Is “per passenger km” the right metric for comparing modes?

Animation of Tokyo from farmland to megalopolis - click and wait a second

It might seem intuitively obvious that any comparisons between cars and public transport should be on a “per kilometre” basis. After all, as Steven Smith at Market Urbanism points out, “people take trips of varying length, and longer trips are more expensive than shorter trips, so the desire to standardize and compare makes us want to simply divide the trips by their length and call it even”.

However here are four observers of the US transport and planning scene who all say the concept of comparing transport modes on a per mile basis (or more correctly, per passenger mile basis) is deeply flawed. Steven Smith says both supporters and opponents of light rail use per passenger mile costs and subsidies to justify their positions, but the problem is that the purpose of transit is not to travel long distances:

These are not pleasure travellers trying to get as far from home as possible, but rather commuters trying to get to wherever their jobs and schools are located. But the distance to this “somewhere” is not a variable to be held constant – it actually varies with population and job density, which is highly correlated with mode of transit. Places with train lines generally have and allow for denser development and thus less distance between your house and your workplace or school – the difference in average commute distance between urban and exurban areas could be as much as an order of magnitude.

Michael Lewin reckons per passenger mile comparisons are flawed because they assume that trips involve the same mileage on any mode. However in the real world our choice, he says, is not between a city with a 20 mile bus commute and one with a 20 mile car commute:

Rather, our choice is: do we want to make cities more compact, thus increasing the number of short commutes (some of which will typically involve transit, for the reasons stated above) or do we want to create a relatively spread-out city with lots of long commutes (most of which will usually be by car)?

In the compact city, fewer passenger-miles will be travelled, which means that all the negative externalities of travel (e.g. pollution, collisions, public costs) will be lower. And because people will be somewhat more likely to use transit and carpool, both cars and transit vehicles will be more fuel-efficient, because cars and buses are more fuel-efficient when they have more passengers. By contrast, in the car-oriented, spread-out city, both car and transit commutes will typically be longer, and both cars and buses will have fewer passengers.

Alon Levy at Pedestrian Observations is annoyed that subsidies for roads look much lower when they’re divided by the appropriate number of trillions and expressed in terms of passenger miles of travel. He says:

Passenger miles don’t vote. They’re not a unit of deservedness of subsidy. They’re one unit of transportation consumption. They’re like tons of staple as a unit of food production, or calories as a unit of consumption. We don’t subsidize food based on cents per calorie.

Even as a unit of consumption, there are flaws in passenger miles as a concept, when it comes to intermodal comparisons. The reason: at equal de facto mobility, transit riders travel shorter distances than drivers….. Transit is slower than driving on uncongested roads, but has higher capacity than any road. In addition, transit is at its best at high frequency, which requires high intensity of uses, whereas cars are the opposite. The result is that transit cities are denser than car cities – in other words, need less passenger miles.

Matt Yglesias at Think Progress reckons the concept of passenger miles is borderline incoherent and senselessly biased in favour of auto-oriented road projects:

The use of passenger miles as a unit of measures embeds the assumption that the goal of a regional intra-urban transportation system is to have people travelling as far as possible. Now you could imagine a city in which individuals, firms, structures, natural resources, etc. are just strewn about at random. If that was the case, then you probably would want to organize transportation to maximize distance travelled. People would have arbitrary transportation needs, might need to get very far away, etc. But when you’re talking about a real growing city, a focus on passenger miles just implies a focus on spreading your urban area out as widely as possible. Read the rest of this entry »


Would Seaside work in outer suburban Melbourne?

Click to take a "walk" around Seaside, Florida

When I first saw pictures of Seaside many years ago, I imagined that’s what the outer suburbs of Melbourne could look like one day. Click on the picture and go for a “walk” around the Florida village that had a key role in inspiring the New Urbanism movement. Seaside is famous – you might know it from its role in The Truman Show or from its distinctive array of “story book” houses.

Although the houses are detached, you’ll see many of the key ideas of New Urbanism in Seaside, including houses that open up to neighbourly streets and paths, have no garages and are within an easy walk of the town centre. Keep an eye out for walking paths. Given the kind of detached housing that’s being built today in Australian cities, I find it extraordinary that the first stage of Seaside was started 30 years ago!

It doesn’t push all the New Urbanism buttons. For example, the range of dwelling types is pretty limited and there’s not much evidence of transit orientation (it’s not a commuter village). Nevertheless, average density approaches the aspirational 25 dwellings per hectare, well in excess of the 15 dwellings per hectare promoted in Melbourne 2030 and in new fringe structure plans like the one for Toolern, near Melton.

For my money, the key reason Seaside has such broad popular appeal is the two and three storey detached “Hansel and Gretel” houses, with their faux widow’s walks and sometimes extravagant follies. Some architects however find it twee – they wince at the sentimentality and overwrought quaintness of the place.

I think it also appeals because of the determination of the architects to eliminate garages. This enables living areas to be placed at the front within a conversation’s distance of the sidewalk. It captures a half-forgotten notion of neighbourliness and conjures romantic images like promenading.

This contrasts with the practice in Melbourne where both new suburban houses and traditional inner city terraces tend to put bedrooms at the front and the main living areas at the rear (only apartments and older suburban houses seem to have living areas facing the street, although they’re usually set way back from the front boundary).

A parallel with Melbourne though is the limited area of private open space. I hear frequent condemnation of big houses with small yards in Melbourne’s outer suburbs (as if buyers can’t make their own decisions about what size yard they want!) but the area of private open space in Seaside looks positively miniscule. As with apartment dwellers, I’d expect the quality of the public realm is an important offset.

As a possible model for Australian suburbia, it’s important to get Seaside in context. It’s not a big place – it only covers about 50 32 hectares (the part of Fishermans Bend mooted for redevelopment is 200 Ha) and has around 500 houses. (Update: the whole area though, including very similar contiguous developments, is about 100 Ha with 1,000 or more houses – see Comments). Also, it’s essentially a beachside resort for people who are well-off. Many of the houses are rented to holiday makers and in that sense it functions more like the swank residential areas close to Hastings Street in Noosa than the suburbs of Melbourne or Sydney.

Like Noosa, it’s a long way from the nearest major urban centre. Dwellings are architect-designed and costly to build – properties at Seaside have sold for as much as $5 million (presumably ones on the beachfront). Further, I suspect a major reason there are so few cars in the streets is that holiday makers fly in and have no need to drive in what is essentially a self-contained resort. The town centre seems improbably built-up for 500 dwellings and that could be because this is a tourist town, drawing visitors from well beyond Seaside’s border.

I can imagine something like Seaside working on old brownfield sites in Melbourne like Fishermans Bend and E-Gate, but what would happen if it were transplanted to the suburban fringe? Read the rest of this entry »


Are cul-de-sacs a dead end?

Cul-de-sacs in the Medina District, Tunisia (Wikipedia)

The New Urbanism hates cul-de-sacs – they’re emblematic of much that’s wrong with car-oriented suburban cities, including poor walkability, low transit provision, long travel distances, “excessive” demand for privacy, and even low social capital.

I might be in a minority, but I’m an admirer of cul-de-sacs. They’ve been around for thousands of years for good reason. I grew up in what in my day was called a “dead end”, 6 km from the city centre. I lived in a terraced mews in Sydney for six years, just 1 km from the Town Hall. I now live in a seven property cul-de-sac developed in the 1950s, 8 km from Melbourne town hall.

The great advantage of cul-de-sacs is they have no through traffic, so they’re quieter and it’s safer for children to play outside on the street. As long as they’re not too long, they can create a sense of place and possibly promote greater social interaction among residents too (although it’s not clear how much of that’s due to the cul-de-sac form; to lower traffic levels; or in some cases to joint ownership of common property). It’s also a matter of no little importance that residents seem to like them.

Another claim is cul-de-sacs reduce infrastructure costs significantly compared to a grid plan. Further, they “allow greater flexibility than the common grid in adapting to the natural grades of a site and to its ecologically sensitive features, such as streams, creeks and mature forest growth”.

Cul-de-sacs are popularly associated with outer suburban developments and that’s why they get such a bad rap. However they can work in a range of urban contexts. They’ve often been used in inner city traffic calming schemes (where they’re called “street closures”). Large, higher density redevelopment projects like this one in Brisbane use what is essentially the cul-de-sac form to give access to dwellings without a street frontage. Yarra Bank Court in Abbotsford would be better with pedestrian access for residents at the far end but is otherwise a delightful “dead end”.

According to critics, the key disadvantage of suburban cul de sacs is they create a circuitous road system, necessitating longer travelling distances. This discourages walking and increases the cost of providing public transport when compared to a traditional grid pattern.

It’s true that many older suburban estates are relatively impermeable. However as inner city street closures show, it is quite easy to design cul-de-sacs that are open for pedestrians but not cars. It’s also quite simple to have a 1 or 1.5 km rectilinear grid of main roads for buses (e.g. see Toolern) with cul-de-sacs confined to “filling in” each square.

I think the main reason cul-de-sacs are demonised by new urbanists is because they’re conflated with the problems of outer suburban development. Consider this quote from Wesley Marshall, an assistant professor of civil engineering at the University of Colorado:

A lot of people feel that they want to live in a cul-de-sac, they feel like it’s a safer place to be. The reality is yes, you’re safer – if you never leave your cul-de-sac. But if you actually move around town like a normal person, your town as a whole is much more dangerous.

Professor Marshall says fatal accident rates are lower in areas with a traditional grid pattern, but he makes an elementary mistake. The traditional areas are older – they don’t have fewer fatal accidents because of their street morphology but  because they’re denser, with more mixed development, more traffic and slower travel speeds than outer suburban areas. The primary “culprit” here isn’t the cul-de-sac, it’s the lower density and monoculture of the newer suburbs.

The same article says “people who live in more sparse, tree-like communities drive about 18 percent more than people who live in dense grids”. Again, that’s primarily because of differences in density. For example, destinations are further apart in outer suburbs so residents are less likely to walk or cycle. Given the article refers to the US experience, it’s possible, even likely, that differences in income between the two areas are an important explanatory factor too. At least this time the writer talks about “sparse” communities rather than specifically fingering cul-de-sacs. Read the rest of this entry »


Why do inner city residents walk and tram to work?

More than half of all trips to work by residents of the inner city are made by walking, cycling or public transport. In fact three quarters as many residents walk and cycle as use public transport for their commute.

Why? Is it because of the higher density of the inner city?

Inner city Melbourne (photo by ExTester)

The view that density predicts more sustainable transport use is a common one. While it has some role, it is not the key force at play here. In fact there’s evidence that the population density of some parts of the inner city is not that much higher than that of the suburbs – this is because the average size of households in the inner city is relatively small compared to suburban locations.

There are also examples of higher density developments where use of public transport is quite low, for example edge cities in the US and suburban New Urbanism developments like Orenco in Portland, Oregon.

So if density isn’t the primary force driving more sustainable transport use in the inner city, what is?

Here are four plausible explanations.

The first is proximity. Inner city residents live cheek by jowl with the largest concentration of jobs in the metropolitan area – the inner city has 28% of all metropolitan Melbourne’s jobs and the CBD, despite its diminutive geographical size, has 14.5%. There is no other location in Melbourne that comes within cooee of the job density of the CBD. Read the rest of this entry »


Stop making sense!

David Byrne on bicycles, Atlanta’s sprawl and burying highways.

On New York: “If I had a magic wand — ahhh, that’s easy — I’d bury the highways, as they’ve done in some other cities. The West Side Highway and the FDR would both go underground, with parks on top that link the city and its people to their waterfront. Cafes, clubs and recreational stuff too. It would be glorious”.

David Byrne at Atlanta new urbanism conference (too late, it finishes today)

David Byrne’s book, Bicycle Diaries. He’s been riding his bike in New York since the 80s.

David Byrne on Paris’s bike sharing scheme

And David Byrne on Houston – land of the free


Are cul de sacs a curse?

One of the tenets of new urbanism is that streets should be laid out in a rectilinear grid to maximise connectivity i.e. to minimise public transport and walking distances.

This research project in Seattle seems to confirm the wisdom of that principle. It compared the distance travelled by residents of two neighbourhoods and found that in Woodinville, where the dominant street form is the cul de sac, residents travel 26% more kilometres than residents of Ballard, where streets are laid out in a rectilinear grid.

As it happens, I’ve spent a fair bit of my life living on a “no through road” or similar street form and I think the advantages of cul de sacs are too often neglected. I grew up in a closed street, lived for six years in a mews and currently live with my family in a short cul de sac created in the 1950s when a larger property was subdivided into seven lots.

The great advantage of the cul de sac is low traffic. When my children were very young my wife and I were relaxed about them playing in the street because the only cars that entered the street were residents or their visitors. And for that same reason we don’t have issues with traffic noise like we used to have in North Fitzroy.  These are major advantages and should not be dismissed lightly.

But cul de sacs have another advantage. If they’re not too long, they can create a sense of a place that is shared or “owned” by a small number of residents. We got to know all our neighbours well, shared child supervision responsibilities and even had an annual lunch in the middle of the road.  Read the rest of this entry »