Accessibility: an academic perspective

Transcription

1 Accessibility: an academic perspective Karst Geurs, Associate Professor, Centre for Transport Studies, University of Twente, the Netherlands Presentatietitel: aanpassen via Beeld, Koptekst en voettekst 1

2 Whatis accessibility? Accessibility is a slippery notion one of those common terms that everyone uses until faced with the problem of defining and measuring it (Peter Gould, 1969) 2

3 Gap between academic literature and practice A distinct gap currently exists between the academic literature and the practical application of accessibility measures. It is important that accessibility measures used in practice are theoretically and behaviourally sound and that innovative approaches to measuring accessibility are made practical (Handy and Niemeier, 1997) 3

4 Choice of indicator determines conclusions Inner London has the highest access costs (in terms of time and vehicle operation costs) in the UK, but the highest level of potential accessibility to jobs, despite the high travel cost. (Linneker and Spence, 1992) 4

5 Definition of accessibility: (Geurs, K.T., van Wee, B., Accessibility evaluation of land-use and transport strategies: review and research directions. Journal of Transport geography 12, ) Indicator for the impact of land-use and transport developments and policy plans on the functioning of the society in general. Should relate to the role of transport in society; to provide individuals the opportunity to participate in activities in different locations. Definition (passenger travel) the extent to which land-use and transport systems enable (groups of) individuals to reach activities or destinations by means of a (combination of) transport mode(s) (at various times of the day). 5

6 Componentsof accessibility (Geurs, K.T., van Wee, B., Accessibility evaluation of land-use and transport strategies: review and research directions. Journal of Transport geography 12, ) The land-use component reflects the land-use system, consisting of the amount, quality and spatial distribution of opportunities The transportation component describes the transport system, expressed as the disutility for an individual to cover the distance between an origin and a destination using a transport mode; The temporal component describes the availability of opportunities at different times of the day, and the time available for individuals to participate in certain activities The individual component reflects 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. 6

7 (Geurs, (Geurs, K.T., van K.T., Wee, van B., Wee, Accessibility B., evaluation Accessibility of land-use evaluation and transport of land-use strategies: and review transport and research strategies: review and research directions. directions. Journal of Journal Transport of Transport geography 12, geography ) 12, ) 7

8 Four main perspectives on accessibility Infrastructure-based measures (transport planner s perspective) Location-based measures (urban planner s perspective) Person-based measures (space-time geography) Utility-based measures (economist s perspective) 8

9 Infrastructure-based accessibility 9

10 Simple location-based measure: Cumulative opportunities/contour measure Trip likelihood 1 0 Time, cost 10

11 Time isochrone/cumulative opportunities: Amsterdam, car, morning peak hour, 2008 Interactive website national accessibility map ( 11

12 Potential accessibility measure (gravity-based; Hansen-based) A i = n j= 1 D e j βc ij 12

13 Potential job accessibility by car, peak hour,

14 Simple is beautiful, but: Location-based measure have no meaning either in terms of costs and benefits and/or activity values Often simple and aggregate measure are used, not linked to transport models. Choice of maximum travel time or distance decay function has large impact on the outcome Not easily linked with transport policy goals; not applicable in economic appraisal Demand oriented; competition effects are not included 14

15 More advanced location-based measures: potential accessibility with competition A i = n = m j 1 k= 1 GP k j P F( d jk F( d ) ij ) Joseph, A.E., Bantock, P.R., Measuring potential physical accessibility to general practitioners in rural areas: a method and case study. Social science and Medicine 16,

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17 T ij = a i b j F(c ij ) Inverse balancing factors of the doubly constrained spatial interaction model a i = n j= 1 1 βc D je j b ij 17

18 Job accessibility by car Job accessibility by public transport South west Job potential North east Balancing factor Geurs, K.T., Eck, J.R. Ritsemavan, Urbanisation, accessibility and the environment (in Dutch). RIVM, Bilthoven. Geurs, K.T., Eck, J.R. Ritsemavan, Accessibility evaluationof land-usescenarios: the impact of job competition, land-useand infrastructuredevelopments forthe Netherlands. Environment and Planning B: Planning & design 30, South west North east Job potential Balancing factor 18

19 Potential accessibility measures with competition Pro s: methodologically better, takes inbalance in distribution of demand and supply in activities into account Con s: more difficult to interpret Suitable for destinations with capacity restrictions (jobs, hospital beds, school places, etc.) Matching job requirements and worker s education level is also very important 19

20 Recent progress in location-based accessibility Increasing level of detail: population/employment segmentation; high spatial resolution (block-level) using GIS, e.g. Chen et al., Univ of Califoria (TRB paper 2011) Link with detailed transport models: travel times/costs by time of day Evaluate the extent of distributional justice, measure spatial (in-) equity in the provision of opportunities 20

21 Person-based measures Time-Space Geography Analysis of accessibility at the individual level Accessibility strongly depends on individual constraints (activity scheduling), temporal constraints (opening hours of shops), spatial contraints (travel budget) Requires huge amount of data, is difficult to operationalise and is demand oriented (no competition effects) 21

22 Progress in person-based accessibility measures In recent years, practical applicability has been improved, activity-based transport models have been developed using synthetic population data, reducing the data collection effort Travel data collection using Smartphones will strongly increase possibilities to develop person-based accessibility measures; enabling comparisons with location-based measures 22

23 Economist s perspective: utility-based measures Benefits that people derive from access to spatially distributed activities Simple measures of composite travel cost Accessibility benefit measures based on double constrained transport model (Martinez, 1995; Martinez and Araya, 2000) Logsum accessibility benefit measures based on discrete choice models (Ben-Akiva and Lerman, 1985) 23

24 Example: logsum accessibility benefit measure (Geurs et al., Accessibility appraisal of integrated land-use/transport policy strategies: more than just adding up travel time savings. Transportation Research Part D 15, ) Logsum is the log of the denominator in the MNL model -> utility of a choice from a set of alternatives; can be transformed into monetary units. Money talks! Logsum accessibility benefits from land-use changes may be large, particularly for slow modes Accurate benefit measurements when land use changes 1000 million euro per year 2 1,5 1 0,5 0-0,5 Compact urban development Climate and flood risk scenario Uplands scenario Compact urban development Climate and flood risk scenario Uplands scenario ROH Logsum -1-1,

25 Utility-based measure may give different results than location-based measures. Utility-based measures show diminishing returns, i.e. assumes non-linear relationships between accessibility improvements and user-benefit changes. The measure may indicate that it is better to improve accessibility for individuals at locations with low accessibility levels (e.g. peripheral regions) than at locations that are already well accessible (e.g. central urban areas) (e.g. Koenig, 1980; Geurs and Ritsema van Eck, 2001). 25

26 Component Measure Transport component Land-use component Temporal component Individual Component Infrastructurebased measures Travelling speed; Vehicle-hours lost in congestion Peak-hour period; 24-hr period Trip-based stratification, Location-based measures Travel time and or costs between locations of activities Amount and spatial distribution of the demand for and/or supply of opportunities Travel time and costs may differ Stratification of the population Person-based measures Travel time between locations of activities Amount and spatial distribution of supplied opportunities Temporal constraints for activities and time available for activities Accessibility is analysed at individual level Utility-based measures Travel costs between locations of activities Amount and spatial distribution of supplied opportunities Travel time and costs may differ Individual or homogeneous population group level 26

27 Choice and operationalisation of accessibility measures depend on: 1. Study goal, e.g., evaluation of economic effects and equity effects implies detailed accessibility measures 2. Scientific quality: treatment of different components and elements within these components. 3. Applicability/operationalisation Quality of data and transport model High resolution and multimodal accessibility estimations improve quality of policy evaluations 4. Interpretability /communicability Accessibility measures can be complex, but understandable if well visualised and interpretable units are used (scaling to average/maximum, indices; money, etc.) 27

28 Keymessages: The ideal accessibility measure does (and will) not exist. In recent years, academic studies focused on increasing level of detail of analysis, space-time and utility-based measures There is a trade off between academic quality and applicability in practice The definition and operationalisation of accessibility strongly affects the conclusions: different accessibility measures may give very different conclusions -> develop a toolbox of accessibility measures which allows comparisons of measures. 28

29 Thank you for your attention! Contact: 29