With considering the influence of relative motion of vehicles in car following behavior, safe driving conditions and lane changing rules, a two-lane cellular automaton traffic model is proposed based on car following behavior, which is able to illustrate the system's metastable state near the critical point and produce simulation results that accord with observed data. With simulation data on lane changing behavior, a study is conducted on relationship between traffic density and number of vehicles meeting lane changing conditions. Lane changing function is defined to describe lane change process under standard driving behavior. Analytical solution of the function is obtained and used to predict traffic density that stabilizes after lane change process, which contributes to further research on vehicle lane changing behavior.