Cul-de-sac

A dead end, also known as a cul-de-sac (, from French for 'bag-bottom'), no through road or no exit road, is a street with only one inlet or outlet.

The term "dead end" is understood in all varieties of English, but the official terminology and traffic signs include many different alternatives. Some of these are used only regionally. In the United States and other countries, ''cul-de-sac'' is often not an exact synonym for ''dead end'' and refers to dead ends with a circular end, allowing for easy turning at the end of the road. In Australia and Canada, they are usually referred to as a ''court'' when they have a bulbous end.

Dead ends are added to road layouts in urban planning to limit through-traffic in residential areas. While some dead ends provide no possible passage except in and out of their road entry, others allow cyclists, pedestrians or other non-automotive traffic to pass through connecting easements or paths, an example of filtered permeability. The International Federation of Pedestrians proposed to call such streets "living end streets" and to provide signage at the entry of the streets that make this permeability for pedestrians and cyclists clear. Its application retains the dead end's primary function as a non-through road, but establishes complete pedestrian and bicycle network connectivity.

History

The earliest examples of dead ends were unearthed in the El Lahun workers' village in Egypt, which was built circa 1885 BC. The village is laid out with straight streets that intersect at right angles, akin to a grid but irregular. The western part of the excavated village, where the workers lived, shows fifteen narrow and short dead-ends laid out perpendicularly on either side of a wider, straight street; all terminate at the enclosing walls.

Dead-end streets also appeared during the classical period of Athens and Rome. The 15th century architect and planner Leon Battista Alberti implies in his writings that dead-end streets may have been used intentionally in antiquity for defense purposes. He writes:

The same opinion is expressed by an earlier thinker, Aristotle, when he criticized the Hippodamian grid:

In the UK, their prior existence is implied by the Public Health Act 1875 which banned their use in new developments.

Inferential evidence of their earlier use can also be drawn from the text of a German architect, Rudolf Eberstadt, that explains their purpose and utility:

It was in the United Kingdom that the cul-de-sac street type was first legislated into use, with the Hampstead Garden Suburb Act 1906. The proponents of the Act, Raymond Unwin and Barry Parker, thus gained permission to introduce culs-de-sac in their subsequent site plans, and they promoted it as a suitable street type for Garden Suburbs. Unwin's applications of the cul-de-sac and the related crescent always included pedestrian paths independent of the road network. This design feature reflects the predominance of pedestrian movement for local trips at the turn of the 20th century, and presages the current planning priority for increased pedestrian accessibility. The 1906 Act defined the nature of the cul-de-sac as a non-through road and restricted its length to . Garden cities in the UK that followed Hampstead, such as Welwyn Garden City, all included culs-de-sac.

In the 1920s, the garden city movement became more popular in the United States and, with it, came its design elements, such as the cul-de-sac. Clarence Stein, a main proponent of the movement, incorporated it in the Radburn, New Jersey subdivision, which was to become a model for subsequent neighborhood developments. The country's Federal Housing Authority (FHA) recommended and promoted their use through their 1936 guidelines and the power of lending development funds.

In Canada, a variation of Stein's Radburn 1929 plan that used crescents (loops) instead of culs-de-sac was built in 1947: Wildwood Park, Winnipeg, designed by Hubert Bird. In 1954, the Central Mortgage and Housing Corporation published its own guidelines in which the cul-de-sac was strongly recommended for local streets and, as the FHA in the US, used its lending power to see its inclusion in development plans. The Varsity Village and Braeside, subdivisions in Calgary, Alberta also used the Radburn model in the late 1960s.

In the 1960s the cul-de-sac attained systematic international application in planned new cities such as Doxiadis' Islamabad (1960). In the UK, new towns such as Harlow (1947) by Sir Frederick Gibberd and Milton Keynes (1967) incorporated culs-de-sac and crescents in their layouts.

Planning theorists have suggested the use of alternatives to culs-de-sac. Most notably, Christopher Alexander et al., in his 1977 book " A Pattern Language" (pattern #49) suggests the use of looped local roads which do not abruptly stop. Although dead end streets (culs-de-sac), would fit his definition of looped local roads Alexander suggestions that "cul-de-sacs ic are very bad from a social standpoint—they force interaction and they feel claustrophobic, because there is only one entrance". Doxiadis has additionally argued their important role in separating man from machine.

Originally-unplanned dead ends

Originally-unplanned dead ends have been added in city centers that are laid out on a grid by blocking through-traffic. Whole neighbourhood street reconfigurations emerged in several cities, mainly concentrated in North America and the UK, which include Berkeley, California; Seattle, Washington; and Vancouver, British Columbia. The transformation of grid plans since the 1970s limits access to an existing road that is newly designated as a major artery, enabling traffic to move smoothly on it, alleviating residents' concerns.

This selective, sporadic transformation is continuing. As traffic volumes increase and as cities decide to remove or reduce traffic on specific streets of central areas, streets are closed off using bollards or landscaping thus making new, originally unplanned dead ends and producing a new, functional blend of the inherited grid with newer street types. A recent variation of limiting traffic is managed closure by using retractable bollards that are activated only by designated card-holders.

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, the 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 customers. In Canada, a similar incentive was provided to developers by CMHC. The incentives, which were discontinued in the 1970s, gave the initial impetus for the application of the hierarchical pattern. In other countries, such incentives do not exist, and adoption is motivated by customer preferences.

American urban planning, in the 19th and the early 20th centuries, emphasized a grid plan, partly out of extensive reliance on foot, horse and trams 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 that 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 and 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.

The 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 those 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

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