Cul-de-sac - Suburban Use and Benefits

Suburban Use and Benefits

Since the end of World War II, new subdivisions in the United States and Canada, as well as New Towns in England and other countries have made extensive use of the cul-de-sac and crescent (loops) street types. Typically, there is one or several central roads in the subdivision with many cul-de-sac streets of varying length, branching out from the main roads, to fill the land in the subdivision; a dendrite or hierarchical pattern. Since the 1960s, this pattern has been the dominant road network structure of suburbs and exurbs in the United States, Canada, and Australia. It is also increasingly popular in Latin America, Western Europe, and China. In this pattern, there are only a few roads (relative to the number of cul-de-sac streets) leading out of the subdivision and into other subdivisions or onto major roads.

In the US, these changes can be attributed to real-estate developers' desire to meet FHA guidelines and make federal home loans available to their consumers. In Canada a similar incentive was provided to developers by CMHC. These incentives, which were discontinued in the 70s, gave the initial impetus for the application of the hierarchical pattern. In other countries such incentives do not exist and its adoption is motivated by consumer preferences.

Nineteenth and early 20th century American urban planning, emphasized a grid plan, partly out of extensive reliance on foot, horse and streetcars for transportation. In such earlier urban development, alleys were included to allow for deliveries of soiled supplies, such as coal, to the rear of houses which are now heated by electricity, piped natural gas or oil.

The use of culs-de-sac reduces the amount of car traffic on residential streets within the subdivision, thus reducing noise, air pollution and the probability of accidents. Ben-Joseph (1995) and Lovegrove/Sayed (2006) indicate a substantially lower collision rate for street networks based on the cul-de-sac street type. Dumbaugh and Rae (2009) suggest that land use patterns play a significant role in traffic safety and should be considered in conjunction with the network pattern. While all intersection types in general increase the incidence of fatal crashes, four-way intersections, which rarely occur in a network with cul-de-sac or loop streets, increase total and injurious crashes significantly. The study recommends hybrid street networks with dense concentrations of T-intersections and concludes that a return to the 19th century gridiron is undesirable.

This decrease in traffic, in turn, is thought to lower the incidence of crime and increase desirability, because in most cases the people who traverse the cul-de-sac either live there or are guests of those who do. CPTED planning principles suggest increased natural surveillance and sense of ownership as a means of fostering security in a neighbourhood. Both of these phenomena occur naturally on a cul-de-sac street as does social networking. Design guidelines based on the CPTED perspective recommend its use for these reasons.

Cul-de-sac streets increase spontaneous outdoor activity by children. A study in California examined the amount of child play that occurred on the streets of neighbourhoods with different characteristics; grid pattern and culs-de-sac. The findings indicate that culs-de-sac showed substantial increase in play activity than the open grid street pattern. Culs-de-sac reduce perceived danger from traffic thereby encouraging more outdoor play.

Similar studies in Europe and Australia found that children’s outdoor play is significantly reduced on through roads where traffic is, or perceived by parents to be, a risk. In addition, they confirmed the results of the seminal Donald Appleyard 1982 study which showed the negative correlation between amount of traffic and social networks. This inverse correlation between amounts of traffic and sociability of streets was reconfirmed by a newer study that repeated Appleyard’s San Francisco analysis in Bristol, UK. It showed that the cul-de-sac street with the lowest traffic of the three streets had the highest level of social interaction. These studies recommend the use of the cul-de-sac or strong traffic calming measures. When culs-de-sac are interconnected with foot and bike paths, as for example in Vauban, Freiburg, Village Homes, Davis, California, they can increase active modes of mobility among their residents.

Real estate developers prefer culs-de-sac because they allow builders to fit more houses into oddly shaped tracts of land and facilitate building to the edges of rivers and property lines. They also choose these discontinuous network patterns of cul-de-sac and loop streets because of the often significant economies in infrastructure costs compared to the grid plan.

From an environmental perspective, culs-de-sac 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.

The desirability of the cul-de-sac street type among home buyers is implied by the evidence that they often pay up to a 20% premium for a home on such a street, according to one study. This could be because there is considerably less passing traffic, resulting in less noise and reduced actual or perceived risk, increasing the sense of tranquility. A survey of residents on three types of streets: cul-de-sac, loop, and through (grid) recorded their preferences among these types. It found that 82% of cul-de-sac residents preferred their own street type, 18% preferred a loop, and 0% the grid. Only 13% of grid street residents preferred their own type and 54% would choose a cul-de-sac to live on. Two other studies, reported in 1990 and 2009 respectively, confirmed this upward trend and determined the premium that cul-de-sac streets command. The first found a 29% premium over the streets in a grid. The second, focused on trails and greenbelts, found that other amenities including cul-de-sac streets add significantly to the home value.

The positive feelings that a cul-de-sac street could evoke, that residents value, are expressed vividly by Allan Jacobs in describing a short (250 ft), narrow (60 ft), and densely built (14 du/acre) cul-de-sac in the Shadyside neighborhood of Pittsburgh, Pennsylvania: “Step into Roslyn Place and you are likely to sense, immediately, that you are in a place, a special place, a handsome place, a safe place, a welcoming place, a place where you might wish to live.” ... “narrowness and enclosure and intimacy bring a feeling of safety to Roslyn Place... “Stay on our street” is all the kids have to know.”

Gated communities, steadily increasing worldwide, employ cul-de-sac and loop street networks because, having a dendrite structure, they reduce the number of through roads and, consequently, the corresponding number of entries and exits to be controlled.