Stability and innovation of human activity spaces http://www.ivt.ethz.ch/vpl/publications/reports/ab258.pdf Stefan Schönfelder * IVT - Institute for Transport Planning and Systems ETH - Swiss Federal Institute of Technology Zurich January 2005 * with thanks to KW Axhausen
Intra-personal level of mobility Behavioural variability Inter-personal level Single day Person 1 Person 2 Person 3 Person 4 e.g.sum of travel time Intra-personal level e.g.sum of travel time Person X Person 5 Mean Mo Tu We Th Fr Sa Time 2
Long-term issues in travel behaviour Temporal phenomena: Behavioural issues over time Stability Regularity / Rhythms Variability Dynamics Spatially: How may locational choice and the intensity of individual usage of urban space be visualised and measured? (Geocoding/GPS facilitate) 3
Data sources Place Duration Mode Travel diaries: Uppsala 1971 5 weeks All Mobidrive 1999 (Karlsruhe, Halle) 6 weeks All Zürich 2001 (Leisure only) 12 weeks All Thurgau (CH) 2003 6 weeks All GPS studies: Borlänge 2000-2002 up to 80 weeks car (240.000 trips) Copenhagen AKTA 2001-2003 24 weeks car Commute Atlanta 2004 > 52 weeks car 4
Activity space: Concept (Micro-geographical) Indicator for individual space use Geometrical (two-dimensional) form based on distribution of visited activity locations over time OBSERVED behaviour Individual panel data allows physical mapping / listing / enumeration of visited locations and travel demand in-between Several conceptual studies with focus on travel potentials (e.g. space-time prisms) Friend s place Work place Home Business place But: Few empirical work due to missing data Second shop Sports First shop Locations Travel 5
Assumed relationship between act. space and costs Size of activity space Hysteresis because of investment in social capital and mental maps Increasing costs Decreasing costs (Generalised) Travel costs 6
Issues Size of activity spaces Number of places visited Structure of activity spaces Innovation in destination choice 7
Measuring the size of activity spaces: Problems Transformation of information about the places of contact Social relationships Origin/Destination Sale or usage in a low-dimensional measure of Comparison over time (for one traveller) Comparison between travellers 8
Example: Visited places over 6 weeks (local) Schönfelder und Axhausen, 2004 12000761 Woman, 24 Fulltime work, single 216 trips in 6 weeks 9
Example: Commuters to Zürich (2000) 10 Axhausen, Botte und Schönfelder, 2004
Approaches Parametric : 95% confidence ellipse Non-(semi)-parametric : Spatial smoothing (kernel density estimates) Network of shortest trips Network of monitored trips 11
Approach 1: 95% confidence ellipse Concept: Probability Axhausen, Botte und Schönfelder, 2004 Smallest possible area of a true value of the population (i.e. activity locations) Measure: Area Shows dispersion / concentration 12
Example: Zürich commuters (2000) 13 Axhausen, Botte und Schönfelder, 2004
Number of trips in 6 weeks 60% 60% 50% 50% 40% 40% 30% 30% 20% 20% 10% 10% Schönfelder und Axhausen, 2004 0% 10 20 30 40 50 >50 All trips Car trips Mobidrive; All trips of respondents Car trips of car users 0% 10 20 30 40 50 >50 Car trips Borlänge GPS; Car trips of car users 14
Mobidrive: 95% confidence ellipses Schönfelder und Axhausen, 2004 200 180 160 140 120 N 100 80 60 40 20 0 20 60 100 140 180 220 260 300 [sqkm] * Local trips only 15
Variance of activity spaces over time Correlation coefficient Last period Trips Places 95% CE This period Trips Borlänge Copenhagen 0.71 0.66 Schönfelder und Axhausen, 2004 Places 95% CE N periods Borlänge Copenhagen. Borlänge Copenhagen Borlänge Copenhagen 849 252 0.62 0.62 849 252 0.62 0.52 849 252 16
Number of unique locations Unique location is defined as a combination of Address (street address, zip code, municipality code etc.) Activity purpose Systematic problem of GPS data: How to summarise varying parking positions to a single location? 17
Number of places as function of number of trips (Thurgau 2003) 100 Schönfelder und Axhausen, 2004 Number of locations 80 60 40 20 0 0 100 200 300 400 Number of trips 18
Number of places as function of number of trips Slope R 2 Mobidrive All Car drivers 0.18 0.22 0.47 0,71 Thurgau All Car drivers 0.22 0.25 0.37 0.73 Schönfelder und Axhausen, 2004 Uppsala Copenhagen Borlänge All Car drivers Car drivers Car drivers 0.22 0.25 0.28 0.13 0.40 0.75 0.51 0.39 19
Strukture of activity spaces Criteria: Share of trips to most visited locations Cluster 20
Share of most important destinations of all trips (Mobidrive) 50 100 40 80 30 60 Schönfelder und Axhausen, 2004 [%] 20 10 0 1 2 3 4 5 6 7 8 9 10 Mean share Cumulative share 40 20 0 [%] 21
Distribution of activity clusters number (All trips) 60% 40% 20% Schönfelder und Axhausen, 2004 0% 1 2 3 4 5 Uppsala (144) Mobidrive (317) SVI Stabilität (230) Cluster: 1 km radius; minimum 3 unique locations and 10% of all trips 22
Distribution of activity clusters number (car drivers) 80% 60% 40% 20% Schönfelder und Axhausen, 2004 0% 1 2 3 4 5 Mobidrive car only (197) SVI Stabilität car only (187) Uppsala car only (75) Borlänge (67) Copenhagen (50) Cluster: 1 km radius; 3 unique locations and 10% of all car trips 23
24 Centre of clusters: Activity purposes 2 2 0 0 1 0 Other 0 0 4 4 0 1 Work related 3 2 4 4 1 1 Pick/Drop 0 1 1 0 1 1 Long-term shopping 1 2 1 3 0 5 Private business 12 19 5 9 4 6 Grocery 1 0 11 8 1 8 School 25 18 22 15 24 11 Work 12 12 10 14 11 12 Leisure 44 44 42 43 57 55 Home Fulltime Uppsala All Fulltime Thurgau All Fulltime Mobi All Purpose Schönfelder und Axhausen, 2004
Innovation in destination choice Two types of observation: New locations over the reporting / monitoring period Locations visited for the first time 25
New locations Schönfelder und Axhausen, 2004 Number of new locations/day [n] 3 2,5 2 1,5 1 0,5 0 Borlänge; car trips, all puroses Copenhagen; car trips, all purposes Uppsala; all purposes Thurgau; all purposes Mobidrive; all purposes 12 week leisure study; leisure only 0 10 20 30 40 50 60 70 Week of reporting period 26
Places visited for the first time (Thurgau 2003) 2 1,5 Often Never and seldom visited before: all Never and seldom visited before: leisure 1 Schönfelder und Axhausen, 2004 0,5 0 Mo Mo Mo Mo Mo Mo First time or never before less than 4 visits Often: 4 to 10 visits 27
Summary Activity spaces are measurable The relationship between number of trips and number of unique locations seems constant AS has a structure with few clusters The set of known places increases permanently The rate of innovation is constant The size of activity spaces is temporarily not or only partly stable 28
Appendix: Measuring activity spaces (Part 2) 29
Approach 2: Kernel densities Density surface created by distribution of locations weighted by frequency of visit Measure: Area with positive density value Focus: Clustering 30
Example: Zürich s commuter shed 2000 31
Approach 3: Shortest path network Smallest geometry based on all O-Drelations observed (e.g. shortest paths) Measure: Length of geometry / area spanned / buffered area Focus: Spread of locations 32
Obvious refinements All: Segmentation by type of interaction; time period Appropriate weighting schemes (ln?) Confidence ellipse, Kernel densities: Removal of a-priori excluded spaces Shortest path networks: Use mode-specific networks Use stochastic assignment 33
Refinement: Exclusion of excluded areas 34
Additional information Confidence ellipse: Angle of the main axis relative to reference point Mean vector between point of interaction and base Kernel densities: Number of contiguous areas (clusters) Shortest path networks: All descriptive statistics for network graphs Flow estimates 35
Additional information: Flow estimates 36
Literature and references Axhausen, K.W. (2003) Social networks and travel: Some hypotheses, Arbeitsberichte Verkehr- und Raumplanung, 197, Institut für Verkehrsplanung und Transportsysteme (IVT), ETH Zürich, Zürich. Axhausen, K.W. und P. Fröhlich (2004) Public investment and accessibility change, in P. Marti und A. Müller (Hrsg.) Festschrift Schalcher, vdf, Zürich. Botte, M. (2003) Strukturen des Pendelns in der Schweiz, Diplomarbeit, Fakultät für Bauingenieurwesen, TU Dresden, August 2003. Putnam, R.D. (1999) Bowling Alone: The collapse and revival of American community, Schuster and Schuster, New York. Schönfelder, S. and K.W. Axhausen (2004) Structure and innovation of human activity spaces, Arbeitsberichte Verkehrs- und Raumplanung, 258, IVT, ETH Zürich, Zürich. Schönfelder, S. and K.W. Axhausen (2003) On the variability of human activity spaces, in M. Koll-Schretzenmayr, M. Keiner und G. Nussbaumer (eds.) The Real and Virtual Worlds of Spatial Planning, 237-262, Springer, Heidelberg. Tschopp, M., R. Sieber, P. Keller und K.W. Axhausen (2003) Demographie und Raum in der Schweiz, DISP, 153, 25-32. 37