Abstract: First,it is considered that different traffic lane with the same direction can be merged into one direction traffic lane from the space-time varieties of traffic stream,so that the road travel time can be calculated as a whole.Then it is considered that the road travel time is a random process which is varied with the time and obeyed the asymptotically normal distribution and is also the virtual observation.By the influence of the power to the observation,some paroxysmal events can be treated as the normal traffic density.Next the sampling function and the probability distribution of this stochastic process are discussed.On the analyses of the relation of basic parameters such as the speed,the density,the traffic flows,the spatial occupancy is more dynamic when the road travel time is calculated.