The physical meaning is clear and definite when integral calculus method is adopted to establish the basic equations of traffic flow. According to the fluid mechanics, Euler's method, and the concepts of traffic flow system and control field are proposed. The traffic flow system is a vehicles' gather. The control field is a certain district in the lanes. The integral calculus formula is deduced, in which the first derivative of physical measures of system with respect to time equals the partial derivative of physical measures of control field to time plus clear flux of physical measures passin...
