Some people love them, others hate them. Personally, I think they are useful to maximise the lot yield of terrain dependant sites, but when used to attempt to create private roads and spaces with no regard to the form of the land, Cul-de-Sacs become pretty tiring. (If you can’t access the NY Times article, there’s a pdf of it here.
Highly popular after World War II, the cul-de-sac is essentially a dead-end residential street, often but not always ending with a large circular patch of pavement allowing vehicles to turn around. The form was initially embraced as something that promoted security, neighbourliness and efficient transportation…
Homeowners found that the cul-de-sac limited traffic, creating a sense of privacy, while encouraging ties among neighbours, who could hardly avoid one another. Developers liked the cul-de-sac because it made it possible to build on land unsuited to a grid street pattern and because home buyers were willing to pay a premium to live on one…
…while people within a cul-de-sac may know one another well, they are less likely to know people who live on other streets. “What was lost is a sense of community,” [Michael Lykoudis, dean of the School of Architecture at the University of Notre Dame] said.
What I dislike more than Cul-de-Sacs are Turning Heads, a geometric marvel permitting a three-point-turn to be executed at the end of a street. Developers can stick one of these in and save pavement compared to a Cul-de-Sac. But what they save in bitumen, they lose in functionality. A traditional Cul-de-Sac allows vehicles to turn about without stopping or reversing, generally an 8m radius will allow for a passenger vehicle to complete this manoeuvre in one go. For an industrial subdivision, radii up to 12m or more should be considered to facilitate rigid trucks or even semi trailers.
But don’t try to convert a Cul-de-Sac or two into a through road, unless you are prepared for a fight. In one American city (Eagan) all Cul-de-Sacs are sign posted with “Future Through Road”, just so residents can’t complain that they didn’t know!
Setting guidelines on the use and abuse of Cul-de-Sacs is probably an important exercise for local governments. Here in Australia, most councils have fairly well documented Development Control Plans that include such standards as the number of intersections and the distance from all lots in a residential subdivision to the nearest collector road, and the maximum length of a Cul-de-Sac when used. It makes it easier to know what can be done, but it also creates definite loopholes that developers will find ways to exploit.
At some point I’ll post an article on the vertical grading of Cul-de-Sac heads for different conditions – One for the civil engineers and road designers.