The glass transition of linear chain polymers was simulated by means of the bond fluctuation model, employing a Lennard-Jones intermolecular potential and a bond-length intra-molecular potential. The influence of the balance between inter- and intra-molecular potentials on the model prediction was studied and an appropriate range was determined in order to simulate physical ageing. The relationship between molecular mobility and the dynamically accessible volume was shown in comparison with other definitions of specific volume or free volume. The temperature dependence of the dynamically accessible volume shows the vitrification of the material analogously to the temperature dependence of the lattice energy. Dynamically accessible volume has been proposed as a universal parameter to explain glass transition, but in the bond fluctuation model it does not give the same value for all simulated glass transitions. This fact could be corrected by including the Metropolis criterion in the dynamically accessible volume in order to extend the concept to thermal systems. (c) 2005 Elsevier Ltd. All rights reserved.