Abstract: This research develops a simple model for car-following with lane-changing that matches field data with considerable accuracy. Current models of this type usually have a large number of parameters. Many of these parameters are unobservable and/or have no physical explanation. The model presented here, on the other hand, is based only on physical principles and requires few parameters. It uses very simple microscopic rules to reproduce the aggregate characteristics of traffic. The movement of any vehicle is only constrained by its mechanical properties, driver comfort, and safety. The model is proved to be fail-safe, e.g., it has no crashes independently of the deceleration bounds. The final product is used in micro-simulations to study the impact that HOV lanes have on traffic. The objective is to suggest simple strategies for increasing the efficiency of HOV lanes and for reducing the disruptions they cause on the general purpose lanes.