Dead-end street
A dead end, also known as a cul-de-sac, a no outlet road, a no-through road or a no-exit road, is a street with only one combined inlet and outlet.
Dead ends are added to roads in urban planning designs to limit traffic in residential areas. Some dead ends prohibit all-through traffic, while others allow cyclists, pedestrians, or other non-automotive traffic to pass through connecting easements or paths. The latter case is an example of filtered permeability.
The International Federation of Pedestrians proposed calling such streets "living end streets" and to provide signage at the entry of the streets that clearly indicates non-automotive permeability. This would retain the dead end's primary function as a non-through road, but establish complete pedestrian and bicycle network connectivity.
"Dead end" is not the most commonly used expression in all English-speaking regions. Official terminology and traffic signs include many alternatives; some are only used regionally. In the UK, a dead end residential street is sometimes called a close. In the United States, a cul-de-sac is often not an exact synonym for "dead end,” as it refers explicitly to a dead-end street with a circular end, making it easier for vehicles to turn around. Street names are determined at the city or county level, with most choosing to use court for a bulbous cul-de-sac. In Australia, a street with a bulbous end is usually referred to as a court. In Canada, where street names are decided on the municipal level, culs-de-sac are usually named courts.
History
The earliest examples of dead ends were unearthed in the El Lahun workers' village in Egypt, which was built in 1885 BC. The village was planned and built orthogonally with straight streets that intersect at right angles in an irregular grid. The western section of the excavated village, once home to the workers, featured fifteen narrow, short dead ends arranged perpendicularly on either side of a wider, straight street and ending at the enclosing walls.Dead end streets also appeared during the classical periods 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:
The same opinion is expressed by Aristotle when he criticized the Hippodamian grid:
Inferential evidence of their earlier use can also be drawn from the writings of German architect Rudolf Eberstadt, which that explains the purpose of dead-end streets:
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 Hampstead Garden Suburb Act 1906 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 first modern cul-de-sac in America might be found in Buffalo, New York.
The country's Federal Housing Authority 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 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. 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. In the UK, new towns such as Harlow by Sir Frederick Gibberd and Milton Keynes 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" suggests the use of looped local roads which do not abruptly stop. Although dead end streets would fit his definition of looped local roads, Alexander suggestions that "cul-de-sacs 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 has been continuing into the 21st century. City planners sometimes, 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. As such, these actions make new, originally unplanned dead ends and producing a new, functional blend of the inherited grid with newer street types. A common variation of limiting traffic is managed via closure of 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 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 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, which are now heated by electricity, piped natural gas or oil.
Effects on local traffic
The use of culs-de-sac has been shown to reduce the volume of car traffic on residential streets within a subdivision which in turn can reduce noise, air pollution, and the probability of accidents.Ben-Joseph, and Lovegrove and Sayed, indicate a substantially lower collision rate for street networks based on the cul-de-sac street type. Dumbaugh and Rae 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. This study recommends hybrid street networks with dense concentrations of T-intersections, and concludes that a return to the 19th century gridiron is undesirable.
In turn, the decrease in traffic 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 neighborhood. 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.
File:Culs-de-sac Varisto, Vantaa.jpg|thumb|right|Cul-de-sac in Vantaa, Finland
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. The 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.
The 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 and Village Homes in Davis, California, they can increase active modes of mobility among their residents.