assessment of pedestrian accessibility and prioritization of future improvements
TRANSCRIPT
A GIS-based model for Assessment of Pedestrian Accessibility and Prioritization of Future Improvements
Mengyuan XuWashington State UniversityDoctor of Design Candidate
Image:www.123rf.com
Page 2
The access to public goods and services is commonly considered as an important factor in urban planning policy making process and has received large research interest for decades.
Since all social welfare issues relate to the distribution of supply of social services among social groups, all public policies naturally are related to the notions of:
- Equity
- Accessibility
Background
http://www.unmalawi.org/images/access-to-urban-service.jpg
Page 3
Equity
Lack of consensus on a consistent understanding in planning literature
Two principles of equity
– Horizontal Equity
“In which everyone receives the same public benefit, regardless of socioeconomic status, willingness or ability to pay, or other criteria” (Talen 1998)
– Vertical Equity
“Equity in the distribution of public resources need to response to the need of groups” (Crompton and Wicks1988)
Background – Key Concepts
Page 4
Definition of Equity in my research:
“Individuals and groups that differ in need and ability are treated differently in order to be provided with equal opportunities to resources.”
Definition of Inequity:
“Differences in access to resources among subgroups of citizens”.
Background – Key Concepts
Page 5
Accessibility
Widely considered as a significant goal in urban planning
Defintion
– “…reflects the possibilities for activities, such as working or shopping, available to residents of a neighborhood, a city, or a metropolitan area.” (Handy & Clifton 2001)
– “An individual’s ability to reach desired goods, services, activities and destinations” (Litman 2002)
Three-fold framework
– Social-demographic data
– Geographic data of urban services
– Travel options
Background – Key Concepts
Page 6
Measures of Transportation Accessibility
– Block length (mean)
– Block size (mean area)
– Block density
– Intersection density
– Link-Node Ratio (LNR)
– Pedestrian Route Directness (PRD)
– Service area calculation
– Walking distance to activities
Background – Key Concepts
Page 7
Life Need Service Facilities
“A system of physical facilities/services that support the essential needs of individuals, families and communities and thus enhance the overall quality of life”
– Daily Food Provider: Groceries and convenience stores
– Social Gathering: Libraries, community centers, and churches
– Recreational facilities
– Healthcare and social assistance: hospitals, and clinics;
Background – Key Concepts
Page 8
Life Service Deserts:
“Areas with relatively poor access to life need services”
Suburban sprawl since the 1940s
– Automobile-oriented transportation planning
– Separation of land uses
– Commercial service providers moved out of inner cities to new developed suburbs
16.1 percent of households in Spokane City do not own a private car.
Mobility disadvantaged groups may be highly reliant on access to pedestrian networks with ADA facilities
Measuring accessibility and service deserts based on pedestrian networks has received great interest.
Background – Key Concepts
Page 9
Prioritization
In the context of limited resources and budgets, it is vital to identity the importance of each missing link in the network in order to decide its priority when planning network improvements.
Efficiency and Equity are considered as critical factors to improve the performance of urban environment in previous literatures (Litman 2002; Talen 2011).
Background
Page 10
Propose a GIS-based accessibility assessment model that:
Identifies the inequities in spatial access to life needs services facilities in my study area, or say, life need service deserts for all citizens and/or targeted groups;
Evaluates how the level of accessibility would be affected by proposed interventions by predicting and describing the potential consequences;
Implements methods to prioritize potential infrastructure improvements.
Research Goals
Page 11
The majority of existing research favors motorized accessibility and relatively little attention has been paid to pedestrian accessibility (Litman 2002).
Recent accessibility research focusing on the pedestrian environment, it has tended to use street networks for connectivity analysis of the built environment, instead of true pedestrian networks (Chin et al. 2008).
Previous measures tend to separate the individual socio-economic and socio-demographic status from its geographical context (Weber & Kwan 2003)
Gaps in Existing Researches
Page 12
We are at the digital threshold of the computer-aided design tools evolution to next stage, which would be simulation tools.
Representational tools
– Describing “what it is”
– Their functions are limited in drafting and documenting.
Simulation tools
– Predicting “what can be”
– A true design decision supporting tool helping designers evaluate different future scenarios and find the optimal one
Concept of GeoDesign
Page 13
Study Area: Spokane Transit Public Benefit Transportation Area (PTBA)
Spokane Pedestrian Network (PNET) model
A fine grained representation of the pedestrian network with detailed and accurate information about all potential pedestrian pathways and facilities, including availability of sidewalks, ramps, marked road crossings, and potential barriers in Spokane Transit’s Public Benefit Transportation Area (PTBA)
Life Need Service Facilities: The location data of these services facilities are categorized by North American Industry Classification System (NAICS).
Demographic Data: The population data is gained from 2010 US census data at the census block level. The car ownership information is from 2010 American Community Survey.
Methodology Study Area
Page 14
Methodology Pedestrian Network
Page 15
The target census block groups selected based on the rate of vehicle ownership. The rate of vehicle ownership is calculated based on the data of total population and the number of vehicles for each census block group.
Methodology – Targeted Groups
Page 16
Route Calculation
– Routes in this study are defined as the Origin-Destination (OD) Pairs that are from census block centroids to various Life Needs Service Facilities locations.
– ArcGIS Network Analyst toolset
– ¼ mile (400 meters) as accessible
Aim: identify the important pedestrian pathways in the network
Methodology
Page 17
Methodology
Healthcare facilities
Routes from all centroids
Routes from targeted centroids
Page 18
Importance Identified for the missing links
The measure of Efficiency Importance of each missing sidewalk segment is defined as the accumulated number of residents based on all routes to all categories of Life Need Service Facility Destinations. The specific missing segment population is proportional to the total missing segments on the route. The data of number of people is acquired from the census block that the centroids represent.
Methodology
Page 19
The Equity Importance is defined as the accumulated numbers of residents in the targeted census block groups based on all routes to all categories of Life Need Service Facility Destinations that one certain segment has been recorded.
Methodology
Page 20
Data Analysis
Population served per length
Page 21
Data Analysis
Page 22
Data Analysis
Overall Importance = Efficiency Importance + Equity Importance * r
where r = ratio of the emphasis between Efficiency and Equity
In my research, r = 1, which gives the equal importance for the two measures. The setting of the weight value r equation allows analysts flexibility to adjust the r value based on different viewpoints.
References:Chin, G.K.W., Van Niel, K.P., Giles-Corti, B., & Knuiman, M. (2008). Accessibility and connectivity
in physical activity studies: The impact of missing pedestrian data. American Journal of Preventive Medicine, 46(1), 41-45.
Crompton, J.L. & Wicks B.E. (1988). Implementing a preferred equity model for the delivery of leisure services in the US context. Leisure Study, 7(3), 287-304.
Handy, S. L., & Clifton, K. J. (2001). Evaluating neighborhood accessibility : possibilities and practicalities. Journal of Transportation and Statistics, 4(2), 67-78.
Litman, T. (2002). Evaluating Transportation Equity. World Transport Policy & Practice, 8(2), 50-65.Talen , E. (1998). Visualizing Fairness: Equity Maps for Planners. Journal of the American Planning
Association, 64(1), 22-38Talen, E. (2011). Geovisualization of Spatial Equity. In Handbook of GIS and Society Research,
Nyerges, T., Couclelis, H., & McMaster, R., 458-479. Sage Publications.Weber, J., & Kwan, M. (2003). Evaluating the Effects of Geographic Contexts on Individual
Accessibility: A Multilevel Approach. Urban Geography, 24(8), pp. 647–671.
.
Thank you
Mengyuan [email protected]