The Glossary of the Action “Accessibility Instrument for Planning Practice” was born in order to create a common language/understanding between all the participants of the Cost Action. To reach this goal, all members of the Action were involved in choosing the terms to define and their meanings in a participatory way. The Glossary of the Action is not static but a dynamic source of continuous debate. It is the result of a collaborative process started in the early stage of the Action.
A baseline document for further discussions was proposed during the first stage of the work of the Action, in order to better explain the accessibility instruments survey (see Hull et. al., 2012) and it was published in the action website during the first year of work. This document received several comments by the action members suggesting to add, eliminate or modify some terms. Based on this web discussion, a first version of the Glossary was produced and published in the first Report of the Action (Papa and Angiello, 2012). As the authors stressed, the first version of the Glossary was not supposed to be a final product, but the first step of a continuous process. Keeping this in mind, in June 2013, during the second Summer Training School in Tui-Valença, the Junior Research Network of the Action launched a debate in order to wider the previous version by including a broader range of new terms. The work here presented resumes the main conclusions of this collaborative process.
Accessibility (evolution of the definition)
- “the opportunity which an individual or type of person at given location possesses to take part in a particular activity or set of activities” (Hansen,1959).
- “the average opportunity which the residents of the area possess to take part in a particular activity or set of activities” (Wachs and Kumagai, 1972).
- “the accessibility of a point in a system is a function of its location in space with respect to all other points in the system” and “implies relative nearness either in the sense of a direct linkage or a minimum expenditure of travel cost or time” (Hack, 1976 and de Lannoy, 1978).
- “the consumer surplus, or net benefit, that people achieve from using the transport and land-use system” (Leonardi, 1978).
- “the ease and convenience of access to spatially distributed opportunities with a choice of travel” (U.S. Department of Environment, 1996).
- “the extent to which the land use-transport system enables (groups of) individuals or goods to reach activities or destinations by means of a (combination of) transport mode(s)” (Geurs and van Eck 2001);
- “ the amount and diversity of places that can be reached within a given travel time and/or cost” (Bertolini, LeClercq and Kapoen, 2005).
- “the ease in meeting one’s needs in locations distributed over space for a subject located in a given area” (Cascetta, Cartenì and Montanino, 2013).
A tool that aims to provide explicit knowledge on accessibility to actors in the planning domain, a tool of measure, interpretation and modelling of accessibility, developed to support planning practice (analysis, design support, evaluation, monitoring etc.). Mostly, it consists of computer model(s) that transfers data/information about urban systems into meaningful knowledge, by providing visualization tools such as maps or numerical indicators. Accessibility Instruments can be (Papa and Angiello, 2012):
- Measuring attributes of places or people – e.g. planning tools to identify how to make places more liveable or ways of identifying the opportunities available to people when planning new facilities or destinations;
- Analytical methods to apply accessibility principles within planning – e.g. parking policy standards based on accessibility criteria or public transport service delivery requirements based on people’s accessibility needs;
- Models to understand dynamic effects and connectedness in transport networks, in particular the dynamics between spatial plans and transport investments;
- Indicator calculation methods where indicators are used to audit, monitor or set standards for planning policies.
Accessibility measures are used to translate the concept of accessibility in quantitative indicators that take into account both the socio-economical and the transportation systems (Papa and Angiello, 2012). Each accessibility measure has a general conception and a general formulation of its accessibility indicator (infrastructures-based measures, contour measures, gravity measures, competition measures, utility-based measures, network measures, time-space measures).
Active accessibility of a certain zone is a proxy of the ease of getting to the activities located in different zones of the study area for a given purpose (e.g. workplace, shopping), moving from (Cascetta, 2009).
These measures are able to consider the effects of competition in the origin and/or destination. The effects are usually located in urban areas where competitiveness concerns or users seeking opportunities and/or opportunities competing for users, when users are insufficient to enable the range of opportunities (Silva, 2008). The measure calculates all potential users of an activity in an area as well as all potential activities, trying to balance the relationship between the number of users and activities.
Components of accessibility
In Geurs’ and van Eck’s (2001) understanding, accessibility consists of four components:
- Land use component (of accessibility) – The land-use system, consisting of the amount, quality and spatial distribution of identifiable opportunities.
- Transportation component (of accessibility) – The transport system, expressed as the disutility for an individual to cover the distance between an origin and a destination using a transport mode.
- Individual component (of accessibility) – The needs, abilities (depending on people’s physical condition, availability of travel modes, etc.) and opportunities (depending on people’s income, travel budget, educational level, etc.) of individuals.
- Temporal component (of accessibility) – The availability of opportunities at different times of the day, and the time available for individuals to participate in certain activities.
Furthermore, these components may be affected by accessibility through feedback mechanisms.
(also known as cumulative opportunities or isochronic measures) count the number of opportunities/activities available within a given travel time, distance or cost (fixed costs), or measure the (average or total) time or cost required to access to a fixed number of opportunities/activities (fixed opportunities) (Geurs and van Eck, 2003).
Decision Support System (DSS)
A computer-based information system that supports decision-making activities. DSS serve the management, operations, and planning levels of an organization and help to make decisions, which may be rapidly changing and not easily specified in advance. (Papa and Angiello, 2012).
Are based on the concept of attraction and impedence. These measures assumes that accessibility of a given zone is proportional to the attractiveness of destinations surrounding (e.g. the distribution of population, employment, income, etc.) and inversely proportional to the spatial impedance of travel required to reach those destinations (e.g. travel time, distance, generalized cost etc.) from all other zone of the study area.
These measures mainly focus the characteristics of the infrastructure and analyze the performance of the transport system as a whole.
The mobility concept is understood by the movement (or flow) of people, goods and information (also considered as “virtual mobility”) corresponding to relocation needs. This concept assumes that the mere increase of “travelling miles” or speed between two points benefits people, however does not take into consideration the distribution of opportunities in the territory. Mobility and accessibility are considered the “ying and yang” of planning (Ross, 2000).
A group of measure based on graph theory and network analysis that correlate accessibility with topological measures of the transportation network. In some case this measures can include also the land use component of accessibility (Papa and Angiello, 2012).
Passive accessibility is a proxy of the opportunity for a certain activity located in the zone of being reached by the potential “users” coming from all the other zone of the study area for a given purpose (e.g. the clients of a shop) (Cascetta, 2009).
Perceived Opportunity Measures
The number of opportunities perceived by an (average) individual for satisfying his/her needs in the study area (Cascetta, Cartenì and Montanino, 2013).
Place Rank Measure
Place Rank measure is based on the methods used by search engines such as Google to rank Web pages. This measure assume that the level of accessibility in a certain zone of the study area is determined based on the number of people coming to this zone to reach an opportunity, where each person contributes to the accessibility level in the zone to which he commutes with a different power. The power of the contribution of this person depends on the attractiveness of his/her zone of origin as final destination (El-Geneidy and Levinson, 2006).
Planning, as a general activity is the making of an orderly sequence of action that will lead to the achievement of a stated goal or goals (Hall, 2010).
Planning Support Systems (PSS)
PSS is a subset of geoinformation-based instruments that incorporate a suite of components (theories, data, information, knowledge, methods, tools, etc.) that collectively support all of, or some part of, a unique planning task (Geertman and Stillwell, 2003).
Spatial separation measures
Measures travel impediment or resistance between origin and destination, or between nodes. Travel impediment measures can include: Physical (Euclidean) distance Network distance (by mode), travel time (by mode), travel time (by network status—congestion, free-flow, etc.), travel cost (variable user cost or total social cost) (Curtis and Scheurer, 2010).
The part of the planning process that is concerned with the regulation and management of changes to land use and development. (Wikipedia)
Measures travel opportunities within pre-defined time constraints. (Curtis and Scheurer, 2010)
Use of a wide range of modeling concepts to capture and reproduce any type of physical or socioeconomic phenomena observed in urban systems, allowing the forecast of potential evolutions under controlled conditions to assist planning or decision-making processes in general (Papa and Angiello, 2012).
Usability (of an instrument)
A qualitative indicator of the extent to which an accessibility instrument is accepted and applied in planning or decision making process by its end-users (Papa and Angiello, 2012).
Measures individual or societal benefits of accessibility. This can occur in monetarised form as a measure of economic utility, or as an indicator for social equity (or for other sustainability objectives). It can also be applied as a behavioral indicator, measuring the value individuals afford to the accessibility of particular activities (Curtis and Scheurer, 2010).
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