The car-following model calculates a vehicle's acceleration rate, taking into consideration its relationship with the leading vehicle. In several circumstances, this model is also used as a sub-model for calculating appropriate acceleration rates: (i) preparing to follow another vehicle if two or more lanes merge into a single downstream lane; and (ii) yielding to another vehicle shifting into the same lane. The car-following model used in MITSIM draws upon previous research [Herman et al. (1959), Herman and Rothery (1963), Wicks (1977)]. The model is based on the headway and relative speed of the leading and the following vehicles. Depending on the magnitude of this headway, a vehicle is classified into one of three regimes: free flowing, car following, and emergency decelerating.