The following question was recently posted on Quora:
“Are cul-de-sacs considered poor urban planning?”
Read the following responses from industry experts:
Isaac Gaetz, structural engineer:
Yes, Cul-de-sacs are generally considered poor urban planning by urban planners, however they are popular in suburban planning (if such a thing exists). Urban development, by definition, is about dense city living, it is not rural, nor is it SUB urban.
The thinking behind urban development is that higher density of living and business it will provide an opportunity for better living, better financial prosperity and the development will be better for the environment. Whether or not urban developments actually accomplishes any or all of these is a subject for another question, it is not specifically germane to this discussion. With that being said, the most fundamental characteristic of urban development is density. planning that promotes density is in general, good urban planning, and planning that reduces density is in general, poor urban planning.
Cul-de-sacs do not promote the same density as traditional grid planning provides. This is because cul-de-sacs create complex, car-centric traffic flows. If you are in a traditional grid neighborhood and want to head to different location, you can generally move directly towards your destination. In a cul-de-sac neighborhood, you will often be forced to take a very circuitous route, possible moving in the exact opposite direction of your final target. I’ve used the same map from Michael Lee‘s answer to illustrate my point. If you wanted to move from one of the houses I’ve drawn (little black squares) instead of moving generally towards the home, you have to take quite an elaborate and long path to actually get there:
Cul-de-sacs also do not promote mass transit forms that are complementary to walking. For example, it is difficult to design a bus system that weaves in and out of the various nooks and crannies of a cul-de-sac system. It is also difficult for passengers to understand and use such a system. As a result such systems do not generally exist at all, or if they do, they are inefficient and underutilized. These further increase the above described car dependency that defines cul-de-sacs.
Theoretically, and underground or overhead subway system can be immune to the irregularities of a cul-de-sac neighborhood, however the inherent lower density of cul-de-sac communities typically make such systems untenable.
Cul-de-sacs also lead to irregular shaped lots with triangles and other shapes which are difficult to develop properly, meaning fewer homes and business per acre/Sq Mile/Sq km. Here is an example, You can see the lots around the cul-de-sac are irregular shaped, in some cases they have long slender points, which are space that is not usable for building and not very functional for gardening or leisure either.
Michael Lee, public policy analyst:
Full disclosure: I am not an urban planner by profession. But I do find the discipline fascinating.
Yes and no. The answer really depends on the planner’s goals.
Cul-de-sacs are a bit troublesome because they interrupt a street grid, thereby shunting traffic to designated “main” roads. That’s not inherently a problem, but it increases (and concentrates) traffic on main roads, which often means those main roads are unsafe for pedestrians, cyclists, and other non-automotive users. If you’ve got two lanes of traffic each direction moving at 40 miles per hour, you’d be hard pressed to have cyclists safely using the road. Kids won’t be playing in the street, pedestrians probably won’t walk along those roads, retail corridors will stagnate, and the area will lose an “urban” feel. As I said, that’s not necessarily a problem unless you’re trying to design for a mixed-use, walkable area. (And those are quite popular).
Of course, cul-de-sacs are quite popular, too. They reduce traffic on residential streets, since the only people coming and going on a particular road are the residents. Parents love them because they provide a sense of security - five houses, for example, might be overlooking the cul-de-sac, meaning that any parent can keep an eye on his or her children quite easily, and won’t have to worry about kids wandering too far out of view.
Consider the following view of a part of my childhood hometown of Hanford, CA (population 50,000 or so last time I looked):
Contrast that easily-distributed traffic pattern with the following area of town, developed somewhat later:
Note that there are significantly fewer means to get from one end of the square mile to another, largely because planners chose to make this part of town much more explicitly residential. Commercial sectors are few and far between in this part of town, centered mostly at the south corners (10th and Fargo, 11th and Fargo). If you had gotten gas at 10th and Fargo, and needed to go visit a friend on Cinnamon Ave, there’s no way for you to get there without staying on the main roads. Thus traffic is concentrated on those roads, and I can assure you, they’re not populated by much pedestrian traffic. (This being California’s San Joaquin Valley, though, that’s not surprising).
Most urban planners place heavy emphasis on walkability, on “downtown” sectors, on getting people out of their cars. So from that perspective, cul-de-sacs are assuredly poorly planned. But they’re not going away too easily, not as long as single-family homes are popular, because people love them, and significant portions of the country have been built with them in mind. I’d be very interested in seeing ideas about how we can remake those areas with more mixed-use and walkability in mind.
Yousaf Shah, urban planning consultant:
I am a planner by training and profession, and many of the answers already provided are quite correct. Cul-de-sacs are a tool in residential development and whether or not they are good planning depends on the goals a particular planner/municipality is trying to achieve for the neighborhood. The key concern was actually safety. By making the streets dead end rather than continuous, it made specific neighborhoods and even blocks the spatial domain of the residents of the area. The meandering paths and dead ends not only slowed down traffic and kept people moving at slow speeds, it also deterred petty criminals who would have to have a very good understanding of the layout of the streets to beat local law enforcement in a getaway.
Cul-de-sacs which allow a pathway for pedestrians and bicycles to flow through but not cars can be a good urban planning tool.
Making neighbourhoods more permeable to pedestrians and bicycles than to cars increases the odds of people choosing to walk or ride instead of drive and increases the viability of community interconnectedness while preserving child-play safe streets.
Without trying too hard, I remember half-a-dozen pedestrian and cyclist permeable but car impermeable streets in Toronto, Singapore and Vancouver. I can think of pedestrian and cyclist cross-paths in Aurora Ontario, which is practically the definition of suburban as well.
Car-impermeable cul-de-sacs have economic advantages.
Cul-de-sacs, being disconnected, adapt better to topography. Since they carry no through traffic, they often have reduced standards for street widths, sidewalks and curbs. In Radburn, for example, the introduction of cul-de-sacs reduced street area and the length of utilities, such as water and sewer lines, by 25 percent as compared to a typical gridiron street plan. According to Stein, the cost savings on roads and utilities paid for the construction of open spaces and parks.
So while Isaac Gaetz‘s answer is accurate, it’s not the complete story. Variable permeability which leads to greater walking and riding is much to be desired, and is in keeping with Jane Jacob’s observations about shorter blocks.