THE ROLE OF URBAN PATTERNS IN THE PERFORMANCE OF CIRCULATION SYSTEMS
Journal Name:
- Orta Doğu Teknik Üniversitesi Mimarlık Fakültesi Dergisi
Keywords (Original Language):
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Abstract (2. Language):
Circulation network design, widely mentioned as road network design, is
one of the main topics in urban planning, urban transportation planning,
traffic engineering and urban design. In the literature on road network
design, problems and principles are examined through quantitative and
qualitative researches (Magnanti and Wong, 1984; Hillier, 1987; Ran and
Boyce, 1996; Hillier, 1999; Southworth and Ben-Joseph, 2003; Drezner
and Wesolowsky, 2003, Marshall, 2005). The former one implies analysis
and simulation of demographic and economic variables in order to apply
appropriate circulation schemes, while the latter one deals with various
factors of design and aims to create urban spaces regarding ‘space quality’.
This paper examines the role of urban patterns in the formation of road
networks; thereby depicting relative performance and handicaps of road
networks under stated travel distribution among specified units.
Road network design requires knowledge of circulation concepts and
methodology of assessment. This study provides a topological analysis
method and assessment criteria in order to understand performances of
various types of road networks. In order to constitute road networks,
circulation systems are adapted on three basic types of urban pattern:
the grid, the hexagon and the radio-centric. Finally, two certain travel
demand matrices are assigned to the specified road networks in order to
assess relative advantages of various patterns and circulation networks.
At the first stage, travel distribution among units (zones) is assumed to
be uniform while second stage is performed with a matrix representing
a centre-oriented travel distribution pattern. Here, circulation systems
connote to the conceptual representation of movement of vehicles on
specific routes, while circulation network (road network) is the concrete
form of any specificied circulation system.
There are numerous studies on advanced traffic management systems,
which mainly focus on the issue of uninterrupted traffic flow (Ran and
Boyce, 1996; Levinson, 2003). In the last decade, intelligent transportation
systems and traveler route guidance stystems are extensively adapted
to urban transportation systems. On the other hand, there are limited
studies measuring the the performances of such systems, which are highly
dependent to the characteristics of road network (Emmerink et al., 2003;
Levinson, 2003). Marshall (2005) argues that street pattern is significantly
influenced by the “geometry of movement” and “the topology of route
connectivity”. Geometry of movement is the representation of individuals’
travel patterns while connectivity refers to the structural (topological)
characteristics of road network; such as hierarchy and composition of links
(road sections) and nodes (junctions).
This study deals with the role of urban patterns on the formation of road
networks and relative performances of circulation systems. Conceptual
forms of circulation systems, described by Wright et al.(1989) are adapted
to basic types of urban patterns (the grid, the hexagonal and the radiocentric)
in order to obtain road networks. Those networks are compared in
terms of network efficiency, measured by average travel distance, traffic
volume/capacity ratio, standard deviation among travel volumes, and
average travel time. Proposed measures are applied to 33 test networks,
which are derived from three base patterns: the grid, the hexagon, and
the radio-centric. Traffic assignment procedure is carried out in order to
observe performances of road networks.Results showed that when uniform travel distribution is considered,
connected networks, such as convex polygons and concentric corridors,
perform better than less connected circulation networks. Those networks
perform with uniform volume capacity ratios; therefore, hierarchial
capacity design is not necessary for such systems. Convex systems have
high efficiency when adapted to grid patterns rather than hexagonal
and radio-centric. Average traffic volumes and standard deviation on
convex networks are much less than semi-connected or tree networks.
Hence, connected road networks perform with less average travel
distance and average travel time. Results showed that grid patterns are
more advantageous when convex circulation systems are adapted, while
hexagonal patterns perform better when tree or star shaped systems are
adapted.
Compared to two-way systems, one-way circulation systems prove to
be inefficient in terms of travel distance and time, however, conflicts at
intersections are much less. When centre-oriented trips are assigned to road
networks, star-shaped and tree-shaped networks perform better, however,
total travel time and total travel distance is more than others. Those
networks perform with moderate volume capacity ratios.
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Abstract (Original Language):
Ulaşım planlaması ve kentsel tasarım yazınında kentsel dokuların tasarımı,
oluşumu ve özellikleri konusunda yaygın çalışmalar bulunmasına rağmen,
yol ağlarının kentsel trafiğin işleyişi üzerindeki etkilerini inceleyen
az sayıda çalışma vardır (1). Bu çalışmada kentsel dokular ile ulaşım
sistemleri arasındaki ilişki irdelenmektedir. Bunun için kentsel tasarım
yazınında tanımlanmış bazı temel dokulardan yola çıkılarak kavramsal
yol ağları oluşturulmakta ve bu yol ağlarının öngörülen bazı yolculuk
istemleri altında nasıl işledikleri araştırılmaktadır. Tanımlanan yol ağları
ilingesel (topological) ve çizge-kuramsal (graph-theoretical) yöntemlerden
yararlanılarak sınıflandırılmıştır. Kavramsal düzeyde yapılan sorgulama
sonucunda yol ağlarının göreli üstünlükleri veya sorunları sıralanmaktadır.
Yolların işleyişindeki farklılaşmanın gerisinde dokuların ve yol ağlarının
ilingesel özelliklerinin etkili olduğu savlanmaktadır. Kentsel çevrenin,
özelde kentsel dokuların tasarlanması aşamasında doğrudan veya dolaylı
olarak dolaşım mekanları (yol ağı) da oluşturulmaktadır. Çalışmanın
sonucunda kentsel dokuların, farklı zamanlarda gerçekleşecek trafik
için yeterli olmaması veya gereğinden fazla yol mekanı sunulması gibi
sorunların aşılmasına yönelik değerlendirmeler yapılmaktadır.
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