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 »