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In this paper, trip frequency is modeled to be the outcome of two underlying latent behavioral mechanisms:(activity) stop-making propensity and trip-chaining propensity. The stop-making propensity is a measure of extent of out-of-home activity participation of an individual. The trip-chaining propensity represents the tendency of a user to combine different activity stops into a series of tours. These propensities are related to the observed activity-based dimensions of tour and stop frequencies. Further, trip frequency is expressed as a linear combination of these two observed activity dimensions. The effect of trip chaining propensity is captured by modeling the excess stop frequency which is defined as the difference between the number of stops and number of tours. A non-zero value of excess stop frequency signifies the occurrence of trip-chaining. However, the stop-making propensity and the trip chaining propensities together determine the number of tours made by an individual, leading to potential endogeneity between tour and excess stop frequency. This framework is operationalized by modeling the two activity dimensions: tour and excess stop frequency as endogenous dimensions using data from Chennai city, India. The associated models are estimated using a three stage least squares (3SLS) technique. The empirical results show that the proposed model which accounts for these mechanisms outperforms conventional trip frequency models. Some explanatory variables influence the two activity dimensions to varying degrees and sometimes in contrasting directions. It is found that individual level models may be more behavioral and …