Vehicle driven by driver may be considered as control system with driver as a controller and vehicle as controlled system. Changeable vehicle environment is the source of outer forces reaching driver and having effect on vehicle dynamics. Driver efficiency depends on situation on the road, vehicle characteristic and psychical and physical driver features. Driver is included in road-vehicle-driver system as feedback element. His functions can be described as concerning running vehicle input data processing into control of vehicle systems. Parameters describing drives behaviour (eg - driver reaction time delay) can be identified basing on model of system in frequency domain (from transmissibility) or in time domain (from correlation).