Based on more than 180,000 field data coll ected at GuangFuo and JingShi expressway, the relationship between the kinematical characteristics of car following and time headway is analyzed in detail. A new methodology is provided for quantitatively recognizing car-following status on the basis of variational law between the absolute value of relative speed difference and time headway. A coordinated transformation method is devised to identify the turning point from car-following status to free drive status. ...