Evaluating Place-based Accessibility using Space-time Utility Perspective

Transcription

1 Proceedngs of the 3rd Internatonal Conference on Cvl, Structural and Transportaton Engneerng (ICCSTE'18) Nagara Falls, Canada June 10 12, 2018 Paper No. 109 DOI: /ccste Evaluatng Place-based Accessblty usng Space-tme Utlty Perspectve Wllam H. K. Lam 1, B Yu Chen 1,2, Erc J. Mller 3 1 Department of Cvl and Envronmental Engneerng, the Hong Kong Polytechnc Unversty Hong Kong, Chna wllam.lam@polyu.edu.hk 2 State Key Laboratory of Informaton Engneerng n Surveyng, Mappng and Remote Sensng, Wuhan Unversty Wuhan, Chna chen.byu@whu.edu.cn 3 Department of Cvl Engneerng, Unversty of Toronto Toronto, Canada mller@ecf.utoronto.ca Abstract The conventonal statc place-based accessblty measures are commonly used n practce for evaluaton of transport network performance. However, ths conventonal approach have often been crtczed for gnorng the dynamcs n human space-tme behavours and urban envronments. In ths study, dynamc place-based accessblty measures are proposed to extend the conventonal place-based measures by combnng the merts of the place-based and space-tme utlty-based approaches. In ths new approach, the accessblty of a place wthn the study area can be evaluated by the space-tme utlty approach n terms of actvty duraton, travel tme and faclty attractveness. The ndvdual choce behavours amongst multple alternatves are explctly consdered n the placebased accessblty evaluaton. To demonstrate the mplementaton and applcablty of the proposed place-based accessblty measures, a comprehensve case study s carred out n Wuhan whch s one of the fast-growng mega ctes n Chna. Keywords: Accessblty, Space-Tme Utlty, Tme Geography, Transport Network Performance. 1. Introducton Accessblty s an mportant concept for urban plannng, transport geography, and other related felds. It s defned as the ease wth whch urban servces can be reached from a partcular place or locaton (or by ndvduals at that locaton) usng a partcular transport system [1-2]. Poor accessblty to urban servces (e.g., obs, recreatonal servces, healthcare facltes, etc.) can negatvely mpact the ctzens qualty of lfe, and even lead to socal exclusons n extreme cases. Accessblty to urban servces has been ntensvely studed n the lterature not only for varous strategc plannng purposes (e.g., transport network performance evaluaton) [3-5], but also for beng an explanatory factor n many geographc phenomena analyss (e.g., socal equty and ustce) [6-8]. The evaluaton of accessblty to urban servces depends on accessblty measures. In the lterature, varous measures have been developed and can be roughly classfed nto two categores, ncludng place-based and ndvdual-based measures [2, 9]. Conventonal place-based measures conceptualzed accessblty largely n terms of the proxmty to urban servces from an ndvdual s resdental locaton. The wdely used place-based measures nclude the travel dstance to the nearest servce locaton, the cumulatve number of servces wthn a specfed cut-off dstance, gravty-type measures n whch the attractveness of servces decreases wth the dstance from the orgn [10, 11]. These conventonal place-based measures requred a few of aggregated data and can be easly appled for large-scale study areas. However, they are statc spatal terms and often crtczed for gnorance of dynamcs n human space-tme behavours and urban envronments [9, 11, 12]. In the past decade, t has become easer to move beyond the place-based accessblty measures due to the avalablty of ndvdual-level actvty dary data [2, 9, 12]. In the lterature, several ndvdual-based (or space-tme) measures have been proposed. Most of them are bult on the tme geographc framework [13] for capturng complextes of ndvdual actvty-travel behavours under varous space-tme constrants. The number of reachable urban servces and the 109-1

2 cumulatve actvty duratons at reachable urban servces are two well-known ndvdual-based measures [10]. Theoretcally, a better approach s the space-tme utlty measures that can drectly evaluate ndvdual utltes of actvty partcpaton n terms of actvty duraton, travel cost and the faclty attractveness [14]. The ndvdual choce behavours amongst multple alternatves, such as logsum, can be explctly consdered. Several advantages of usng space-tme utlty approach, partcularly log-sum, for the ndvdual accessblty evaluaton are dscussed and summarzed n [15]. All these ndvdual-based measures are well suted to evaluate accessblty to urban servces for people n dfferent socal groups and geographcal regons [1]. However, they requre detaled ndvdual-level actvty dary data, whch can be very expensve and dffcult to acqure large number of samples. As a result, prevous studes used ndvdual-based measures are restrcted to a relatvely small area usng a few samples. In recent years, ncreasng attenton has been gven to mprove the conventonal place-based measures wth ndvdualbased perspectves. Páez et al. [16] mproved conventonal cumulatve-opportunty measure by usng model estmated average travelled dstance of people n dfferent socal groups and geographcal regons. Delafontane et al. [17] proposed enhanced place-based measures by consderng the faclty s openng hours and actvty duratons at facltes. Wdener et al. [18] and Fransen et al. [19] extended conventonal place-based measures by usng nteracton potental metrcs wth consderaton of nter-zonal commutng patterns. In vew of ths trend, ths study ams to develop a dynamc operatonal accessblty evaluaton framework wth ntegraton of the advantages of both the place-based and space-tme utlty-based approaches. In ths study, the accessblty of a locaton s evaluated by the space-tme utlty approach n terms of actvty duraton, travel tme and faclty attractveness. The ndvdual choce behavours amongst multple alternatves are explctly consdered n the place-based accessblty evaluaton. Therefore, the proposed place-based utlty measures can enhance the ablty to realstcally evaluate place-based accessblty by usng the robust space-tme utlty approach. To demonstrate the operatonalzaton and applcablty of the proposed place-based utlty measures, a comprehensve case study s conducted n Wuhan whch s one of the mega ctes n Chna. Two types of spatotemporal bg data, ncludng check-n data and tax trackng data, are collected for case study. Check-n data of a popular socal meda ste are extracted to estmate the tmedependent attractveness functon of facltes. Large-scale tax trackng data are collected to estmate tme-varyng travel tmes n Wuhan road network. The results of the case study ndcate that the proposed place-based utlty measures can full capture the temporal varatons of place-based accessblty due to both tme-varyng travel tmes and attractveness of facltes. The results of the case study also demonstrate the potental usefulness of mergng spatotemporal bg data for large-scale accessblty studes. The remander of ths paper s structured as follows. In the next secton, the conventonal place-based accessblty measures are brefly ntroduced to provde the background of the problem. The proposed place-based utlty measures are then presented n Secton 3. The case study n Wuhan s reported n Secton 4. Fnally, conclusons are gven n Secton 5 together wth recommendaton for further studes. 2. Conventonal Place-Based Accessblty Measures Accessblty has tradtonally been evaluated by place-based accessblty measures. For nstance, the wdely used cumulatve-opportunty measure [20], denoted by CUM, s represented by the number of facltes wthn the standard travel tme polygon (TTP). As llustrated n Fgure 1, TTP delmts all possble geographcal locatons, where the travel tme from the ndvdual s resdental locaton r s less than gven travel tme budget b. It can be expressed as TTP { x t b} (1) rx where t rx s the travel tme from an ndvdual s resdental locaton r to locaton x. Let f be a faclty for conductng actvty. The set of facltes wthn the TTP forms the choce set FOS { f TTP}. Then, the CUM measure for actvty can be expressed as CUM ( ) 1 (2) f FOS 109-2

3 Another commonly used place-based accessblty measure s the followng gravty-type measure (denoted by GRAV ): where a s attractveness of faclty f f rf GRAV ( ) a exp t (3) f FOS f, t s the travel tme from resdental locaton r to faclty rf f. Attractveness a s measured by a multtude of attrbutes related to the faclty, such as sze, servces offered, watng tmes, etc. f Senstve parameters, and, are related to attractveness and the frcton of dstance to the faclty for conductng actvty, respectvely. Comparng wth CUM (), ths GRAV ( ) measure ncorporates two addtonal components: the faclty attractveness and the frcton of dstance to the faclty, expressed by the dstance-decay functon. A negatve exponental decay functon s dscussed here, because ths s one of the most wdely used dstance-decay functons n the accessblty lterature. For the use of other functons, nterested readers may refer to [10]. Although these place-based measures are valuable for evaluatng accessblty of large-scale study areas, they are often crtczed for ther gnorance of dynamcs n human space-tme behavours and urban envronments. In next secton, these conventonal place-based measures are mproved by ncorporatng the tme dmenson, n terms of actvty duratons and accessblty temporal varaton at dfferent tmes of the day. Fg. 1: Standard travel tme polygon concept. 3. Proposed Place-Based Space-Tme Utlty Measures Followng the tme geographc approach, gven an ndvdual lvng at resdental locaton r, wth a tme budget from t r to t s, all possble space-tme locatons for the ndvdual s actvty partcpatons can be expressed as the forward spacetme cone, FC() t, (Mller, 2005): FC( t) x t t t, t t t c, t t t (4) r rx rx s r mn r s where t rx s the travel tme from resdental locaton r to locaton x ; and c mn s the mnmum actvty duraton requred for actvty partcpatons. Fgure 2 llustrates ths space-tme cone concept n three-dmensonal (3D) space. The heght of space-tme cone at locaton x ndcates the maxmum duraton c x for actvty partcpatons at the locaton, whch can be wrtten as: 109-3

4 cx ts tr trx (5) To successfully partcpate n actvty at the locaton, the maxmum duraton should satsfy the cx cmn constrant. The proecton of space-tme cone onto the two-dmensonal (2D) geographcal space s the potental path area, whch s essentally dentcal to the standard travel tme polygon: TTP { x t t t c b} (6) rx s r where travel tme budget b ts tr cmn. Therefore, FC() t shown n Fgure 2 extends TTP shown n Fgure 1 by ncorporatng the tme dmenson n terms of actvty duratons; and FOS defned by FC s dentcal to that defned by the above TTP. mn Fg. 2: Forward space-tme cone concept. Followng the space-tme utlty approach [14], gven a faclty f FOS partcpatons at the faclty can be measured n terms of attractveness of the faclty duraton c as: f, the drect benefts (or utlty) of actvty a, travel tme t and actvty U ( ) a c exp t (7) f f f rf where, and are senstve parameters related to attractveness, actvty duraton and travel tme on the space-tme utlty. Three place-tme space-tme accessblty measures are then developed to evaluate the accessblty of ndvduals lvng at locaton. In the urban envronment, a locaton may be covered by servce areas of several facltes that provde the same types of actvty. It should be noted that varous szes of servce areas can be used for dfferent facltes. These facltes consttute the faclty choce set for an ndvdual s actvty partcpatons, denoted by F { f1,..., fn}. The frst place-based space-tme accessblty measure, denoted by CWA(), adopts the consumer welfare aggregaton (CWA) prncple used n the conventonal place-based accessblty measures. It s the summaton of actvty utltes provded by all facltes n the choce set F : f rf CWA( ) U f ( ) f F (8) 109-4

5 where U f () s the utlty derved from actvty partcpaton at faclty f F defned n Eq. (6). Ths accessblty measure represents all possble actvty utltes (welfares) enoyed by an ndvdual at locaton. In addton to the CWA prncple, consumer welfare maxmzaton (CWM) prncple and random utlty maxmzaton (RUM) prncple used n the space-tme utlty accessblty approach [14] are adopted. The second place-based space-tme accessblty measure, denoted by CWM (), follows the CWM prncple. Assumng the ndvdual s a ratonal utlty maxmzer, he/she chooses only one faclty f F whch provdes the maxmum actvty utlty for performng actvtes. Accordngly, the accessblty of ndvduals at locaton s measured as the maxmum utlty provded by a partcular faclty f F : CWM ( ) max U ( ) (9) f { ff } The thrd place-based space-tme accessblty measure, denoted by RUM (), adopts the RUM prncple. Compared to the CWM prncple, the RUM prncple bulds on the random utlty theory, addng an unobservable random error component nto the actvty utlty measure,.e., Eq. (6). The error component of all facltes f F are assumed to follow ndependently and dentcally dstrbuted Gumbel dstrbutons. Accordngly, the mechansm of choosng a faclty to maxmze actvty utltes can be formulated as a logt dscrete choce model. Accessblty based on the RUM prncple s therefore expressed as followng logsum accessblty measure [15]: 1 RUM ( ) ln exp U f ( ) f F (10) Unlke CWM (), ths RUM () measure s a summary ndcator representng the expected maxmum utlty of the full faclty choce set. 4. Case Study Ths secton presents a case study usng real-world data collected n Wuhan whch s one of the fast growng mega ctes n Chna. Ths case study ams to demonstrate the applcablty of the proposed accessblty evaluaton framework. The case study s concerned wth the accessblty to food servce facltes n Wuhan. The data collected n ths case study ncluded a detaled dgtal road network, a large-scale tax trackng data set for estmatng travel tme dstrbutons, and nformaton about dnng facltes extracted from an onlne socal meda applcaton. As shown n Fgure 3, the Wuhan road network conssted of 19,306 nodes and 46,757 lnks. Real-world floatng car data (FCD) was collected on a typcal Thursday (September 3, 2009) to estmate traffc condtons of the Wuhan road network. The detaled method for estmatng traffc condtons of Wuhan road network s documented n [21]. As shown, lnks shown n red represent congested lnks (< 20 km/h); yellow represents slghtly congested lnks (20 40 km/h); and green represents uncongested lnks (> 40 km/h). The fgure shows that 9.7% of lnks n the Wuhan network were congested, mostly around seven commercal centres

6 Fg. 3: Traffc condton of Wuhan network. Fg. 4: Spatal dstrbuton of food servce facltes. Data on food servce facltes n Wuhan was collected from a locaton-based socal networkng webste n Chna, named Jepang ( Jepang, launched n 2010, s a popular web and moble applcaton, wth fve mllon users. In ths study, 4,407 food servce facltes were collected n September The spatal dstrbuton of food servce facltes s llustrated n Fgure 4, whch shows that dnng facltes are not evenly dstrbuted n the cty but rather clustered at sx commercal centres, especally n the Wuguang area. Place-based space-tme accessblty to food servce facltes n Wuhan Cty was evaluated usng the RUM prncple,.e., RUM () defned n Eq. (10), for llustraton. Fgure 5 shows the resultng accessblty durng the evenng peak hour (6 p.m. 7 p.m.). As shown, the accessblty to dnng facltes was not evenly dstrbuted n Wuhan Cty. Compared to suburban areas, the values of RUM () were relatvely hgh (over 300) n seven commercal centres. The Wuguang area had the hghest value of RUM () (over 800) due to ts large number of food servce facltes. Therefore, the proposed space-tme accessblty measures can well represent the spatal heterogenety of food servce accessblty n Wuhan cty

7 Fg. 5: Spatal dstrbuton of accessblty to food servce facltes n Wuhan cty. 5. Concluson Ths study proposed new place-based accessblty measures wth consderaton of space-tme effects for evaluatng accessblty n large-scale study areas. The proposed framework reconcles conventonal place-based accessblty measures wth space-tme utlty approach. The accessblty of a locaton was measured wth respect to actvty duraton, travel tme and faclty attractveness. The ndvdual choce behavours amongst multple alternatves are also explctly consdered by usng three prncples, ncludng consumer welfare aggregaton prncple, consumer welfare maxmzaton prncple, and random utlty maxmzaton prncple. To demonstrate the operatonalzaton and applcablty of the proposed place-based utlty measures, a comprehensve case study s carred out n a mega cty n Chna. The case study results ndcated that the proposed space-tme accessblty measures can ncorporate tme dmenson nto the place-based accessblty, n terms of actvty duraton and tme-dependent traffc condtons. Several drectons for future research are worth notng. Frstly, the proposed accessblty measures are confned to prvate car mode only. The extenson of the proposed accessblty evaluaton framework to mult-modal networks s an nterestng topc for fast-growng mega ctes n Chna and Asa. Secondly, the accessblty to food servces was examned manly based on restaurants and other dnng facltes. It s nterestng to apply the proposed framework for evaluatng accessblty to other types of urban opportuntes, such as ob and healthcare servces. Last but not the least, the mpacts of ntellgent transport systems on the accessblty to urban servces should also be further nvestgated. Acknowledgements The work descrbed n ths paper was ontly supported by the Research Grants Councl of the Hong Kong Specal Admnstratve Regon, Chna (No. PolyU /17E), the Research Insttute for Sustanable Urban Development and Research Commttee of the Hong Kong Polytechnc Unversty (1-ZVEW and 4-ZZFY). References [1] M.-P. Kwan, and J. Weber, Scale and accessblty: Implcatons for the analyss of land use-travel nteracton, Appled Geography, vol. 28, no. 2, pp , [2] K. T. Geurs, and B. van Wee, Accessblty evaluaton of land-use and transport strateges: revew and research drectons, Journal of Transport Geography, vol. 12, no. 2, pp , [3] F. Lao, and B. van Wee, Accessblty measures for robustness of the transport system, Transportaton, vol. 44, no. 5, pp , [4] K. Lucas, B. van Wee, and K. Maat, A method to evaluate equtable accessblty: combnng ethcal theores and accessblty-based approaches, Transportaton, vol. 43, no. 3, pp ,

8 [5] W. Yang, B. Y. Chen, X. Cao et al., The spatal characterstcs and nfluencng factors of modal accessblty gaps: A case study for Guangzhou, Chna, Journal of Transport Geography, vol. 60, pp , [6] D. W. S. Wong, and S. L. Shaw, Measurng segregaton: an actvty space approach, Journal of Geographcal Systems, vol. 13, no. 2, pp , Jun [7] B. Y. Chen, Y. Wang, D. Wang et al., Understandng the mpacts of human moblty on accessblty usng massve moble phone trackng data, Annals of the Amercan Assocaton of Geographers, DOI: / , [8] S. Slm, and R. Ahas, Ethnc dfferences n actvty spaces: A study of out-of-home nonemployment actvtes wth moble phone data, Annals of the Assocaton of Amercan Geographers, vol. 104, no. 3, pp , May 4, [9] M.-P. Kwan, and J. Weber, Indvdual accessblty revsted: Implcatons for geographcal analyss n the twentyfrst Century, Geographcal Analyss, vol. 35, no. 4, pp , [10] M. P. Kwan, Space-tme and ntegral measures of ndvdual accessblty: A comparatve analyss usng a pontbased framework, Geographcal Analyss, vol. 30, no. 3, pp , Jul, [11] T. Neutens, T. Schwanen, F. Wtlox et al., Equty of urban servce delvery: a comparson of dfferent accessblty measures, Envronment and Plannng A, vol. 42, no. 7, pp , Jul, [12] H. J. Mller, Place-based versus people-based geographc nformaton scence, Geography Compass, vol. 1, no. 3, pp , [13] T. Hägerstrand, What about people n regonal scence?, Papers n Regonal Scence, vol. 24, no. 1, pp. 7-24, [14] H. J. Mller, Measurng space-tme accessblty benefts wthn transportaton networks: Basc theory and computatonal procedures, Geographcal Analyss, vol. 31, no. 2, pp , Apr, [15] B. van Wee, Accessble accessblty research challenges, Journal of Transport Geography, vol. 51, pp. 9-16, [16] A. Páez, R. G. Mercado, S. Farber et al., Relatve accessblty deprvaton ndcators for urban settngs: Defntons and applcaton to food deserts n Montreal, Urban Studes, vol. 47, no. 7, pp , [17] M. Delafontane, T. Neutens, and N. V. d. Weghe, A GIS toolkt for measurng and mappng space tme accessblty from a place-based perspectve, Internatonal Journal of Geographcal Informaton Scence, vol. 26, no. 6, pp , [18] M. J. Wdener, S. Farber, T. Neutens et al., Usng urban commutng data to calculate a spatotemporal accessblty measure for food envronment studes, Health & Place, vol. 21, pp. 1-9, [19] K. Fransen, T. Neutens, S. Farber et al., Identfyng publc transport gaps usng tme-dependent accessblty levels, Journal of Transport Geography, vol. 48, pp , Oct, [20] M. J. Breheny, The measurement of spatal opportunty n strategc plannng, Regonal Studes, vol. 12, no. 4, pp , [21] B. Y. Chen, C. Sh, J. Zhang et al., Most relable path-fndng algorthm for maxmzng on-tme arrval probablty, Transportmetrca B, vol. 5, no. 3, pp ,