The failure phenomena of a viscoelastic thin film of bitumen and polymer modified bitumen under direct tension tests is investigated in detail, experimentally and theoretically. Using video recording and image processing techniques, the time evolution of failure and film disintegration and separation phenomena were studied. The following failure stages were identified and recorded: Initial (=stage 1), necking (=stage 2), filamentation with void nucleation (=stage 3) and separation (=stage 4). The technique allowed the identification of an additional failure stage for the pure bitumen than the four identified for binders, namely light transparent thinning before void nucleation. The determination of stages to final separation allowed behavioral distinction between the straight run bitumen and the polymer modified bitumen. As the direct tensile tests proceed, in addition to shear forces demonstrative of viscous effects, gravity and capillary forces act on the binder film. In order to understand the relative effect of these forces the order of magnitude of relevant dimensionless numbers, representing ratios of these forces is considered and discussed. The analysis of the above numbers confirms that the flow in bitumen is dominated by viscous effects although capillary forces do play a role at later stages of the experiment with negligible inertia and gravitational effects. The detailed analysis of micromechanical behavior of straight run bitumen and polymer modified bitumen provided further indication corroborating the superior field performance of polymer modified bitumen in porous asphalt. (C) 2012 Elsevier Ltd. All rights reserved.