This article was downloaded by: [176.9.124.142] Publisher: Routledge
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This article was downloaded by: [176.9.124.142] Publisher: Routledge
This article was downloaded by: [176.9.124.142] On: 19 September 2014, At: 01:28 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Transportation Planning and Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gtpt20 How to Incorporate the Spatial Dimension in Destination Choice Models: The Case of Antwerp a Hakim Hammadou , Isabelle Thomas d Verhetsel & Frank Witlox a b c , Ann e a Department of Geography , Université Catholique de Louvain , Louvain-la-Neuve, Belgium b Centre of Operational Research and Econometrics (CORE) , Louvain-la-Neuve, Belgium c National Fund for Scientific Research , Brussels, Belgium d Department of Transport and Regional Economics , University of Antwerp , Belgium e Department of Geography , Ghent University , Belgium Published online: 13 Mar 2008. To cite this article: Hakim Hammadou , Isabelle Thomas , Ann Verhetsel & Frank Witlox (2008) How to Incorporate the Spatial Dimension in Destination Choice Models: The Case of Antwerp, Transportation Planning and Technology, 31:2, 153-181, DOI: 10.1080/03081060801948126 To link to this article: http://dx.doi.org/10.1080/03081060801948126 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. 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Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions Transportation Planning and Technology, April 2008 Vol. 31, No. 2, pp. 153181 ARTICLE Downloaded by [176.9.124.142] at 01:28 19 September 2014 How to Incorporate the Spatial Dimension in Destination Choice Models: The Case of Antwerp HAKIM HAMMADOU*, ISABELLE THOMAS*,**,$, ANN VERHETSEL$$ & FRANK WITLOX§ *Department of Geography, Universite´ Catholique de Louvain, Louvain-la-Neuve, Belgium; **Centre of Operational Research and Econometrics (CORE), Louvain-laNeuve, Belgium; $National Fund for Scientific Research, Brussels, Belgium; $$Department of Transport and Regional Economics, University of Antwerp, Belgium & §Department of Geography, Ghent University, Belgium (Received 3 May 2006; Revised 10 January 2008; In final form 17 January 2008) ABSTRACT This paper presents and estimates destination choice models based on a large sample of intra-urban trips. Particular attention is paid to incorporating the effects of the spatial dimension. The data used relate to non-work trips in the agglomeration of Antwerp (Belgium). A geographical analysis is performed in order to represent the city and its suburbs by a limited set of zones of destinations and to characterize these zones in terms of land use. Different types of discrete choice model are compared in terms of utility function, global formulation and performance. The mixed nested logit formulation with random coefficients appears to be the most attractive. The results confirm the difficulty of grasping spatial realities by simple quantitative measurements but also illustrate the importance of ‘space’ when choosing a destination. The empirical results also show that land use and urban development policies clearly have their effect on urban mobility. KEY WORDS: Destination choice model; mixed nested logit; trip-based approach; land use; urban mobility; Antwerp Correspondence Address: Frank Witlox, Department of Geography, Ghent University, Belgium. Email: [email protected] ISSN 0308-1060 print: ISSN 1029-0354 online # 2008 Taylor & Francis DOI: 10.1080/03081060801948126 154 H. Hammadou et al. Downloaded by [176.9.124.142] at 01:28 19 September 2014 Introduction Travel demand analysis is intrinsically spatial: the spatial separation of activities is indeed the essence of travel demand. Although this assertion is self-evident, in travel analysis and even more in travel behaviour modelling, the incorporation of the effects of the spatial distribution of activity-based travel has only recently been taken explicitly into account. Important contributions in this respect are by Dijst and Vidakovic (1997), Badoe and Miller (2000), Ewing and Cervero (2001), Stead (2001), Bhat and Zhao (2002), Kitamura (2004) and Handy et al. (2005). In each case an attempt was made to sort out the extent to which the characteristics of the built environment and land use have an impact on travel behaviour. The present paper sets out to achieve an identical goal. It aims at representing, modelling and understanding travel behaviour and destination choices, but differs from previous analyses in a number of aspects: (i) the number of so-called spatial variables is extended; (ii) different types of destination choice models are being compared; (iii) use is made of activity-based data (instead of crosssectional data); and (iv) the emphasis is on explaining destination choice (instead of trip length, trip frequency, or modal choice). First, our paper attempts to incorporate a ‘real’ value of space in destination choice models. Given that there is no unique measurement that summarizes the complexity of space this is a truly challenging effort. Unlike Dijst and Vidakovic (1997), for instance, who focus on people’s action space within a city using only the spatial variable ‘distance between locations of activity bases’, we assume, like Handy et al. (2005) that the choice of destination depends upon the characteristics of the zones (i.e. the built environment, land use, neighbourhood characteristics) as well as of the travellers (socio-economic characteristics, attitudes). Therefore, it is necessary to have information on attributes of the zones and data on individual and household characteristics. With respect to the former, geographical information systems (GIS) techniques can be used in order to provide information on land use, density characteristics and accessibility of each zone (Slavin, 2004). Second, an important problem in destination choice modelling relates to the modelling approach itself. Statistical theory and methods often assume independent observations, but due to spatial dependence this condition is rarely met when analysing spatial data (Miller, 1999). As a result, the nature of spatial data conditions the model structure. Our search for the most appropriate modelling procedure consists of two steps: first, the performance of two types of discrete choice model structures is tested: the multinomial logit (MNL) and the nested logit. Second, the most convincing form of the utility function must be defined. Related to the selection of the choice model, is the issue of how Downloaded by [176.9.124.142] at 01:28 19 September 2014 Destination Choice Models 155 to deal with a very large number of spatial choice alternatives. BenAkiva and Lerman (1985) suggested to use a restricted set of alternatives rather than a full set. In this paper, however, the study area is divided into a limited number of zones (33 in all) representing the alternative areas of destination. There is no sampling: the total set of spatial destination alternatives for each individual is considered, but aggregated into zones. The number of zones is large enough for representing reasonably well the urban reality, and small enough to comprehend spatial patterns. The model based on spatially aggregated data is also compared to a disaggregated formulation. Third, given the need to have information on attributes of the zones as well as on individual and household characteristics, we opt to use to work with trip chaining data. The data used stem from individual travel surveys describing daily activities (about 30,000 trips collected in 1999) in the city region of Antwerp (Belgium). Fourth, and finally, the objective of the current paper is on explaining destination choice and not, for example, modal choice. Hence, an intrinsic spatial variable is used as target or dependent variable. The results of the spatial model to be developed are to give an insight into the factors that explain the respondent’s probability to choose a certain destination within a set of destination zones, contributing to a better understanding of travel behaviour. This paper is structured as follows. Section ‘Methodology and Data Requirements’ is dedicated to the discussion of the methodological framework and the specific data requirements, including model specification and estimation procedure, defining the study area and the destination zones, introducing the travel data, and discussing the construction of the spatial variables (land use, density and accessibility). In Section ‘Results’ the estimation results of the destination choice models are presented. Finally, in Section ‘Conclusions and Future Research’, conclusions and research perspectives are reported. Methodology and Data Requirements If we want to explain the way in which people choose among different destination zones, we need to choose a method and a model as well as an adequate set of data. With respect to the model specification it is common sense to advance a discrete choice model. However, given the large number of model possibilities, specific attention is paid to the econometric model structure (i.e. the type of choice model) and the functional form (i.e. the type of utility function). The data requirements refer to the issue of the definition of the destination zones and the selection and construction of the geographical variables. 156 H. Hammadou et al. Downloaded by [176.9.124.142] at 01:28 19 September 2014 Model Specification and Estimation Procedure Modelling destination choices implies using and selecting a discrete choice model. Discrete choice models assume that the overall utility of a choice alternative is composed of a fixed (i.e. systematic or deterministic) utility value and a random or error utility component. Depending on the assumptions made regarding the distribution of the error terms, several discrete choice model structures have been developed in the literature (Domencich & McFadden, 1975; Hensher & Johnson, 1981a; Cascetta, 2001; Train, 2003; Quinet & Vickerman, 2004). Logit is by far the most widely used discrete choice model. It is derived under the assumption that the random utility elements are independently and identically distributed (IID) (McFadden, 1973, 1976). In other words, it is assumed that the unobserved factors are uncorrelated over the choice alternatives, and have the same variance for all alternatives. If IID can be defended, the Type I extreme value distribution seems the most suitable distribution (Johnson & Kotz, 1970), resulting in the well-known MNL model (Cramer, 1991; Ortuzar & Willumsen, 2001). It is true that logit models have a strong theoretical base, a simple mathematical structure, and are quite easy to estimate. Their popularity is due to this convenience. However, given the restrictive assumption that a MNL model can only be applied to situations in which alternatives are totally independent, and that this is certainly not the case for spatial alternatives (our concern), the use of a simple MNL model seems inappropriate. A common solution to relaxing the assumptions of independence among alternatives is to introduce a nested model structure (Koppelman & Sethi, 2000; Papola, 2004). In such a nested logit model, choice alternatives are segmented and structured in branches or nests that are more similar (Suarez et al., 2004). Indeed, if the destination choice process is hierarchical and similar alternatives are grouped into the same branches of the choice hierarchy, then alternatives within each branch are more likely to follow the IID assumption. In the present paper, destinations will be grouped according to urban level (subregions mentioned in Section ‘Studied Area and Defining Destination Zones’ and defined by Van der Haegen et al., 1996). This means that each individual is assumed to first choose an urban level (e.g. urban versus suburban) and then, within that broad spatial zone, to choose a precise destination. The result is a nested logit formulation with two levels of decision for destination (Figure 1). The mathematical formulation of the nested logit with two levels of decision can be briefly described as follows. We assume that the utility function of the destination choice j can be split into one part that characterizes the urban level (Vl) and another part that varies with the choice within that level (Vj(l)) Destination Choice Models 157 Downloaded by [176.9.124.142] at 01:28 19 September 2014 Origin Urban level l = 1,…,4 City centre l=1 19th century area l=2 Destination j = 1,…, 33 Dest j= 1 ,.., 5 Dest j = 1 Suburbs l=3 Dest j = 1,…, 21 Urban fringe l=4 Dest j = 1, …, 6 Figure 1. Decision-making structure according to the nested logit model developed in this paper Uij Vl Vj(l) o j (1) where oj is the stochastic part of the utility (error term). We assume that the individual specific error terms o1, o2,. . .,oj are random and IID distributed. Hence, the probability that an individual chooses a destination j is given by ll 1 PJl exp(Vj =ll ) exp(V =l ) j(l) l j1 P(j) (2) PL PJl exp(V =l ) j(l) l j1 l1 which corresponds to a nested logit formulation with two levels of decision for destination. The parameter ll is a measure of the degree of independence in unobserved utility among the alternatives within urban subregion l. Its value must be between zero and one for the model to be consistent with utility maximization behaviour for all possible values of the explanatory variables (Train, 2003; Bhat & Guo, 2004). The nested logit is appealing in terms of its ability to accommodate differential degrees of interdependence (i.e. similarity) between subsets of alternatives in a choice set (Hensher & Greene, 2002), but many published applications display a lack of attention to the very precise form that these models must take to ensure that the resulting model is consistent with utility maximization. Thus, next to the assumptions regarding the unobserved utility components that lead to different econometric model structures, we also have to focus on the functional form of the utility function. In its usual form the utility function of a discrete choice model is given by Uij Vijoij where Vij is the deterministic part of the utility and oij the Downloaded by [176.9.124.142] at 01:28 19 September 2014 158 H. Hammadou et al. random unobserved component of the utility. The deterministic term is usually specified as a linear function of the attributes of the alternative and the characteristics of the decision-maker, and is denoted by ak bjk Xijk o ij where bjk is the coefficient for attribute k of alternative j, and Xijk is a vector of observable attribute values. Although a linear function of the parameters is most commonly applied, it is not always the most accurate representation. Therefore, two alternatives for the linear utility function are considered here: BoxCox transformation and random coefficients. If a BoxCox transformation (c.f. Gaudry & Dagenais, 1979; Picard & Gaudry, 1998; Hensher & Johnson, 1981b) is done, it can be shown that the regression residuals are usually more homoscedastic and closer to a normal distribution. Just as for models with linear utility functions, models with BoxCox transformation also assume that the coefficients are constant (fixed for all individuals): the explanatory variables have the same effect for each individual. However, the population is in general rather heterogeneous and the effect of each explanatory variable can vary from one individual to another. In order to account for this characteristic the b-coefficients should be allowed to vary randomly instead of being fixed over the decisionmakers. The result is a so-called model with random coefficients, which accounts for the heterogeneity in the population. The functional form of the utility function is then somewhat different (Train & McFadden, 2000). The utility is Unj b?nk Xnjk o nj ; where b?n is the vector of coefficients for decision-maker n representing that person’s characteristics. Suppose b?n is normally distributed in the population with mean b and covariance W:b?n N(b; W): The goal of the research is to estimate the parameters b and W (Train, 2003, p. 111). Assessment of what type of utility function specification should be used depends on the choice problem being analysed. In Section ‘Determining the Functional Form’ this is discussed in more detail. Studied Area and Defining Destination Zones The area studied in this paper is that of metropolitan Antwerp. Antwerp is the second largest city of Belgium, located in the northern part of the country, close to the border with The Netherlands. It has approximately 500,000 inhabitants and is characterized by a large harbour bound to the North Sea by the river Scheldt. As in most cases, the city sprawls far away from its historical centre. We here consider the city region from centre to periphery: the city centre, the 19th century centre (core), the suburbs and the urban fringe. These subregions were defined independently by means of morphological and socio-economic variables (Van der Haegen et al., 1996). In a former paper, we showed that the friction of distance (distance decay) is different in each of these subregions Downloaded by [176.9.124.142] at 01:28 19 September 2014 Destination Choice Models 159 (Hammadou et al., 2003). The city region consists of 608 statistical sectors (also called neighbourhoods or wards equivalent to 32 zip codes and 18 communes) (Figure 2). Clearly, as also pointed out by Ben-Akiva and Lerman (1985), modelling destination choices at a ward level is quite difficult: the number of spatial alternatives is too high (in our case N 608) and wards vary in size and shape. In order to solve this problem we aggregated the 608 statistical sectors into a smaller, more workable number of zones (Figures 3 and 4). As in most quantitative geographical analyses (Openshaw & Taylor, 1979), spatial aggregation also substantially affects travel demand modelling results. Miller (2004) mentioned some major spatial analytical issues related to zoning: spatial dependency, spatial heterogeneity, boundary problems and scale effects. Unfortunately, there is no predefined method for aggregation in order to avoid these analytical pitfalls. In our approach we attempt to tackle the spatial aggregation problem by constructing a so-called zoning algorithm that aims at reducing the number of destinations by maximizing internal homogeneity and external heterogeneity of the aggregated zones. By aggregating places, we want to better control the main spatial trends and avoid ‘noise’ in the spatial model. Methodological details about the zoning algorithm are reported in Van Hofstraeten and Verhetsel (2004). The algorithm uses a traditional methodology: 26 variables are measured on 608 sectors. The variables describe land use, attractiveness and accessibility. Some of these 19th century area City centre Suburbs Urban fringe Figure 2. The urban division of Antwerp 160 H. Hammadou et al. grouping input variables into factors grouping statistical sectors into clusters = cluster factor Downloaded by [176.9.124.142] at 01:28 19 September 2014 spatial zoning algorithm 1 densely-built, large employment 1 infrastructure 2 residential built-up area 2 densely-built, large employment 3 industry, port 3 industry, port 4 green area 4 agriculture 5 parks 5 residential built-up area 6 infrastructure 6 green area 7 parks 8 green residential area 9 open area with scattered housing grouping adjointsectors based on cluster value of sector line infrastructure administrative borders Figure 3. Spatial zoning algorithm: a synthesis. variables are highly correlated; hence, a principal component analysis is applied. It summarizes the 26 variables into six components that are by definition uncorrelated. The number of components is determined by the eigen value ( 1.0); this guarantees that the number of factors is reduced, but still explains a large part of variance (70%). A clustering SZA N 10 km Figure 4. From 608 sectors to 33 destination choice zones in Antwerp by applying a spatial zoning algorithm (SZA) Source: Van Hofstraeten and Verhetsel (2004). Destination Choice Models 161 Downloaded by [176.9.124.142] at 01:28 19 September 2014 method is then applied on the 608 sectors in order to group wards that are similar in terms of the scores on the six components. The 608 wards are grouped into nine clusters of similar land use (Figure 3). The final step consists of defining a reasonable number of destination zones, keeping in mind the observed reality of the study area. The basic underlying assumptions of the applied spatial zoning algorithm (SZA) are: 1. neighbouring statistical sectors with similar land use are grouped together; 2. major linear infrastructures (i.e. river Scheldt, highways and ring roads) serve as major spatial barriers. These physical barriers are the primary borderlines, except at slip roads where developments (i.e. industry) occur at both sides of the highway; 3. other main roads, railways and administrative borders are considered as secondary borderlines; 4. open spaces without major developments are not considered as separate destination zones. They are grouped with other sectors within the corresponding municipality or neighbourhood. In fact the zoning algorithm is a step-by-step process grouping contiguous statistical sectors; it is based on the clustering results, administrative borders and infrastructure elements. By following these steps, we obtain destination zones, which are rather homogenous. We end up with 33 zones (Figure 4). This level of aggregation is not excessive for Antwerp: it better corresponds to the geography of the city (fieldwork), and hence to the understanding of the attraction factors influencing destination choice. The aggregation process is well defined and can be adapted over time or extrapolated to other cities, but as in each aggregation process, strong criticisms can be addressed: heterogeneity exists within each zone, zones can evolve over time, etc. The obtained destination zones will form the input for our choice model that aims at explaining the destination choice and the activity patterns (Section ‘Results’): the dependent variable is the probability of selecting one of these 33 zones as destination (J 33). Travel Data, Activity and Tour Structure The travel data set used is the so-called OVG travel data set collected in 1999 as a result of the Flemish Travel Behaviour Research project. In this survey, each person above the age of five and being a member of the selected sample of households was asked to fill in a travel diary for two consecutive days. This resulted in a large data set, including data on each trip (e.g. activity, mode, distance, and duration) as well as Downloaded by [176.9.124.142] at 01:28 19 September 2014 162 H. Hammadou et al. socio-demographic information on each person and household (e.g. age, income, household type, gender). The original OVG data set of Antwerp contains information on about 30,000 trips made by 5613 different persons (Witlox and Tindemans, 2004; Tindemans et al., 2005; Witlox, 2007). Constructing a destination choice model always starts with the definition of the activity patterns (Kitamura, 2004). There are numerous possible activity and tour structures that a person can build, and there is no unique alternative for the modeller for simplifying and aggregating the various structures to a reasonable (limited) number of choice alternatives. In our modelling approach we only considered the destination of the main stop in each tour, each tour starting and ending ‘at home’. We are aware of the fact that by doing this our approach becomes in fact trip-based. The main stop is here associated to the ‘main activity’; the latter corresponds to the activity that lasts the longest in each tour. This definition is by essence arbitrary and can be criticized. Work is assumed to be a mandatory activity fixed in space. Due to the spatial deterministic character of work trips, only non-work stops are considered in this paper. We are aware that these choices may introduce biases in the estimations. The four possible tour structures are reported in Table 1. The model limits itself to the choice of the main destination of the tour. The alternatives in the destination choice models determine the tour structure and stops for various purposes. Our model estimates the probability that a person, making a stop in a tour, chooses a specific place (zone) as destination. The model includes stops made before and after the main activity in the tour (these stops are called Intermediate). Note that in the end only a relatively small number of trips are used as data input. This data reduction results from the fact that work trips were not analysed, trips with more than three stops were excluded (only a very small percentage), and a certain number of trips had to be excluded because they could not be geocoded due to a lack of spatial information. Table 1. Distribution of tour types in Antwerp Non-work tour type HomeMainHome HomeIntermediateMainHome HomeMainIntermediateHome HomeIntermediateMainIntermediateHome Total Source: OVG Antwerp city region (1999). Frequency % 2711 396 268 122 3497 77.5 11.3 7.7 3.5 100.0 Destination Choice Models 163 Downloaded by [176.9.124.142] at 01:28 19 September 2014 Construction of Geographical Variables Van Wee (2002) stressed the importance of the introduction of spatial variables in the analyses of travel behaviour. Badoe and Miller (2000), Stead (2001) and Handy et al. (2005) also indicated that land use, built environment, density characteristics and accessibility are important types of spatial variables that explain the travel choice behaviour. Hence, several spatial variables were collected for each of the 608 statistical wards, bearing in mind that an individual can not only be influenced by the attractiveness of one particular ward, but also by its surrounding wards. Spatial variables are incorporated into our choice model in two ways: the studied city region is redefined by a limited set of homogeneous destination zones (Section ‘Studied Area and Defining Destination Zones’) and the spatial characteristics of destination zones are introduced in the model as explanatory variables. Three types of geographical variables were constructed: land use (Section ‘Land use variables’), attractiveness (density) (Section ‘Attractiveness variables’), and accessibility (Section ‘Accessibility variables’). Land use variables. Land use variables are created drawing from two databases. In 1996, OC-GIS Flanders developed a first digital land use map for the Flemish. The data set is based on satellite images, soil information and road network information. By using an automatic classification procedure, satellite information is converted into 19 different categories of land use (OC-GIS Vlaanderen, 2002). A second land use data set is MultiNet (2001) collected by TeleAtlas. This data set contains information on administrative borders, road network and specific land use characteristics such as ‘built-up area’. Unfortunately, most details about land use pertain to non-built-up surfaces: hence little is known within urban areas. The surface occupied by each type of land use is expressed in square metres as well as in percentage of the total surface, and is computed for each of the 608 statistical wards. The most interesting variables for Antwerp are: (i) housing development (density, built-up, green residential); (ii) industrial, commercial and port development; (iii) green areas and open spaces; and (iv) infrastructure (highways, district roads, airports, ports). Attractiveness variables. A second group of spatial variables relates to ‘size variables’, giving an indication of the importance of a place of destination in terms of population, employment, shopping opportunities or presence of schools. The expected effect on travel behaviour is obvious: the higher the density, the more destinations within the activity range, and hence, the more trips and multipurpose trips (Van Wee, 2002; Van Acker et al., 2007). Downloaded by [176.9.124.142] at 01:28 19 September 2014 164 H. Hammadou et al. Cervero (1996), Cervero and Knockelman (1997) and Badoe and Miller (2000) showed that, based on the relationship between population density and travel behaviour, a larger concentration of population leads to shorter trip distances and the discouragement of the use and possession of cars. That is why it is interesting to attach the number of inhabitants to each origin and each destination sector. The data used are those provided by the National Institute of Statistics (NIS, 2001). The relationship between employment, travel behaviour and activity patterns is well known. In this respect, Badoe and Miller (2000), p. 251) demonstrated that a higher concentration of employment has a significant impact on travel behaviour. The data used here are the number of jobs provided by the Regional Development Agency of 2001. This is only a rough (but workable) estimation of the exact employment figures of the National Census of 2001, but as we estimate non-work trips, these data are well enough. A third attractiveness variable is the presence of schools. The data used here were provided by the Department of Education of the Flemish Government, and consisted of a list of addresses of all Flemish schools (primary and secondary schools, colleges, and universities). After geocoding the addresses, it was possible to compute the number of schools in each of the 608 statistical sectors. A high number of schools will no doubt have an impact on the modal choice (i.e. bringing or getting children to or from school) and on the distance of school trips. Unfortunately, the size of each school is unknown. A last variable is shopping. This is a crucial variable since shopping trips are very frequent in our (non-commuting) travel data set. We assume that a large number of shopping alternatives leads to shorter trips and to a lower use of cars. An Internet data source, called SCOOT (www.scoot.be), provided us with the addresses of most shopping alternatives. In total approximately 6000 stores (large and small) in the city region of Antwerp were included. Geocoding these addresses made it possible to assign this information to each of the 608 sectors. For practical reasons, we limited ourselves to the presence/absence of stores; no reference is made to their relative importance (surface, turnover, and employees). Hence, we mainly computed a number of proxies for different variables. Accessibility variables. A third important geographical variable is accessibility. This variable was included by calculating the shortest distance path distance and shortest time path distance for each centroid of the 608 sectors by means of the StreetNet 2001 network and ArcView Network Analyst. The StreetNet road network includes information on traffic regulations, such as closed streets, one-way streets, underpass and overpass, and travel surplus. We did however Downloaded by [176.9.124.142] at 01:28 19 September 2014 Destination Choice Models 165 not account for congestion, waiting time at traffic lights or extra time to take turns, but in order to partly compensate some network segments were assigned slightly lower speed levels than the actual maximum authorized speed. For the car mode a network distance and a deduced travel time were calculated. For other transport modes (foot and bike) network distances are used to estimate travel time and a speed factor of 4 km/h for walking and 15 km/h for biking. Briefly recapitulating, Table 2 summarizes the explanatory variables used in the models. Data are rather complex: different types of variables are combined for different data levels. However, by doing so, spatial planners are able to analyse sensitivities at different levels. The model can also explore socio-economic behaviour and urban development simultaneously. Results In this section our main findings are discussed. First, Section ‘Determining the Functional Form’ reports on the methodological issue of what type of functional form should be used for the utility Table 2. Variables selected for modelling destination choices (definition and types) Data source Levels OVG data Individual Attributes Age Gender Household Income Location Household type Trip GIS Zone Trip Types Continuous Binary (two categories) Discrete (five categories) Discrete (four categories) Discrete (eight categories) Discrete (four categories) Discrete (five categories) Continuous percentage of geographical area by land use type Purpose Transport mode Land use Built-up, housing Industrial/commerce/port area Agriculture and meadowland Housing and other developments Attractiveness variables Continuous frequencies aggregated by zone Inhabitants Shops Schools Jobs Travel time Continuous accessibility measure 166 H. Hammadou et al. Downloaded by [176.9.124.142] at 01:28 19 September 2014 function (linear, BoxCox transformation, or random coefficients). Section ‘Modelling Destination Choices’ discusses the modelling results for all non-work trip purposes, whereas Section ‘Modelling by Purpose: Shopping and Leisure’ is devoted to show the model results for leisure and shopping trips separately. Finally, in Section ‘Aggregated versus Disaggregated Model’ our aggregate findings are compared to the disaggregated approach proposed by Ben-Akiva and Lerman (1985), which consists in composing individual choices from the choice alternative and a sample of the non-selected alternative. All models were estimated using the Biogeme software (Bierlaire, 2007). Determining the Functional Form Prior to analysing the overall modelling results we first concentrate on a particular important methodological issue in discrete choice modelling: i.e. the selection of the type of utility function. Table 3 shows the results. For the sake of clarity, the analysis is limited to one key explanatory variable: travel time. By doing so, we avoid estimation biases and/or changes in the conclusions due to the transformation of the time variable. Time is indeed one of the most important elements in the explanation process. Other tests were also performed (not reported here) with other variables taken individually or together: they all confirmed the results proposed here. Table 3 compares the Table 3. Estimation of the destination choice model: results for different utility functions for the variable travel time Linear utility Accessibility variables Time Mean Variance Lambda (l) Number of estimated parameters Sample size Null log-likelihood Final log-likelihood Likelihood ratio test Rho-square BoxCox transformation Value t-Test Value t-Test 0.55 74.03 1.84 20.42 0.28 Random coefficient Value t-Test 0.93 44.38 0.70 14.70 9.10 1 2 2 3497 12,227 7373 9708 0.397 3497 12,227 7130 10,195 0.417 3497 12,227 7069 10,316 0.422 Downloaded by [176.9.124.142] at 01:28 19 September 2014 Destination Choice Models 167 results obtained with a linear MNL formulation to that of the Box Cox estimation and of mixed logit with random coefficients. In the BoxCox logit, the exponent of the transformation (l) is equal to 0.28 and is significantly different from zero. This means that the transformation of travel time is not linear. For the model with random coefficients, the estimated variance of the distribution of the coefficient of travel time is significantly different from zero; hence, we accept the hypothesis of a random coefficient of time: the perception of travel time varies randomly from one individual to another. These two alternative solutions to the standard MNL lead to a significant reduction of the absolute value of the log-likelihood (high chi-square values): it drops from 7373 in the standard MNL to 7130 in the BoxCox logit and to 7069 in the random coefficient mixed logit model. As a result the random coefficient formulation is preferred but the utility function is kept linear. Hence, we end up with a nested logit model with random coefficients, often referred to as a mixed nested logit (MXNMNL). Modelling Destination Choices In Table 4 the estimation results for destination choice for all non-work trip purposes are presented for two types of models. As expected, travel time appears to be one of the most important variables in the explanation process (0.64). Hence, destinations located further away from the place of residence or intermediate stop location, have a smaller probability of being selected as destination for an activity. Let us add here that travel time may hide many socioeconomic and demographic disparities in a city like Antwerp. The choice of a destination is additionally and significantly influenced by other spatial and socio-economic variables; the signs of the coefficients meet the expectations. Spatial variables include attractiveness as well as land use information. The influence of the number of shopping and employment alternatives is positive: they increase the attractiveness of a destination, and hence its probability of serving as a destination. Moreover, the higher the percentage of surface affected to housing, parks or green area, the higher the probability of choosing a zone as destination. In contrast, industrial land use has a negative effect on the attractiveness of the destination. Note that ‘agriculture’ also has a positive impact on the probability to choose a zone: open ‘agricultural spaces’ are attractive in terms of recreation and leisure, especially in an urban agglomeration. Most socio-economic variables as well as the characteristics of the tours themselves are less or not important in the explanation of the destination, with the exception of the location (suburbs) and the type Downloaded by [176.9.124.142] at 01:28 19 September 2014 168 H. Hammadou et al. (two children and more) of household. This means that personal characteristics are not very important in the modelling process. In other words, an individual chooses the destination that optimizes his/her utility under the constraint of the characteristics of the destination without reference to its personal characteristics with the exception of the transportation mode and some types of households (Table 4). This is a quite important result in terms of town planning: planning new attractive shopping malls or other shopping/service alternatives will have a drastic effect on transportation fluxes within the city. Let us also mention here the importance of the households’ location in the explanation (suburbs). Note further the weak impact of the socio-economic variables, which can be explained by the gross zone sizes and aggregation over purposes, but also by the fact that socio-economic characteristics are less important in non-work trips than for commuting. In most choice modelling approaches, socio-economic characteristics are introduced with specific effects: they hence obtain for each variable as many estimated coefficients as alternatives. In our case, the high number of spatial alternatives necessitates to constrain the coefficients not to vary from one alternative to the other. Each socio-economic variable has as many coefficients as there are alternatives. It seems to be quite difficult to use this model as a deterministic, predictive tool: one variable can counterbalance effects of other variables. This is especially true for land use variables. In order to solve this problem, elasticities are computed. Table 5 and Appendices A and B present direct and indirect (cross) elasticities for the spatial variables and for the four levels of urbanization. By definition, elasticity measures the relative importance of the response of the choice probability to marginal changes in the explanatory variables. It is computed by the weighted average of the individual elasticities for each spatial variable. If, for instance, the number of shops in the ‘19th century area’ increases by 1%, then the probability of choosing a destination in that zone increases by 0.65% and that of the other destinations decreases by 0.035%. It can be noted that for variables such as ‘percentage of land surface devoted to agriculture’ or ‘percentage of land surface devoted to industry’, the observed hierarchy in the elasticities corresponds to the hierarchy in the level of urbanization of the destination zone: the elasticities are higher in the periphery of Antwerp (suburbs and urban fringe) than in the centre (city centre and 19th century area). As expected, the destination zones close to the city centre have higher direct elasticities for the variable ‘number of shops’. The opposite is observed for indirect elasticities. These results support the relationship between the geographical factors and the destination choice. Destination Choice Models 169 Table 4. Parameter estimates for the multinomial logit and the mixed logit Mixed multinomial logit Downloaded by [176.9.124.142] at 01:28 19 September 2014 Value t-Test Accessibility variables Time: Mean 0.75 34.41 Variance 0.51 12.30 Land use variables Agriculture 0.014 3.63 Industry 0.021 5.81 Housing 0.003 2.30 Parks 0.010* 1.79 Green area 0.103 6.12 Size variables Employment 0.00002 3.12 Number of shops 0.00305 22.02 Socio-demographic variables Age 0.005* 0.83 Income Income B500 euro 0.75* 0.96 Household type Single parent with two or 1.25 2.09 more children 0.88* 1.48 Couple with two or more children Household location Suburb 1.46 4.21 Characteristic of chains Purpose: Service 1.11 2.03 Mode: bike 0.40* 0.80 l1 l2 l3 l4 Number of estimated 18 21 parameters Sample size 3497 3497 Null log-likelihood 12,227 12,227 Final log-likelihood 6554 6498 Likelihood ratio test 11,347 11,458 Rho-square 0.46 0.47 *Not significant at 5% level. Mixed nested logit Value t-Test 0.64 0.38 29.14 11.82 0.011 0.013 0.009 0.013 0.092 3.18 4.59 10.02 3.01 6.81 0.00002 0.00173 3.23 12.37 0.006* 1.30 0.71* 0.99 1.10 2.02 0.90* 1.71 0 Fixed 1.06 0.31* 1.00 0.62 0.82 0.63 2.07 0.70 Fixed 7.50 5.43 3.48 170 H. Hammadou et al. Table 5. Direct and cross elasticity on land use and size variables Urban level City centre Downloaded by [176.9.124.142] at 01:28 19 September 2014 Spatial variables Direct Land use variables Agriculture 0.013 (%) Parks (%) 0.000 Green area 0.130 (%) Housing (%) 0.003 Industry (%) 0.000 Size variables Shopping 1.542 alternatives Jobs 0.279 Cross 19th Century area Direct Cross Suburb Direct Cross Urban fringe Direct Cross 0.001 0.078 0.005 0.247 0.007 0.275 0.005 0.000 0.010 0.016 0.001 0.385 0.020 0.007 0.000 1.145 0.031 0.000 0.000 1.055 0.015 0.000 0.388 0.024 0.325 0.010 0.315 0.006 0.000 0.015 0.001 0.117 0.002 0.127 0.001 0.115 0.646 0.035 0.194 0.010 0.128 0.003 0.021 0.154 0.007 0.100 0.003 0.048 0.001 Modelling by Purpose: Shopping and Leisure In the previous section we considered all non-work trip purposes together. Common practice is however to consider subgroups of trips, for instance by type or purpose; this reduces heterogeneity in the data and hence avoids misspecification of the global estimators and increases the quality of the model. In this section, the behaviour of two subgroups is considered; we test if greater homogeneity enhances the modelling results. Four types of trip purposes were originally considered separately: leisure, shopping, visiting someone and services. Leisure and shopping were however the only one for which there were enough observations for obtaining significant statistical results. The modelling results are reported in Table 6. The results obtained for subgroups are close to those reported in Table 4 (all data): socio-economic characteristics of the individuals have only a very small impact on the destination choice; transportation time and spatial characteristics remain important explanatory factors in destination choice. However, the analyses by subgroups give a better fit, as far as shopping is concerned; the Rho-square increases from 0.47 (i.e. the result taken from Table 4) to 0.53. This is not the case for leisure trips where Rho-square decreases significantly from 0.47 to 0.37. In a way this can be explained by the definition of the activity: ‘leisure’ is vague and refers to sport, cinema, etc. as well as simply Destination Choice Models 171 Table 6. Mixed nested logit for shopping and leisure trips Shopping Downloaded by [176.9.124.142] at 01:28 19 September 2014 Value t-Test Accessibility variables Time: Mean 0.67 20.72 Variance 0.32 7.27 Land use variables Agriculture 0.01 2.93 Industry 0.02 3.60 Housing 0.01 6.50 Parks 0.02 2.67 Green area 0.11 6.01 Size variables Employment 0.00001* 1.14 Number of shopping 0.00183 8.91 Socio-demographic variables Age 0.02 2.86 Income: IncomeB500 euro 1.41* 1.44 Household type Single parental with two or 0.40* 0.52 more children 0.12* 0.17 Couple with two or more children Characteristic of chains Mode: bike 0.11* 0.18 l1 1.00 0.00 l2 0.56 14.28 l3 0.81 21.07 l4 0.92 8.56 Number of estimated parameters 17 Sample size 1881 Null log-likelihood 6577 Final log-likelihood 3068 Likelihood ratio test 7018 Rho-square 0.53 Leisure Value t-Test 0.52 0.33 15.43 6.65 0.01* 0.01* 0.01 0.02 0.05 1.65 1.30 5.95 2.36 2.27 0.00002 0.00177 2.63 7.49 0.01* 1.65* 1.47 0.00 1.88* 1.82 1.61* 1.78 0.04* 1.00 0.63 0.80 0.41 0.05 0.00 10.18 17.48 4.81 17 1090 3811 2397 2828 0.37 *Not significant at 5% level. ‘walk’. Moreover, the location of this kind of activities is also often vague. Even if our data set is quite large, it is not large enough to consider separate modelling of smaller subgroups of leisure activities. Leisure activities tend to occur at random. ‘Shopping’ corresponds to a more homogeneous definition; that is why results are much better in terms of Rho-square. Compared to Table 4, we observe that the number of jobs does not affect the destination choice for shopping 172 H. Hammadou et al. purposes (at the level of analysis, jobs are indeed concentrated in other places than shops), and age enters positively and significantly in the equation. Shopping seems in our case to affect more adults and even elderly people than youngsters. One could also argue here that the choice set for shopping should be different to that of leisure; this is not the case here because of the spatial aggregation adopted. At this level of aggregation most purposes are encountered in each zone. Downloaded by [176.9.124.142] at 01:28 19 September 2014 Aggregated versus Disaggregated Model Throughout this paper we adopted a nested logit structure for handling the IID restrictions. We are aware that this approach can be seen as extremely rigid and afflicted by the arbitrariness of the definition of the spatial aggregates at successive scales as well as by the implicit assumption that all the individuals perceptually delineate the alternatives at various scales in the same fashion. This justifies our rigourous zoning of the city (Section ‘Studied Area and Defining Destination Zones’) and the comparison of several modelling results. In this final section we compare the results obtained on spatially aggregated data to spatially disaggregated choice alternatives with a model formulation suggested by Ben-Akiva and Lerman (1985) for all trip purposes (see also Appendix C). On the average and as expected, the Rho-square is higher in the aggregated process (the well-known phenomenon in spatial statistics). The sign of the coefficients tend to be similar with the exception of that variable ‘suburbs’. It has a positive effect in the disaggregated model and the inverse is observed in the aggregated model. This can easily be explained by the fact that the intra-zone homogeneity is larger in suburban areas after the aggregation process. Last but not least, the values of the coefficients obtained for disaggregated data are difficult to compare to those obtained with spatially aggregated data: scale does not only affect the statistical computation of the coefficients but also generates differences due to the spatial reality. Let us give one example: single parent households with at least two children have a much stronger coefficient in disaggregated models. This is due to the fact that these types of family are concentrated in some small wards characterized by social housing. At this stage, we note that aggregation has advantages but also leads to biases in the models. Advantages are the reduction of the number of alternatives, all destinations are taken into account in the modelling process, the easiness of modelling, the clearness of the interpretation, and the ‘better’ statistical level of explanation (Rho-square). The weaknesses of the aggregated destination choice model mainly depend upon the aggregation rule adopted: the delineation of the new zones can differ with the aggregation rule, and hence influence the modelling Destination Choice Models 173 results. This is a well-known geographical problem linked to the socalled modifiable areal unit problem (MAUP). Moreover, the intrazone homogeneity will highly depend upon the aggregation rule, and it will hence affect the quality of the adjustments. Downloaded by [176.9.124.142] at 01:28 19 September 2014 Conclusions and Future Research This paper has compared several destination choice models for and particularly with the introduction of the characteristics of space. The application was limited to the city region of Antwerp and to one data set (OVG). The results seem to be quite promising, both methodologically and empirically. When considering space in destination modelling, the main methodological problems encountered are: (i) summarizing the spatial reality by a few variables; (ii) defining independent spatial alternatives; (iii) disposing of GIS (adequate data, software and ‘life ware’); and (iv) choosing an adequate formulation for the model choice. This explains why only a few approaches of this problem are to be found in the discrete choice literature. In our case, several variables were created in order to ‘measure’ space and spatial attractiveness. Several modelling methodological formulations were also developed and compared in order to avoid the numerous methodological pitfalls of discrete choice modelling; in our case, the MXNMNL seems to be the best formulation. The application consisted in comparing different formulations of the model and interpreting the parameters for the present situation in Antwerp. We showed how difficult it was to represent space in the analysis of travel patterns and how little the socio-economic characteristics of the individuals/households explain the observed behaviour compared to spatial characteristics. The choice of model estimation influences the results only to a small extent. We are aware that the set of variables introduced in the models is very limited. At the light of the results presented in this paper, we do think that the major challenges in future understanding destination choice are not methodological but behavioural: developing better measurements of the factors that influence destination choice and developing better understanding of the processes (i.e. dynamics) underlying destination choices. Let us add here that the models used were also tested for simulating planning effects: we analysed the impact of a specific change in the choice alternatives. Two new urban development projects were compared. According to the simulation results, one project is more attractive to inhabitants of the city region than the other. This can be explained by the fact that a project containing new shopping facilities, a municipal park, housing and offices obviously attracts more people than an industrial project containing no residential or shopping Downloaded by [176.9.124.142] at 01:28 19 September 2014 174 H. Hammadou et al. facilities (see for more details Verhetsel et al., 2005). By using this approach, public stakeholders can encourage developments in specific areas and study the impact of their policy measures on the overall mobility. They can also play an active role in investing in land development, housing, infrastructure, etc. Whatever the simulation, the characteristics of space seem to be a decisive variable in destination choice modelling. Further analyses have to be done. Particular attention has to be paid to testing the sensitivity of the model to changes in spatial and behavioural measures. Avenues for future research also consist in adding new variables or new measurement of the urban reality in the explanatory process. 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Appendix A: Direct and cross elasticity of spatial variables on each zone Percentage zonal Percentage zonal of agriculture of housing Urban level City centre 19th Century area Suburbs Zone Direct Indirect Direct Indirect 0.013 0.031 0.064 0.023 0.128 0.116 0.084 0.071 0.188 0.127 0.268 0.301 0.334 0.247 0.294 0.498 0.488 0.312 0.348 0.271 0.286 0.424 0.028 0.042 0.111 0.031 0.357 0.256 0.171 0.187 0.108 0.321 0.458 0.166 0.130 0.222 0.381 0.263 0.550 0.707 0.197 0.496 0.488 0.663 0.004 0.023 0.419 0.012 0.570 0.486 0.832 0.565 0.333 0.573 0.558 0.347 0.232 0.965 0.665 0.922 0.521 0.276 0.583 0.552 0.444 0.270 0.008 0.031 0.724 0.016 1.593 1.069 1.694 1.481 0.191 1.449 0.955 0.191 0.091 0.868 0.861 0.487 0.587 0.625 0.329 1.012 0.756 0.423 Percentage zonal of built-up area Direct 0.482 0.710 0.619 0.245 0.302 0.317 0.492 0.345 0.216 0.367 0.344 0.138 0.028 0.677 0.282 0.429 0.320 0.050 0.000 0.273 0.335 0.196 Percentage zonal of industry Number of shopping Number of employment Indirect Direct Indirect Direct Indirect Direct Indirect 1.015 0.969 1.069 0.340 0.844 0.697 1.001 0.904 0.124 0.926 0.588 0.076 0.011 0.609 0.365 0.226 0.361 0.113 0.000 0.501 0.572 0.307 0.000 0.000 0.000 0.000 0.015 0.016 0.000 0.028 0.921 0.056 0.009 0.367 0.701 0.082 0.011 0.162 0.000 0.001 0.028 0.042 0.044 0.003 0.000 0.000 0.000 0.000 0.041 0.036 0.000 0.072 0.528 0.141 0.015 0.202 0.274 0.074 0.014 0.085 0.000 0.003 0.016 0.077 0.074 0.005 1.333 1.315 0.749 0.149 0.427 0.410 0.646 0.417 0.093 0.584 0.312 0.145 0.099 0.130 0.098 0.294 0.102 0.108 0.014 0.087 0.367 0.455 2.806 1.795 1.294 0.206 1.193 0.903 1.315 1.091 0.054 1.476 0.534 0.080 0.039 0.117 0.127 0.155 0.114 0.246 0.008 0.159 0.626 0.712 0.029 0.035 0.030 0.031 0.005 0.008 0.013 0.005 0.046 0.019 0.022 0.024 0.027 0.005 0.003 0.021 0.001 0.005 0.006 0.006 0.004 0.003 0.061 0.047 0.051 0.042 0.014 0.018 0.027 0.013 0.026 0.048 0.038 0.013 0.011 0.005 0.004 0.011 0.001 0.012 0.003 0.011 0.007 0.005 177 1 2 3 4 5 7 8 11 6 9 10 12 13 14 15 16 19 20 21 22 24 25 Size variable Destination Choice Models Downloaded by [176.9.124.142] at 01:28 19 September 2014 Land use variable Appendix A. (Continued) Downloaded by [176.9.124.142] at 01:28 19 September 2014 Land use variable Percentage zonal Percentage zonal of agriculture of housing Urban level Urban fringe Zone Direct Indirect Direct Indirect 26 27 29 30 33 17 18 23 28 31 32 0.251 0.825 1.055 0.431 0.191 0.257 0.706 0.190 0.985 0.448 0.193 0.777 0.233 0.211 0.068 0.369 0.581 0.130 0.503 0.330 0.002 0.537 0.359 0.650 0.833 0.279 0.448 0.397 0.888 0.358 0.787 0.061 0.422 1.114 0.184 0.167 0.044 0.866 0.899 0.164 0.948 0.263 0.000 1.174 Size variable Percentage zonal of built-up area Direct 0.206 0.453 0.255 0.008 0.215 0.137 0.143 0.132 0.453 0.000 0.288 Percentage zonal of industry Number of shopping Number of employment Indirect Direct Indirect Direct Indirect Direct Indirect 0.639 0.128 0.051 0.001 0.417 0.309 0.026 0.348 0.152 0.000 0.801 0.000 0.006 0.000 0.214 0.013 0.005 0.031 0.014 0.000 1.192 0.035 0.000 0.002 0.000 0.034 0.025 0.012 0.006 0.038 0.000 0.005 0.096 0.249 0.674 0.104 0.041 0.096 0.200 0.135 0.195 0.240 0.000 0.033 0.771 0.190 0.021 0.006 0.185 0.452 0.025 0.517 0.080 0.000 0.092 0.003 0.007 0.001 0.154 0.002 0.015 0.003 0.001 0.005 0.015 0.003 0.008 0.002 0.000 0.024 0.004 0.033 0.001 0.003 0.002 0.000 0.009 178 H. Hammadou et al. Table (Continued) Urban level City centre SHOPPING Land use variables Percentage zonal of agriculture Percentage zonal of green area Percentage zonal of housing Percentage zonal of industry Percentage zonal of parks Size variables Number of shopping alternatives LEISURE Land use variables Percentage zonal of green area Percentage zonal of parks Percentage zonal of housing Size variables Number of shopping alternatives Number of jobs 19th Century area Suburbs Urban fringe Direct Indirect Direct Indirect Direct Indirect Direct Indirect 0.013 0.159 0.003 0.000 0.000 0.001 0.012 0.000 0.000 0.000 0.078 0.474 0.359 0.018 0.021 0.005 0.024 0.023 0.001 0.001 0.247 1.409 0.301 0.140 0.009 0.006 0.039 0.009 0.002 0.000 0.275 1.299 0.292 0.152 0.000 0.005 0.018 0.006 0.001 0.000 1.603 0.121 0.671 0.038 0.202 0.010 0.134 0.003 0.073 0.000 0.003 0.006 0.000 0.000 0.218 0.031 0.367 0.011 0.001 0.023 0.648 0.015 0.308 0.018 0.000 0.009 0.598 0.000 0.298 0.008 0.000 0.006 1.577 0.278 0.119 0.021 0.660 0.154 0.037 0.007 0.199 0.100 0.010 0.003 0.131 0.049 0.003 0.001 Destination Choice Models Downloaded by [176.9.124.142] at 01:28 19 September 2014 Appendix B: Directs and cross elasticity of spatial variables on each urban level for leisure and shopping 179 Downloaded by [176.9.124.142] at 01:28 19 September 2014 Multinomial logit Ben-Akiva type Value Accessibility variables Time Land use variables Agriculture Industry Housing Parks Green area Size variables Employment Number of shopping Socio-demographic variables Age Income Income B500 euro Household type Single parent with two or more children Couple with two or more children Household location Suburb Characteristic of chains Purpose Service Mode Bike 0.56 0.013 0.001 0.000 0.001 0.012 0.00015 0.01303 t-Test 66.45 6.62 0.35* 0.27* 0.28* 3.74 7.07 26.40 Multinomial logit zonal approach Value t-Test 0.43 45.52 0.02 0.02 0.01 0.03 0.09 6.62 4.93 12.12 5.45 5.75 0.00002 0.00256 3.60 18.02 0.03 1.30* 0.01 1.43* 3.10 0.08* 0.73 1.06* 20.13 29.59 6.62 0.00* 1.00 1.01 1.76* 1.76* 20.56 34.65 1.45 4.56 1.65 0.05* 1.02 2.00 6.04 0.04* 0.37 0.86* 180 H. Hammadou et al. Appendix C: Aggregated versus disaggregated multinomial logit Appendix C. (Continued) Multinomial logit Ben-Akiva type Value Number of estimated parameters Sample size Null log-likelihood Final log-likelihood Likelihood ratio test Rho-square *Not significant at 0.001 level. t-Test 15 3489 10,612 6220 8784 0.41 Multinomial logit zonal approach Value t-Test 15 3497 12,227 6743 10,968 0.45 Destination Choice Models Downloaded by [176.9.124.142] at 01:28 19 September 2014 Table (Continued) 181