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1 Preferred citation style Axhausen, K.W. (2007) Catchment areas, social network geographies and travel: A conceptual model, presentation at the Annual Meeting of the Israeli Association of Transportation Research, Haifa, March

2 Catchment areas, social network geographies and travel: A conceptual model KW Axhausen IVT ETH Zürich March 2007

3 Time-scaled road -Switzerland (1950 and 2000) Scherer,

4 Quality adjusted prices for cars 1400 Qualitätsbereinigter Preisindex (2004 = 100) [%] Frei, 2004 Raff und Trajtenberg, 1990 Frei, Jahr 4

5 Price deflation for telecommunication US International and interstate average revenue per minute Index [1995 = 100] Nach FCC (2001) Year 5

6 Size of goods markets and productivity: A hypothesis Capital/Wages Economies of scale Economies of scope - - Innovation GDP - Prices - Monopolies Transport system and demand k - Market size Energy costs - Elasticity > 0 Elasticity < 0 k: Generalised costs of travel (excluding externalities) 6

7 Size of goods markets and productivity: A hypothesis Economies of scale Economies of scope GDP - Activity Fleet comfort slots - vtts et al. Tours - - vkm t/pkm k - Energy costs Market size - Elasticity > 0 Elasticity < 0 Slots: possibilities to move goods or people For a given infrastructure and commercial and private fleet 7

8 Response: VTTS (free-flow) 8 Axhausen, Hess, König, Bierlaire, Bates and Abay, 2006

9 Response: Swiss commuting speeds since % 90% Cumulative distributon 80% 70% 60% 50% 40% 30% 20% 10% 0% Speed (km/h) 1970 Transit 1980 Transit 1990 Transit 2000 Transit 1970 Car 1980 Car 2000 Car MIV

10 First summary On-going reduction in the generalised cost of travel Expanded market areas and improved economic productivity 10

11 Social networks 11

12 Definition of a social network The topology of a social network describes Which person/firm (node) is linked to which other persons/firms By contacts (links) of a certain quality (impedance or cost) Closeness ~ 1/Impedance 12

13 Spatial density and social connectivity Dense/tight Dense/loose Sparse/tight Sparse/loose 13

14 Travel and social networks Maintenance of the networks requires: Face to face contacts Balanced by other forms of contacts Travel ~ Physical spread of the contacts Trade-off between loosing contacts and social capital and investing in new contacts closer to home 14

15 Average size of travel party (2003 Thurgau) Short vacation Excursion: nature Other Excursion: culture Meeting friends Further education (leisure) Garden/ cottage Voluntary work Disco, pub, restaurant, cinema Meeting relatives/family Window shopping Pick up/drop off/attendance Group/club meeting Family duty Cemetery Active sports Education Long-term shopping Walk or stroll Daily shopping Private business Private business (doctor,... Work Household members travelling along Other persons travelling along Dog travelling along Mean 15

16 In-commuter sheds of the ten largest Swiss towns Nach Botte,

17 Example of a social network geography Ohnmacht, 2004 Female, 28, 4 moves, Public transport user 17

18 Example geography of a 35 old female 18

19 How to measure? Team: S. Schönfelder, IVT M. Balmer, IVT R.K. Rai and V.S. Vaze, IIT interns Funding: ETH research fund 19

20 How to measure? Parametric: 95% confidence ellipse (form and type of distribution) Semiparametric: Inclusion geometries (form of geometry) (Weighted) shortest path networks (structure of path) (Percentage) Minimum convex poligons (convexity) Kernel density estimator (form of estimator) Mean harmonic home ranges (form of estimator) Non-parametric Observed path geometries 20

21 Measures: Confidence ellipse 21 Schönfelder, 2006

22 Measures: Kernel densities 22 Schönfelder, 2006

23 Measures: Inclusion geometries Find: s.t. with: min A i (β i1... β in ) Area A i covering p% of all observed points i : Type of geometry (Ellipse, bean, Cassini...) p : Predetermined share, e.g. 95% 23

24 Measures: Inclusion geometries home location shop location shop cassini shop bean shop superellipse shop ellipse y coordinate x coordinate 24

25 Measures: Minimum convex poligons (MCP) Schönfelder, 2006 MCP Percentage MCP 25

26 Measures: Shortest path network 26 Schönfelder, 2006

27 Measures: Weighted shortest path network Schönfelder,

28 Survey work Team: A. Frei, IVT T. Ohnmacht, Universität Basel/FH Zentralschweiz, Lucerne J. Larsen, Roskilde University J. Urry, Lancaster University Funding: ifmo, DfT, BBW/Cost, SNF 28

29 Items to capture the social network geographies Name generators Name interpreters Type and length of contact Frequency by mode of contact Home location Second homes Detailed descriptions of face-to-face contacts 29

30 Items to characterise the mobility biography Home and second home locations Work and school locations Household composition Mobility tools Main mode (to work/school) (Major holidays) Personal income Household income 30

31 Response behaviour in the Cost/ifmo surveys Phase Pretest Main study Share of total Sample % Wrong address % Not reachable by phone % Share of reached by phone Reached by phone % 100% Recruited % 11.7% Interviewed % 11.2% Post-interview questionnaire returned % 10.8% 31

32 Contacts 32

33 Distance distribution Frequency Distance 1'000 10' '000 33

34 Contact frequency by mode Electronic contacts Face-to-face contacts Mean annual frequency Mean distance in the decile [km] 34

35 Market share by contact mode Average contacts per year 60% 50% 40% 30% 20% 10% Face-to-face (Female) (Female) Face-to-face (Male) (Male) Phone (Female) SMS (Female) Phone (Male) SMS (Male) 0% Median distance of the quartile [km] 35

36 Distribution of the social geographies Frequency E2 1E3 1E4 1E5 1E6 1E7 1E8 1E9 95% Confidence ellipse of the social network geography Japan: 378; U.S.A: [10 3 km 2 ] 36

37 Future trends: Hypotheses 37

38 Hypotheses Message costs - - k Number of networks Migration Network geography Professional activity space Personal activity space Left skew of intensity distribution Network overlap - Local anomie - Elasticity > 0 Elasticity < 0 38

39 Expected impacts: Improved welfare The social networks should be more homogeneous and therefore more productive for their members But, the selectivity excludes the less attractive persons who are disadvantaged through a reduced ability to travel or a reduced ability to participate in activities But, the dependence on commercial or state-provided services for care increases 39

40 Next steps 40

41 Changing our unterstanding of travel Budget constraints Capability constraints Generalised costs of the schedule Generalised cost of travel Generalised cost of activity participation Risk and comfort-adjusted weighted sums of time, expenditure and social content 41

42 Research issues Measurement of the activity spaces (geographies, markets) Estimate of historical activity spaces... Taste differences in network form and geography Social/cultural preferences for network form and geography Stability of the geographies under pressure Elasticities to policy (or environmental) change Time until trend change 42

43 Policy questions Is happiness still growing? How large are the social externalities? How stable is the overall system under pressure? 43

44 The hypotheses summarized Wages Elasticity > 0 Elasticity < 0 Activities Fleet comfort Specialisation Tours - vkm Housing consumption - vtts et al. Energy costs pkm - k Number of networks - Migration Professional and personal activity space - Network overlap Network geography - Local anomie 44

45 Literature and references See 45

46 Appendix: Dynamics of social networks 46

47 Social networks: Hypotheses [1] The size of the social network geography is inversely proportional to the generalised costs of travel and communication [2] The number of contacts individuals maintain is inversely proportional to the generalised costs of travel and communication [3] The probability of being linked to a member of one s network through multiple networks increases with the spatial density of one s contacts [4] The distribution of effort on non-household members will become more left skewed as the spatial social network tightness decreases [5] The knowledge about the contacts of contacts in a social network is proportional to the generalised costs of travel and communication 47

48 Social networks: Hypotheses (2) [6] The activity space of an individual is proportional to its social network geography [7a] The size of the local activity space of an individual stabilises after an initial exploration. [7b] The size of the total activity space will grow in line with the growth of social network geographies. [8] The reliance on commercial or publicly funded personal services increases proportionally with the geography of social networks [9] The welfare of the individuals should increase inversely proportional to the generalised costs of travel 48

49 Appendix: Preliminary results (Cost/ifmo survey) 49

50 Poisson regression of the number of social contacts Variable Mean St. dev Beta Standardised beta Sign. Constant Age [years] Age 2 /1000 [years 2 /1000] Data_horizon [y/n] Data_COST 355 [y/n] Number of relocations [n] University degree [y/n] N 128 Adjusted R

51 Probit results of contact modes Variable Category Market shares of contact modes Phone SMS Age Sex: Male Face-toface Educatio Type of contact Compulsory school Apprenticeship Baccalaureat Reference Reference Reference Reference Professional tertiary University degree Others and friends Family and partner Work mates Ln (distance) Income Income * Male Adjusted R 2 /Chi N

52 Tobit results of social geography size Variable Mean St. dev Beta Standardised beta Sign. Data_ifmo [y/n] Male [y/n] Age [years] University degree [y/n] Car ownership [y/n] Annual or monthly public transport ticket [y/n] Number of relocations [n] N 117 Adjusted R