In this paper, we investigate the regression vector structure of human skill model. As an example, the human driving skill is described as a hinging hyperplane autoregressive exogenous (HHARX) model, which is able to deal with manipulation modes and their switches simultaneously. Simulation results illustrated that distances from the vehicle to the route side, velocities of vehicle at sampling times vt and vt-i are must be included in the regression vector of HHARX model while modeling human driving skill.