workers. Central and Southern America generated the highest average PT mode shares while North Africa and the Middle East often had the lowest PT mode shares.

Here’s another look at that data, but comparing mode shares primarily by age rather than year of arrival. For this chart I’ve (also) removed parenting workers, and those who arrived before 1982, because they are mostly spread across just two 10 year age bands which isn’t really enough to show an age-based trend:

This chart shows that there was certainly a relationship between age and PT mode share for most birth regions (as well as year of arrival), at least for non-parents working outside the City of Melbourne.

I cannot be certain that this pattern also existed for all birth-regions for parenting workers and people who worked within the City of Melbourne, but I have previously shown a relationship between age and PT mode share for these categories (when ignoring birth region), so a relationship is likely.

So even with a changing mix of immigrant sources over time, age (or some other age-related factor) remains a significant factor when it comes to explaining public transport mode shares.

I hope you’ve found this at least half as interesting as I did.

Leave a Comment » | Car ownership, Melbourne, Migration, Mode share, Mode shift, Urban density | Tagged: Census Journey to Work | Permalink
Posted by chrisloader

Why are young adults more likely to use public transport? (an exploration of mode shares by age – part 3)

Wed 18 November, 2020

I’ve been exploring data to explain why younger adults are more likely to use public transport (PT) than older adults in Melbourne. This third post in a series looks at the relationship between public transport mode share and parenthood, the year in which people were born, whether people were born in Australia or overseas, and how recently immigrants arrived in Australia.

I’m using VISTA household travel survey data (all travel) and ABS Census data (journey to work only). For more detail about the data, see the first post in the series.

Parenthood

Are younger adults more likely to use public transport because they don’t (yet) have dependent children?

Consistent with previous analysis on this blog, there is a relationship between PT mode share and whether people are parents within family households. Here’s the data for general travel from VISTA 2012-18:

Parents were much less likely to use public transport than non-parents of the same age, with mums between 35 and 55 having a lower mode share (on average) than dads in the same age range.

The census tells us whether a worker did unpaid child care for a child of their own in the two weeks prior to the census, which I am using to distinguish parents and non-parents.

The following chart shows the proportion of working men and women who were parents, animated over censuses 2006 to 2016.

Parenting peaked around age 40 for male and female workers, and the proportion of workers who were parenting went up between 2006 and 2016.

So how do public transport mode shares vary by age if we separate out parents and non-parents? The following chart answers this, and also separates workers by whether or not they worked in the City of Melbourne local government area (a known major factor influencing mode shares), animating results over 2006, 2011, and 2016:

Note there is a different Y-axis scale for City of Melbourne and elsewhere.

There are a few really interesting take-aways here:

Parenting workers mostly had lower public transport mode shares than non-parenting workers of the same age, except for:
- dads over 30 who worked in the City of Melbourne,
- mums in their early 30s who worked in the City of Melbourne in 2016, and
- mums and dads in their 50s who worked outside the City of Melbourne (who had low PT mode shares around 4-5%, similar to non-parenting workers of the same age)
Public transport mode shares increased over time for almost all age bands, work locations, and for parenting and non-parenting workers.
Public transport mode shares for journeys to work in the City of Melbourne mostly declined with increasing age between 20 and 50, regardless of parenting responsibilities. Other age-related factors must be at play.
For people who worked outside the City of Melbourne, the mode share profile across age changed significantly over time for young adults. In 2006 there was a steady decline with age, but in 2011 PT mode shares were generally flat for those in their 20s, and in 2016 PT mode shares peaked for women in their late 20s (and also had a quite new pattern for dads in their 20s).
For parenting workers who work outside the City of Melbourne there was actually a slightly higher PT mode share for those over the age of 50. Parents over 50 might have older children who are more independent and therefore less reliant on their parents for transport. This might make it easier for the parents to use public transport. However this trend did not hold for dads in 2016.
PT mode shares for non-parenting women increased slightly beyond age 55 for all work locations. This will include women who were never parents, as well mums with non-dependent children so might again reflect a small return to public transport once children become independent. It may also be influenced by discounted PT “Seniors” fares available to people over 60 who are not working 35+ hours per week.

Lower public transport mode shares for parents is not surprising – they may be more time-poor and need more transport flexibility to link trips – eg dropping kids at childcare on the way to work can be more difficult with public transport (although it doesn’t seem to impact men travelling to the city centre nearly as much as women – I suspect because women are more likely to be working part time and doing childcare drop-offs and pick-ups). Parents may decide that time saving and convenience moving children is more important to them than lower transport costs from using PT.

However, addition of parenting responsibilities does not fully explain why public transport mode share generally declined with increasing age, particularly for non-parenting workers.

But I’m curious about the changing profile of mode share by age over time. Could it be influenced by…

Birth year / generations

Does public transport mode share vary by age and/or does it vary by when people were born, with different mode choices by different generations? To answer this I’m going to look at mode shares by both age and birth year.

For this analysis, I want to compare mode shares of birth year cohorts over time. The exact composition of these cohorts will change over time as there are deaths, new immigrants, and people who move overseas. I can only easily control for immigrants using census data – so for this section of my analysis I’m going to remove people not born in Australia (I will return to look at mode shares of immigrants shortly). Of course some people born in Australia who worked in Melbourne in 2016 may have spent a significant time living outside Australia before a census so this isn’t perfect.

Firstly, here’s a chart of journey to work PT mode shares by age, work location, and parenting status across 2006, 2011, and 2016 for people born in Australia:

Technical note: I’ve excluded data points where there was a small number of commuters, or a small number of public transport journeys where calculations are impacted by ABS randomisation to protect privacy.

You can see the general shape of the census year curves are similar within each quadrant (with a little noise at the extremes of age probably due to smaller volumes), suggesting a similar relationship between PT mode share and age holds over time.

We can clearly see how mode shares have increased over time for age bands, including:

those who work in the City of Melbourne (top row),
non-parenting younger adults who worked outside the City of Melbourne (bottom-left), and
to a smaller extent parents in their 30s and 40s who worked outside the City of Melbourne (bottom-right).

There were PT mode share spikes at age band 16-17 (at least for people working outside the City of Melbourne), which is just before people can gain independent licences. Those aged 18-19 working outside the City of Melbourne had a much lower PT mode share than those aged 16-17, and PT mode shares were lower again for those aged 15 who are perhaps more likely to work locally or be driven to work by parents.

So is this a general mode shift over time, or is it something intrinsic to birth years or “generations”? The next chart is similar to the previous, but the X-axis is notional birth year (approximated by census year – age at census time, which will be within a year of actual birth years).

Technical notes: For this chart I’ve calculated the 2 year birth year bands so that the youngest birth band is for ages 15-16 in all census years.

Let’s walk through the quadrants:

Non-parenting, City of Melbourne (top-left): PT mode shares have increased over time for those born between the 1940s and mid-1980s, despite these commuters getting older (assuming the same people still work within the City of Melbourne). This suggests general mode shift to PT over time has been stronger than any mode shift away from PT due to aging.
Parenting, City of Melbourne (top-right): PT mode shares have increased over time for almost all birth years, despite getting older (although the membership of this cohort will change as people acquire and lose parenting responsibilities). This is the same as non-parenting workers in the City of Melbourne.
Non-parenting, outside City of Melbourne (bottom-left): Ignoring those aged 15-22, mode shifts are generally smaller and not all in the same direction. If there was a negative relationships between age and PT mode share, you’d expect to see a shift away from PT between 2006 and 2016 for all cohorts. But for those born between around 1975 and 1985 (younger generation X and older millennials) and those born between 1940 and 1958 (mostly Baby Boomers) there was a small shift towards PT over time, despite them getting older. However these mode shifts were in the order of only 1-2%. Those born between 1960 and 1974 (mostly Gen X) shifted away from PT over time.
Parenting, outside City of Melbourne (bottom-right): For people born between around 1955 and 1980 (baby boomers and gen X) there was a shift towards PT between census years 2011 and 2016, despite people ageing. However in this quadrant mode shares were pretty flat and low over most ages (except at the young and old extremes of the cohort).

Of course many people will move from the left column to the right column as they start families, and then perhaps back to left column when they have adult children who no longer need care, so this analysis isn’t perfect.

So are there generational effects on PT mode share? Between 2006 and 2016 there was a significant shift towards PT in Melbourne for most birth years, parenting statuses and work locations, with only non-parenting workers born between 1960 and 1974 and working outside the City of Melbourne shifting away from PT. So the answer is no – any impact from birth year appears to be very small, and was generally swamped by an overall mode shift towards public transport.

That analysis was for for people born in Australia, but what about immigrants?

Immigrants to Australia

Are people who immigrated into Australia more recently, more likely to use PT to get to work? The next chart provides a clear “yes” answer to that question. I’ve included parenting status and work location as known significant factors, and animated the chart over censuses 2006, 2011 and 2016.

While the lines appear to shift left, they are really shifting up or down (people’s birth year doesn’t change), and are growing on the left with new younger workers entering the labour market, and falling away on the right as people leave the workforce.

Time of immigration had a big impact on PT mode shares – with people who arrived in Australia in the five years before a census most likely to use PT to get to work. The biggest difference in PT mode shares was for recent non-parenting immigrants working outside the City of Melbourne (bottom-left quadrant). Perhaps if public transport quality was boosted in areas with many recent immigrants there might be less loss of mode share over time. Or the drop in mode share might reflect people moving to areas with lower quality public transport.

For those working outside the City of Melbourne, PT mode share quickly fell after arrival into Australia, and after around 20 years living in Australia immigrant’s mode shares are similar to those who have been in Australia longer (or were born in Australia).

The chart also shows that there are age-related factors at play (beyond parenting and work location), regardless of whether people were born in Australia or immigrated – although much less so if they are parenting.

So could it be that recent immigrants make up a greater share of young adults, and might this explain the overall average mode shares across age groups?

The next chart shows the distribution of working population in five-year age bands by year of immigration / those born in Australia. I’ve animated this over 2006 to 2016. While the chart appears to animate with vertical movements, people actually shift one column to the right between census years.

If you watch the chart you’ll see that the immigrant share of the working population under 45 years increased between 2006 and 2016, with strong surges in immigration after 2006. This will undoubtedly impact the overall mode share for younger adults, but it doesn’t explain all of the mode share variance by age. The previous chart showed age-related factors influencing PT mode shares, regardless of when people moved to Australia.

I will explore potential reasons why recent immigrants were more likely to use public transport to get to work in an upcoming post.

Can we now explain why young adults are more likely to use public transport?

So far we’ve established that the following factors appear to have a strong impact on public transport mode shares:

Workplace distance from the CBD
Recency of immigration to Australia
Parenting status
Age

If the first three of these factors are the most important, and age or other age-related factors were not important, then we would expect flat mode shares across ages when you control for the other three factors.

The following matrix-of-worms chart combines all four factors. But please note that the Y axis within each row has a different scale and doesn’t necessarily start at zero. I am really looking at the slope of the line within each matrix cell, so I’m not too concerned about the actual values. I’ve only shown data points that included at least 400 commuters, and I’ve removed some columns and rows where data was too sparse to show meaningful trends.

How to make sense of this chart? Well, if the factors of parenting, arrival year and work distance from the CBD explained all the differences between age groups, then you would expect these lines to be flat within each matrix cell.

On the parenting (right) side of the chart, many of the worm lines are indeed quite flat, with the exception of those who arrived between 2006 and 2015 and those who worked within 2 km of the Melbourne CBD. Even though many of these matrix cells only have two or three data points, most data points include thousands of commuters so I don’t expect much false “noise” in the chart.

Within non-parenting commuters:

There is generally either a relationship with age, or a very low and flat PT mode share across ages, suggesting age itself, or some other age-related factors were at play.
The relationship with age appears to be strongest for more recent immigrants. The Born in Australia column also shows a strong relationship with age but this also has the widest age range. The columns for those who arrived between 1976 and 1995 only contain 3 to 5 age bands (all 30+), which will partly explain why there is less of an evident slope in the line.
Age band 60-69 is often an outlier to the trend, particularly for those born in Australia or who arrived between 1976 and 1985, again perhaps related to discounted “Seniors” public transport fares.

So I haven’t been able to fully explain variations in PT use by age. Age itself may be a factor, there may be other age-relevant factors that are important, or more likely there are lots of complex interactions between factors that are hard to unpick.

The next post in this series will look at the impact of income, socio-economic advantage/disadvantage, and occupation on PT mode shares across ages.

Leave a Comment » | Melbourne, Migration, Mode share | Tagged: Census Journey to Work, VISTA | Permalink
Posted by chrisloader

Charting Transport

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