In this article, a new cellular automaton traffic flow model, in which randomisation effect is enhanced with the decrease of time gap and the long time stopped vehicle has large randomisation probability, is presented. Both periodic and open boundary conditions are considered. Under periodic boundary condition, the fundamental diagram and the properties of synchronised flow are studied in detail. Under open boundary condition, different congested patterns induced by an on-ramp are analysed. The results are consistent with the well-known results of Kerner's three-phase traffic theory published before.