CUL-DE-SAC: Urban Network Virus or Antidote?

Cul-de-sac is a French word ‘cul-de-sac[1] that literally means ‘the bottom of the sack’. In urban terminology, it commonly refers to a dead-end street.

Cul-de-sacs are ‘double edge swords’ in urban phenomena and that for both: networks of connective paths and social vitality and security. Traditional cul-de-sacs (figure 1) (Murati, B. 2018) were short with straight narrow streets with just a few houses on them and they were intended to provide a sort of public realm for residents: street where children can play without fear of fast moving traffic while allowing pedestrian as well as vehicular access to dwellings.

Figure 1. (Besnik Murati 2018) Traditional Cul-De-Sac [2]

However, with increased number of automobiles on the network they became wider and much longer with straight and curvilinear street forms and more dwellings on them (figure 2) (Murati, B. 2018). They are still quiet, have less accident rates than in gridiron pattern, lower burglary rates and so on, while on the other hand, their tree like patterns and dead-ends prohibits through movements that enforces traffic on the boundaries (figure 3) (Murati, B. 2018). As a result, they compromise network of connective paths, contributes congestions on peak hours and enforces neighbouring.

 

       Figure 2. (Besnik Murati 2018)             Figure 3. (Besnik Murati 2018)
     Modern-planned long Cul-De-Sacs [3]      Connected VS Tree Like urban street web [4]

Tree-like street patterns are the worst possible network structure; on the right side of the tree axis (figure 3) (Murati, B. 2018), every red dot has only one path in order to connect to any of the red dots in a layout, while on the left side of the tree axis, every blue dot has thousands of possibilities to connect with other blue-dots.

Nonetheless, there are some economic reasons (figure 3) (Murati, B. 2018) that fosters its continuous development through history: low infrastructure cost comparing to traditional interconnected and gridiron street patterns that requires ≈ 35% more road construction (Socio-economic Series 75, 2002) [5] i.e. less building area-less profit for developers, they adopt better on topography, housing real-estate values are higher than in gridiron structure and increases with the depth of plots-buildings, street design is less formal, provides low cost solution for utility infrastructure, and so on.

Figure 4. Economic incentives for cul-de-sac VS gridiron street network [6]

So, incentives for cul-de-sacs development and its structural pattern layouts are triggered upon different spatial, social and economic factors. As urban phenomena, they represent complex typology in street hierarchy upon their twofold character as scale dependent variables that plays significant role in network connectivity in one hand and in degree of vitality and crime on the other hand.

There are two different approaches and that upon two schools of thought that tries to describe social vitality and security indicators upon spatial relationship patterns of cul-de-sacs with urban form: Jane Jacobs’s (Jacobs, J. 1961) that stands against cul-de-sacs and advocates ‘streets with eyes’-connected streets that inhabits residents and strangers and both acts as ‘police’ and on the other hand, Oscar Newman’s [7] (Newman, O. 1972) school which advocates that streets with single use (pro cul-de-sacs) that doesn’t welcome strangers are healthier and safer because residents would easily identify and trace intruder movements and challenge them. However, their continuous presence in urban form structure suggests their controversial historic role and importance on constituting the spatial out of the social.

Contemplating intrinsic relationship between the social and the spatial (Hillier et.al.1976), urban form presumably embodies complexities of social organization patterns. Hierarchically, cul-de-sacs represents a small part of the greater intricacy. But understanding their socio-spatial correlation patterns is not possible upon the social alone because one variable is missing in the equation. Therefore, understanding the spatial is essential in order to determine their relationship.

UCL Space Syntax [8] methodology is being used to reveal cul-de-sac’s spatial patterns and role on network connectivity of Prishtina – Capital city of Kosovo. Investigation on evolution of cul-de-sacs structural patterns and its correlation with network connectivity, liveability and security indicators advocates for traditional patterns to modern ones; the latter compromises connectivity and security as they drop with the length.

To summarise, investigation on historic role of cul-de-sac’s in socio-spatial correlation encourages traditional configurations patterns, as antidote to planned arrays because their spatial structure delivers capability to maintain equilibrium of network connectivity with liveability and security.

 

References:

[1] https://www.merriam-webster.com/dictionary/cul-de-sac

[2] http://blog.horizonsgroup.org

[3] http://blog.horizonsgroup.org

[4] http://blog.horizonsgroup.org

[5] https://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/socio75.html

[6] http://blog.horizonsgroup.org

[7] https://www.huduser.gov/publications/pdf/def.pdf

[8] http://discovery.ucl.ac.uk/1415080/

Hillier, B.; Leaman, A; Stansall, P; Bedford, M. 1976 “Space syntax. Environment and Planning B: Planning and Design”, volume 3(2).

Jacobs, J. 1961. The Death and Life of Great American Cities. Reprint.2016. New York. Random House.