فهرست مطالب نویسنده:
s. seyedabrishami
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Scientia Iranica, Volume:28 Issue: 5, Sep-Oct 2021, PP 2471 -2478Destination and departure time choices are interrelated decisions that affect urban travel demand estimation. Most previous studies ignore this interrelation and assume that these decisions are independent. Some other studies use a hierarchy structure, while the literature suggests that destination and departure time are selected simultaneously before the commencing of trips. This paper employs copula-based joint modeling to explore the interdependency between destination and departure time choices. The destination choice modeling is developed using a multinomial logit model, and a binary logit model is used for modeling departure time choice. To obtain a better-fitted model, several copula functions are used thereafter; the frank copula is selected for the final model. Results show that there are some common unobserved factors between these decisions by estimating copula dependence parameters with high statistical significance. Furthermore, there are some commonly observed factors, such as socio-demographic and travel characteristics that appear in the utility functions of both models.Keywords: Joint modeling, Copula, Destination choice, Departure time choice, Logit
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Scientia Iranica, Volume:28 Issue: 4, Jul-Aug 2021, PP 2037 -2052There is a relationship between choosing an activity and duration of that activity, especially for non-mandatory ones. Some previous studies have analyzed the decisions about an activity type and duration independently, though some others have used joint models. This paper contributes to the body of knowledge through using Nested-logit and Copula-based models for assessing the existence of interdependency or a hierarchy between non-mandatory activity choice and the relative duration. In the Nested-logit model, it is assumed that error terms of these decisions are interrelated, though one is influenced by another. In contrast, the Copula-based model can accommodate spatial error correlation across observational units without imposing a restrictive distribution assumption on the dependency structures between the error components. The data from Qazvin, a city in Iran, are used for estimating both Nested-logit and Copula-based models and the best variables explaining both choices for each model have been selected. The final models were compared in terms of log-likelihood at convergence and adjusted likelihood ratio index. The results indicated that there are some common influential observed and unobserved factors between these decisions. Also, Copula-based joint model with ρ_0^2 equals to 0.134 outperforms Nested-logit models and provides a better explanatory power.Keywords: non-mandatory activities, joint model, activity choice, activity duration, Copula, Nested-logit
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