Do density and public transport resolve congestion?

(First Published January 2013)

The compact city/transit answer to the urban sustainability question

Expensive – and usually loss-making – public transit is enjoying a resurgence in the face of uncertainty over the supply and price of oil, concerns about the proliferation of private vehicles and greenhouse gas emissions, and  questions over the sustainability of our cities.

Transit is generally promoted as part of a programme to increase city densities.  In Auckland, for example, the plan is to recreate a compact city in order to get people out of cars.  A commitment to increasing the capacity of rail-based public transport is intended to support residential densities and justify concentrating public investment in the CBD.

I have addressed some of the issues this raises in earlier blogs.   (E.g., Rethink the Link, Five More Reasons, Thin Edge of the Tunnel Wedge, Derailing Auckland)

Exploring the relationship – the data

Using the Tom Tom international congestion index it is possible to explore the association between congestion and city density.  I analysed Q2/2012 morning congestion figures for 25 North American and 51 European cities covered by the index.  The index is based on the real time experience of drivers in areas of high usage of Tom Tom car navigation systems.  Congestion is measured as the deviation in travel time on individual routes at peak times compared with when they are flowing freely (generally at night).  The higher the deviation, the greater the congestion.

I looked for relationships between morning peak hour congestion and city size, population, and density using the Demographia July 2012 compendium of world urban areas data.   

Here are some summary figures for the second quarter, 2012:

Source: Tom Tom, 2012; Demographia, 2012 Congestion is additional peak hour travel time compared with free flow travel over the same routes.   (Out of interest, the comparable density figures for Auckland, Hamilton, Wellington and Christchurch are 2,400. 2,200, 1,900, and 2,000 respectively). 



Note the greater range of congestion figures among European compared with North American cities, and their significantly higher high and median figures.
 
The North American evidence:  higher density = more congestion?
I undertook simple and multiple regressions in each case to establish how far differences in congestion depend on the physical size of cities, how far on their populations, and how far on residential densities.
 

Among the North American cities only population density was statistically significant, explaining 52% of the differences in morning congestion among cities.  By and large, as densities increase, so does congestion (Figure 1).  The inference is that transport efficiency is no better among more compact cities, and may be worse.

Figure 1: The relationship between density and congestion, North American Cities

Does transit help?

It would take more comprehensive evaluation to establish how far transit systems might modify this relationship between density and congestion. The US News website provides a ranking of the top ten US transit systems based on ridership, safety, and government spending.  Only five are in the Tom Tom sample. 

Figure 2 orders the cities from worst to best performing on the ground of the difference between congestion that would be expected on density grounds alone (as predicted by the regression equation in Figure 1) and the actual congestion recorded.  Hence, Boston has higher levels of congestion (48%) than predicted (27%) on the basis of its density (just 800 persons per square km). And like poorly performing Seattle, it has one of the top ten transit systems as ranked by US News (4^th and 9^th respectively).  

Figure 2: Congestion performance, North American cities

The other poor performers based on this analysis include both high density Montreal, Ottawa, and Vancouver, and low density Atlanta. 

This is not a definitive analysis.  Rather, it suggests propositions for further consideration.  Among these, higher densities do not necessarily mean less congestion – more likely the opposite.  And leading edge transit does not necessarily fix the problem. 

The European Evidence: there is no evidence

The results for European cities were completely different, adding weight to the argument that context matters: what works in one setting will not necessarily work in another.  Across the 52 cities there is no relationship between density and congestion.  (There is, however, a weak relationship with cities’ physical size, r²=0.25). 

Figure 3 plots morning congestion as a deviation from the median for the 51 cities and includes a plot of densities.  It isn’t easy to read. In summary, the poor performers are Warsaw (density 3,100), Marseilles (1,300), Istanbul (9,700), Toulouse (1,100), Rome (3,400) and Brussels (2,600).  The better performers include the smaller cities of Malmo (density 3,600), Zagreb (5,700), Valencia (3,000), Seville (5,600) and Bern (2,300).

Figure 3: Congestion Performance, European cities

Does transit help?
A listing of the world’s top ten transit systems in 2011 included only four from the European sample (and only the New York subway from North America).  The London Underground comes in third, but London Metro Area comes in at a low 39^th on the European congestion rankings.  The Paris Metro is rated fifth , but Paris sits at 46^th among the 51 European cities for congestion.  The Berlin U-Bahn sits at 9^th place and the city's congestion 21^st in Europe.  Copenhagen is 10^th in the world transit stakes and 16^th in congestion ranking.

While the results are quite different from the North American analysis, the European evidence also offers no grounds for suggesting that density is a prerequisite either to better commuting conditions or that congestion reflects the quality of transit systems.

(A contrarian might argue, of course, that transit creates a commitment to a land use pattern that promotes congestion, delaying or distorting the decentralisation of employment that might otherwise occur in a well-connected city). 

Pursuing poorly performing precedents

If nothing else, the analysis raises issues which deserve much closer analysis, especially in Auckland where they do not support plans for a high cost transit system to support a compact city.

While planning – and planners – in Auckland have a tendency to cite overseas precedent to support expanded rail-based transit and higher residential densities, the variability of overseas experience suggests that this is a highly risky strategy.  Context really does matter – not only here but also among the precedent cities our planners love to cite. This is especially the case when poor performers on the congestion scale like Vancouver and Seattle in North America and London and Paris in Europe are touted as paragons of integrated land use and transport planning. 

So why do our planners and politicians continue to gamble the city's fiscal future on an economically flawed project which overseas data suggests has limited prospect of meeting its objectives?       

 

Being dense about dwellings: check the numbers!

Good news, bad news
In a previous posting I suggested that in New Zealand we are heading into the perfect housing storm. 

Now we have news that house prices and rentals are on the climb again, although stocks remain tight, as an annual inflation rate of 5.3% hits a 21 year high.  The economists are suggesting this is good news, although it means interest rates may have to be pushed up sooner than expected.

Well the bad news is that the housing crisis might just have worsened. 

Sure, its not an across-the-board crisis, but it is very real to large and important sections of our population.  Lack of housing affordability remains a threat to social sustainability and economic recovery.  So how are we responding to the threat -- or perhaps now the reality -- of a perfect housing storm?  What provisions are we making in our urban plans?

Smaller boxes – bigger footprint
Urban planners are still more preoccupied with fitting more dwellings into smaller areas than they are with responding to people's needs for housing.  It might help shift this fixation to point out that the preferred compact city solution is not only socially destructive, because it doesn't reflect need and does nothing for affordability, but it is also environmentally short-sighted.

Think about the metrics.

Take 100 people and house them at 1.5 residents per dwelling.  That’s arbitrary, but it reflects a widespread expectation that most new dwellings will house smaller households in central locations. 

In the interests of sustainability, let’s assume the resulting 67 dwellings are small, so that we can fit more of them onto less land.  Say, 120 sq meters per dwelling.  That totals 8,000 sq metres or thereabouts (more if we count the common areas in apartment buildings), 80 sq metres per person.  It’s also 67 kitchens, 67 lounges, maybe 67 media centres, at least 67 bathrooms, maybe some additional lighting for common areas and even some lifts.

Now take 100 people and fit them in at 3 people per dwelling, terraces, duplexes or fully detached houses.  Let’s make the dwellings bigger, say 200 sq metres.  We now need only 33 dwellings, 6,600 sq metres of dwelling, or 66 sq metres per person.  Less space per person, sure, but that's okay because now we need just half the kitchens, bathrooms, lounges and media centres.  However we look at it, we’ve used a lot less resources and have a spare 1,400 sq metres for open space, extra gardens, courtyards, whatever.  And with the capacity for extra bedrooms, we have much more flexible housing stock.

So which is the more sustainable?  Surely bigger dwellings with higher occupancies.  Surprised?

Can we plan for higher occupancies?
Now, we can’t engineer household size, can we?  Well, actually we already do.  With a housing shortfall we now require young adults to stay longer with their parents, force singles to move in with others,  require couples to take on boarders, or even promote multi-family living, all boosting occupancies.

So let’s at least understand that building more, smaller dwellings, especially medium- or high-rise apartments, does not necessarily deliver sustainable urban settlement, nor does it provide the flexibility to make the higher occupancy "solutions" we force on people easy to live with.

Larger dwellings do allow for diverse living arrangements, though; more multi-generational living, more non-family households, more sharing.  Like them or not, such arrangements are likely to increase, if only in response to the affordability issues we seem intent on entrenching.

So what’s happening to demand?
So why are planners trying to put more people into smaller dwellings anyway?  How relevant is the expectation that average household size will be smaller in the future than it has been in the past?

Most forecasts of housing “demand” simply extrapolate diminishing occupancy across demographic projections.  its all about the coefficients, and the assumption that household structures won’t change much in the medium to long-term. 

Well, it’s not that simple.

Things like an unexpected boom in the dissolution of relationships over the past three or four decades, the rapid growth in migration, and the recent stabilisation and even reversal in occupancy rates undermine the conceit that we can accurately forecast the structure, preferences, and behaviour of households 20 or 30 years hence.  If that's the case, why are our prescriptions for housing increasingly rigid?

Projecting household types
To understand this let’s stay with the current ”best”  projections of what households might look like in the future, and think about the implications for housing.

Statistics New Zealand (SNZ) medium projections to 2031 indicate that families with children will account for a minority of household growth in our main cities (see chart).  The figures may even shrink in Wellington and Christchurch.  According to this projection, they will make up 28% of new households in Auckland, though, so we could still need over 71,000 new dwellings for families there.  It’s reasonable to expect that detached housing will still work best for them.

Household Category Projections, Statistics New Zealand

Couples will account for more growth, though, maybe 36% of new households in Auckland according to SNZ, and singles for 32%.  So let's think about the preferences of the small household segment. 

So what will the small household segment look  like?
To get a feel for this, I divided the SNZ age projections into four (setting aside the main family age cohorts) : young adults (aged 20-29), empty nesters (the kids have left home, aged 50-64); early retirees (65-79), and later retirees (80+).  These are the groups most small households will come from.  But they have quite different housing preferences, so the nature of future demand for smaller dwellings depends on which ones grow the most.

Age-Based Housing Demand Segments (based on SNZ Projections)

So who will dominate growth?
Empty nesters and retirees will dominate the demand for new houses.  And these are not usually people who want to move into small, centralised apartments, at least not as a primary residence. 

Many of them have significant financial equity in their existing homes and emotional equity in their neighbourhoods.  If they move into smaller dwellings, they won’t be that small!  They will expect them to be well appointed and well located, probably close to where they already live. 

They won't want high or even medium rise.  And they are  likely to seek three or four bedrooms.  They will need the space to maintain active  lives into their seventies and eighties, more so than past generations.  They will be accommodating visiting family and friends; they will need offices, hobby areas, workshops, and storage. 

Here’s a model to take seriously if we are serious about sustainability

And as the baby boomers eventually become less independent, we might expect them to head into retirement villages, already a booming – and highly sustainable – form of housing.

In fact, we should look seriously at retirement villages if we want to understand the sorts of arrangements that could dominate new housing demand over the next 30 years.  Here, the market seems to have got it right. 

They offer varied living arrangements – detached and semi detached housing, terraces, apartments, and even on-site nursing facilities.  They offer medium density living with plenty of green space and gardens; common areas and shared facilities for recreation and leisure; plenty of on-site activity to cut down transport needs but also on-site parking to reflect the realities of modern living.  They achieve density and sustainability with style.  And – there must be a lesson here – they do it overwhelmingly in suburban if not city edge localities. 

So let's not assume that rising house prices mean a return to business as usual.  Far from it - freeing up the housing market must remain a top priority if the economy is in recovery mode.  And let's start looking to the suburbs  –and beyond  – for the housing solutions that might just help it stay that way.