Identifying driver heterogeneity in car-following based on a random coefficient model

As computing capabilities have advanced, random coefficient models have emerged as the mainstream method of dealing with traveler behaviors in transport studies. Car-following models with random coefficients, however, are rarely used, although many kinds of car-following models have been attempted. For the present study, we proposed a rigorous methodology to calibrate a GM-type car-following model with random coefficients, which could account for the heterogeneity across drivers who respond differently to stimuli. To avert both the curse of dimensionality and the lack of empirical identification, which can be a part of dealing with a simulated likelihood, a robust algorithm called the expectation-maximization (EM) was adopted. The calibration results confirmed that random coefficients of the model fluctuated considerably across drivers, and were correlated with each other. The exclusion of these facts might be a potential reason for the difficulty in simulating real traffic situations based on a single car-following model with constant coefficients.