What factors encourage public transport use?

Video: WestConnex: Greiner’s folly, Part 2: South-west: the problem & the solutions, EcoTransit

This post was inspired by the recent EcoTransit video posted above. In it, the claim is made that 90% of trips into the CBD from the South West are by public transport, while 90% of trips to South Sydney and the UNSW/Prince of Wales Hospital area are by car. No source was provided for these figures, although a 2008 government report entitled Employment and Commuting in Sydney’s Centres, 1996 – 2006 does provide data for Sydney as a whole and is the basis of this post.

Notes: Car journeys include both drivers and passengers. The majority of the balance of journeys were made by public transport, with walking and cycling generally not exceeding 5%-10%. All figures refer to journeys to work only and come from 2006 census data.

The data splits Sydney up into:

• 33 major “centres” (714,496 jobs or 37.1% of Sydney’s total)
• “no fixed address” (78,077 jobs or 4.1% of Sydney’s total)
• “unknown” (110,342 jobs or 5.7% of Sydney’s total)
• “remainder” (1,020,985 jobs or 53.1% of Sydney’s total)

As a general rule of thumb, the centres tend to have both a higher employment density plus a lower share of journeys to work made by car, and these two are negatively correlated (i.e. if one is higher, the other tends to be lower). At the top of the list is the Sydney CBD, with an employment density of 546.4 jobs/Ha and share of journeys by car of 19.5%. This compares to the figures for the non-centre areas of Sydney (“remainder”), with an employment density of 0.8 jobs/Ha and share of journeys by car of 85.2%.

Click to enlarge. (Source: Employment and Commuting in Sydney’s Centres, 1996 – 2006, Bureau of Transport Statistics, pages 2, 10)

There are some shortcomings of these data:

• They are relatively old (7 years). This means, for example, they pre-date the 2009 opening of the Epping to Chatswood Rail Link.
• They only include journeys to work (as this is the question asked on the census). Journeys to schools, universities, TAFE, etc are not included, even though they tend to occur at similar times as the morning commute, nor are journeys for recreation, shopping, etc.
• They don’t indicate what level of parking restrictions (for both on and off-street parking) have been put in place. Limiting the amount of available parking (particularly free and abundant parking) leads to a significant decrease in driving to work. The case of limited parking vs increased employment densities is a bit of a chicken and egg argument over which causes the other. It’s assumed here that they go hand in hand, and therefore employment density can be used as a proxy for parking limits.
• They don’t show which specific mode of transport was used (e.g. driver vs passenger or train vs bus vs walk). These figures are available in the original source document, but have been aggregated for simplicity.

Looking at the data in a more visual form, patterns become quickly evident. Here the mode share of trips by car is shown on the y-axis, the employment density is on the x-axis, and the size of each bubble indicates the size of each centre by employment. Bubbles are colour coded by centre type the same way as in the table above.

Click to enlarge. (Source: Employment and Commuting in Sydney’s Centres, 1996 – 2006, Bureau of Transport Statistics, pages 2, 10)

The link between employment density and driving to work is quite clear – the higher the employment density, the less likely workers are to drive to work. The correlation is strongest up to an employment density of around 150. Above this, higher employment densities do not seen to result in lower car usage, with the Sydney CBD (the large blue bubble on the far right), being a bit of an outlier. However, that is based on a fairly small sample size of 4 centres, whereas there are 29 centres under the 150 jobs/Ha threshold.

Proximity to the Sydney CBD also seems to result in lower car mode shares, evident by the non-CBD Sydney Central centres and the City Education/Health Precinct (the 3 blue and one green bubble on the bottom left) all having a lower car mode share than other centres with similar employment densities. Removing these 4 centres gives a much cleaner correlation, where going above the 150 jobs/Ha threshold still reduces car mode share, but at a lower rate.

Education precincts also have lower car mode shares. The City and Randwick Education/Health Precincts (the two green bubbles in the bottom left) both have lower car mode shares than other centres with similar employment densities. This is more pronounced for the former, given its proximity to the CBD, but can still be clearly seen for the latter.

Business parks, on the other hand, tend to have higher car mode shares. Norwest Business Park and Macquarie Park (the 2 red bubbles at the top), both have much higher car mode shares than other centres with similar employment densities. Olympic Park and Rhodes also have higher car mode shares than similar centres. This may suggest that it is their lack of good rail connections that encourage their workers to drive. The former 2 had no rail connections in 2006, while the latter 2 had only limited rail connections.

But support for this in the data is mixed, given that North Sydney and Chatswood (the two red bubbles on the right) both enjoy excellent rail connections, but still display a greater tendency for its workers to drive. In the case of North Sydney (the red bubble on the right), it has a much higher employment density than Surry Hills/Kings Cross (the lowest blue bubble on the left) does (369 jobs/Ha and 137 jobs/Ha respectively). Yet both have similar car mode shares (39.4% and 37.9% respectively) and are both in close proximity to the CBD. In addition, the Randwick Education/Health Precinct (the green bubble second from the bottom) has no rail connection and achieves a similar car mode share to St Leonards/Crows Nest (the red bubble third from the right) which does have a rail connection. This is despite the former having a lower employment density to the latter (70 jobs/Ha and 107 jobs/Ha respectively).

This suggests that the type of public transport available does not impact its mode share significantly. Instead, it’s the quality of that transport, things like speed and frequency, that determine its use. So somewhere like Rhodes, which has relatively infrequent and slow trains on the Northern Line, is not as well services as the Randwick Education/Health Precinct, with its frequent express buses that come in from Central and the CBD via bus only lanes.

Summary

Higher employment densities are correlated with lower car use in journeys to work, particularly for densities up to 150 jobs/Ha. Proximity of employment to the CBD enhances this correlation. Meanwhile, workers at universities are less likely to drive, while workers at business parks are more likely to drive. The availability of frequent and fast public transport encourages a modal shift to public transport, the mere existence of a rail connection does not.

Further Reading

Paul Mees’ 2010 book Transport for Suburbia discusses the issue of population density and whether a high population density is required to achieve high public transport usage. He argues that it is not, and that a low density city can still achieve high public transport usage.

Post Script: Paul Mees sadly passed away earlier this week on Wednesday, before this post was published, but after the above paragraph was written. He was a public transport advocate, heading the Melbourne based Public Transport Users Association for a decade, as well as an academic at both Melbourne University and RMIT.

Chris Loader at Charting Transport looked into this further for cities from various countries, then in more detail on Australian cities, and finally into great detail on just Sydney. Two maps looking at employment density and public transport use in Sydney most relevant to this from the final link are included below.

An earlier post on the WestConnex looked at whether it should link up to the CBD, and what sort of trips car travel is best suited to compared to what sort of trips public transport is best suited to.

Jobs density in Sydney. Click to enlarge. (Source: Charting Transport)

Public transport mode share by destination. Click to enlarge. (Source: Charting Transport)