Joint models for analysis of household trip frequency and vehicle ownership in Chennai city

This study investigates some of the key determinants of vehicle ownership (number of two-wheelers and cars) and the trip frequency at the household level using data from Chennai city, India. Potential endogeneity between the number of vehicles present in a household and trip frequency is tested systematically. Vehicle ownership is represented in two ways: (1) The total number of vehicles in a household and (2) The number of cars and number of two-wheelers present in the household. The latter approach is more suitable for the Indian context, in view of its more disaggregate nature and the fact that the effects of some explanatory factors differ considerably for the two types of vehicles. Furthermore, the disaggregate representation enables testing for potential endogeneity between number of vehicles present in the two categories. The empirical results indicate that the relationship between vehicle ownership and trip frequency is indeed endogenous. Disregarding this endogeneity can lead to spurious significance of some factors and failure to detect significance of other important factors. Two-wheeler and car-ownership decisions also appear to be correlated at the unobserved level. Some interesting implications of the models and empirical results for demand modeling and management policies are also discussed.