grid&cul de sac
Transcript of grid&cul de sac
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Utilizing GIS to Measure Street Connectivity
and Pedestrian Accessibility
Comparing Cul-De-Sac and Grid Neighborhoods
in the Houston Metropolitan Area
GIS-Transportation Symposium
Chang Yi
Community & Regional Planning
University of Texas at Austin
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Presentation Outline
Background
Research Question Neighborhood Selections & Descriptions
Analysis Methods
Findings
Conclusions & Implications
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
What is Connectivity / Accessibility?
Street Connectivity
The Level of Inter-Connectedness of Streets
Pedestrian Accessibility The Level of Ease in reaching Spatially Separate
Opportunities (by walking) Travel Distance
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Why Connectivity and Accessibility?
New Urbanists
Cul-De-Sac (-)
Streets not Inter-Connected
Few Route Choices Long Dist.
Discourage Peds/Auto.Dependence Specialized Functions: Inefficient
Traffic Congestion in Major Roads
Grid (+)
Highly connected Streets
More Route Choices
Shorter Distances Easier for Pedestrian Travels
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Why not?
Developers/Homebuyers Grid (-)
Through traffics (Crane, 1996) Nuisance: Safety Hazards, Noise
Increase Infra. Cost
(holding all other things equal)
Decrease Affordability/Profitability
Cul-De-Sac (+)
No Through Traffics
Quiet / Private Residential Env.
Safer (for children) Market Preference toward Cul-De-Sac
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Grid Street converted to Cul-De-Sac, City of Berkeley
Source: Southworth and Ben-Joseph, 2004
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Alternative Street Design?
Creative Cul-De-Sacs ?
(Southworth and Ben-Joseph, 2004) Cul-De-Sacs integrated with Open Space and Local
Destinations on Ped-Friendly Environment
Cul-De-Sac Neighborhoods with High Street
Connectivity and Accessibility + Benefits of CDS
Not Streets, Pedestrian-Oriented Design Street Debate may have overlooked the Importance of
Neighborhood Design and misses Potentials of CDS
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Any Example of
Creatively Designed Cul-De-Sac?
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Source: Stein, 1966
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Source: Stein, 1966
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Radburn: Creatively Designed Cul-De-Sacs
Short & Straight Cul-De-Sacs
Auto-Oriented (separated from Pedestrians)
Private and Quiet Residential Environments
Benefits of Cul-De-Sacs
Connect Pedestrian Movement with Natural
Features and Local Destinations
Schools / Parks are Accessible for Pedestrians
Benefits of the Grid
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Research Question
Could the benefits New Urbansits try to achieve
with a grid street pattern be realized in a cul-de-sac
oriented neighborhood?
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Neighborhood Selection
The Radburn-Influenced Neighborhood
Grand Lakes, Katy
Pure Grid Street Neighborhood
Houston Heights, Houston Conventional Cul-De-Sac Neighborhood
The Panther Creek Village, The Woodlands
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
Case 1: Hybrid Cul-De-Sac
Grand Lakes
Radburn-Influenced Cul-De-Sac +
Pedestrian Trails
1,400 acre
Parks
Elementary Schools
Clear boundary
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Pedestrian Trail
Lake
Elementary School
Park
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
N i hb h d
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Case 2: Pure Grid
Houston Heights
Downtown Historic District
1,500 Acre
Schools, PocketParks, Community
Centers
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
B k d |R h Q i | N i hb h d | A l i M h d | Fi di | C l i li i
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Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
The Panther Creek
Village, the Woodlands
Ian McHarg
Ecological Planning
Conventional Cul-
De-Sacs
1,700 acre
Boundary defined by
Major Arterials
Case 3: Conventional Cul-De-Sacs
B k d |R h Q i | N i hb h d | An l i M th d | Fi di | C l i & I li i
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Background |Research Questions | Neighborhoods |Analysis Methods | Findings | Conclusions & Implications
Measuring Street Connectivity & Pedestrian Accessibility
Street Connectivity Indicators
Link Node Ratio
Percentage of Cul-De-Sacs
Percentage of 4 way Intersections
Street Density(Total Street Miles/Neighborhood Area)
Alpha Index / Gamma Index
Pedestrian Accessibility Indicators
Pedestrian Route Directness (PRD)
Pedestrian Catchment Area (PCA)TransCAD GIS
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Street Connectivity: Link Node Ratio
Internal Street Connectivity
intersections / intersections + cul-de-sacs
Three
routes
Link Node Ratio = 7/8 = 0.88
Only One Route from A to B
A
B
Three Routes from A to B
Link Node Ratio = 9/8 = 1.13
Source & Presentation Idea : Dill, 2004
Ratio = 7/8 = 0.88
A
B
Ratio = 7/8 = 0.88
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= Network Area/Aerial Area
(Always Smaller than 1)
Pedestrian Catchment Area
(PCA)
A Quarter Mile Network Buffer
A Quarter Mile Aerial Buffer
P d i R Di
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a1 a2 a3
a4
a5
PARK
Pedestrian Route Directness
(Without Ped Trail)
Aerial Distancea1+a2+a3+a4+a5++aN = A
b1 b2 b3
b4b5
PARK
Shortest Network Distance
b1+b2+b3+b4+b5++bN = B
PRD for Park = Net/Aerial Dist.
=B/A (>1)
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a1 a2 a3
a4
a5
PARK
Pedestrian Route Directness
(with Pedestrian Trail)
Aerial Distancea1+a2+a3+a4+a5++aN = A
PARK
c1 c2 c3
c4
c5
Shortest Network Distance
c1+c2+c3+c4+c5++cN = C
PRD for Park = Net/Aerial Dist.
=C/A (>1)
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How to Measure Street Connectivity?
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Digitizing Neighborhood Map
Di i i i i hb h d M
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Digitizing Neighborhood Map
Di i i i N i hb h d M
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Digitizing Neighborhood Map
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Street ConnectivityGrand
Lakes
No Trails
Grand Lakes
With Trails
Panther
Creek
Village
Houston
Heights
Street Pattern ConventionalCul-De-Sacs
HybridCul-De-Sacs
Cul-De-Sacs
Grid
Link Node Ratio1.11 1.38 1.10 1.65
Percentage of Cul-De-Sacs 0.39 0.14
0.41 0.03
Percentage of 4
Way Intersections 0.06 0.100.08
0.82
Street Density
(Miles/Area) 16.00 22.23 17.32 22.72
Alpha Index
0.06 0.19 0.05 0.33Gamma Index
0.37 0.46 0.37 0.55
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Street ConnectivityGrand
Lakes
No Trails
Grand Lakes
With Trails
Panther
Creek
Village
Houston
Heights
Street Pattern ConventionalCul-De-Sacs
HybridCul-De-Sacs
Cul-De-Sacs
Grid
Link Node Ratio1.11 1.38 1.10 1.65
Percentage of Cul-De-Sacs 0.39 0.14
0.41 0.03
Percentage of 4
Way Intersections 0.06 0.100.08
0.82
Street Density
(Miles/Area) 16.00 22.23 17.32 22.72
Alpha Index
0.06 0.19 0.05 0.33Gamma Index
0.37 0.46 0.37 0.55
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Street ConnectivityGrandLakes
No Trails
Grand Lakes
With Trails
Panther
Creek
Village
Houston
Heights
Street Pattern ConventionalCul-De-Sacs
HybridCul-De-Sacs
Cul-De-Sacs
Grid
Link Node Ratio1.11 1.38 1.10 1.65
Percentage of Cul-De-Sacs 0.39 0.14
0.41 0.03
Percentage of 4
Way Intersections 0.06 0.100.08
0.82
Street Density
(Miles/Area) 16.00 22.23 17.32 22.72
Alpha Index
0.06 0.19 0.05 0.33Gamma Index
0.37 0.46 0.37 0.55
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Street ConnectivityGrand
Lakes
No Trails
Grand Lakes
With Trails
Panther
Creek
Village
Houston
Heights
Street Pattern ConventionalCul-De-Sacs
HybridCul-De-Sacs
Cul-De-Sacs
Grid
Link Node Ratio1.11 1.38 1.10 1.65
Percentage of Cul-De-Sacs 0.39 0.14
0.41 0.03
Percentage of 4
Way Intersections 0.06 0.100.08
0.82
Street Density
(Miles/Area) 16.00 22.23 17.32 22.72
Alpha Index
0.06 0.19 0.05 0.33Gamma Index
0.37 0.46 0.37 0.55
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Street ConnectivityGrand
Lakes
No Trails
Grand Lakes
With Trails
Panther
Creek
Village
Houston
Heights
Street Pattern ConventionalCul-De-Sacs
HybridCul-De-Sacs
Cul-De-Sacs
Grid
Link Node Ratio1.11 1.38 1.10 1.65
Percentage of Cul-De-Sacs 0.39 0.14
0.41 0.03
Percentage of 4
Way Intersections 0.06 0.100.08
0.82
Street Density
(Miles/Area) 16.00 22.23 17.32 22.72
Alpha Index
0.06 0.19 0.05 0.33Gamma Index
0.37 0.46 0.37 0.55
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Summary of Findings: Street Connectivity
Among the Selected Neighborhoods:
The Highest in the Grid Neighborhood
Higher in Hybrid Cul-De-Sac than the
Conventional Cul-De-Sac
Street Density for Hybrid is higher thanConventional Cul-De-Sac & Comparable with
the Grid
Leading to Higher Cost for Development
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Pedestrian Accessibility for Parks
Accessibility for Parks
Aggregated
AerialDistance
Aggregated
NetworkDistance
PRD PCA
Grand Lakes withPed. Trails
Parks (6)0.86 1.30 1.51 0.38
Grand Lakes withoutPed.
Trails
Parks (6)
0.86 1.36 1.58 0.21
Houston Heights
Parks (10)1.10 1.57 1.65 0.51
The Panther Creek VillagePark (8) 0.94 1.45 1.54 0.22
(The Lower the PRD / The Higher the PCA Higher Accessibility)
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Pedestrian Accessibility for Parks
(The Lower the PRD / The Higher the PCA Higher Accessibility)
Accessibility for Parks
Aggregated
AerialDistance
Aggregated
NetworkDistance
PRD PCA
Grand Lakes withPed. Trails
Parks (6)0.86 1.30 1.51 0.38
Grand Lakes withoutPed.
Trails
Parks (6)
0.86 1.36 1.58 0.21
Houston Heights
Parks (10)1.10 1.57 1.65 0.51
The Panther Creek VillagePark (8) 0.94 1.45 1.54 0.22
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Pedestrian Accessibility for Parks
(The Lower the PRD / The Higher the PCA Higher Accessibility)
Accessibility for Parks
Aggregated
AerialDistance
Aggregated
NetworkDistance
PRD PCA
Grand Lakes withPed. Trails
Parks (6)0.86 1.30 1.51 0.38
Grand Lakes withoutPed.
Trails
Parks (6)
0.86 1.36 1.58 0.21
Houston Heights
Parks (10)1.10 1.57 1.65 0.51
The Panther Creek VillagePark (8) 0.94 1.45 1.54 0.22
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Pedestrian Accessibility for Schools
(The Lower the PRD / The Higher the PCA Higher Accessibility)
Accessibility for Schools
Aggregated
AerialDistance
Aggregated
NetworkDistance
PRD PCA
Grand Lakes withPed. Trails
Schools (2)1.06 1.47 1.39 0.31
Grand Lakes withoutPed.
Trails
Schools (2)
1.06 1.56 1.47 0.13
Houston Heights
Schools (11)1.05 1.36 1.31 0.52
The Panther Creek Village
Schools (2)0.89 1.30 1.46 0.34
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Pedestrian Accessibility for Schools
(The Lower the PRD / The Higher the PCA Higher Accessibility)
Accessibility for Schools
Aggregated
AerialDistance
Aggregated
NetworkDistance
PRD PCA
Grand Lakes withPed. Trails
Schools (2)1.06 1.47 1.39 0.31
Grand Lakes withoutPed.
Trails
Schools (2)
1.06 1.56 1.47 0.13
Houston Heights
Schools (11)1.05 1.36 1.31 0.52
The Panther Creek Village
Schools (2)0.89 1.30 1.46 0.34
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Pedestrian Accessibility for Retails
(The Lower the PRD / The Higher the PCA Higher Accessibility)
Accessibility for Retails
Aggregated
AerialDistance
Aggregated
NetworkDistance
PRD PCA
Grand Lakes withPed. Trails
Retails (3)0.80 1.18 1.48 0.21
Grand Lakes withoutPed.
Trails
Retails (3)
0.80 1.27 1.59 0.12
Houston Heights
Retails (0)N/A N/A N/A N/A
The Panther Creek Village
Retails (1)0.91 1.28 1.41 0.20
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Findings: Pedestrian Accessibility for Retails
(The Lower the PRD / The Higher the PCA Higher Accessibility)
Accessibility for Retails
Aggregated
AerialDistance
Aggregated
NetworkDistance
PRD PCA
Grand Lakes withPed. Trails
Retails (3)0.80 1.18 1.48 0.21
Grand Lakes withoutPed.
Trails
Retails (3)
0.80 1.27 1.59 0.12
Houston Heights
Retails (0)N/A N/A N/A N/A
The Panther Creek Village
Retails (1)0.91 1.28 1.41 0.20
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Summary of Findings: Pedestrian Accessibility
Among the Selected Neighborhoods:
Ped. Catchment Area is the highest in the Grid
Between Grid and Cul-De-Sac:
In terms of PRD, Higher Accessibility in the Grid
Between Cul-De-Sac neighborhoods:Mostly, Hybrid CDS > Conventional CDS
High Accessibility to Retails in Conventional CDS Reinforcing the Importance of Neighborhood
Design
Background |Research Questions | Neighborhoods | Analytic Methods | Findings | Conclusions & Implications
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Conclusions and Implications
Implications?
Market appreciates Pedestrian Friendly Features in
Suburban Neighborhoods -> Recognizing the Demand This Preference is Expressed in Different Way
Integrate Cul-De-Sacs with Ped. Oriented Features
Walkability Benefits Outweighed Dev. Costs
Radburn as an Old Wisdom ? (Lee and Ahn, 2003)
Might be Politically & Physically More Feasible Alt. Types of Streets Neighborhood Design
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Thank you very much
Question?
Chang Yi
Community and Regional PlanningUniversity of Texas at Austin