In this study, a bridge rail-to-guardrail transition is analysed to fully evaluate its crashworthiness. A non-linear, large-deformation finite-element simulation programme LS-DYNA is used for the analysis. Previous studies have predicted that the transition was able to successfully contain and redirect a 2000kg pickup truck under National Cooperative Highway Research Program (NCHRP) Report 350 test level 3 conditions. In this study, the transition was subjected to an 8000kg single-unit truck impact according to NCHRP Report 350 test level 4 conditions. Both the model of the 8000kg truck and the transition structure used in this study were acquired from previous successful studies. Results of the simulation study showed that the transition structure was found to be adequate in containing and redirecting an 8000kg truck. It was also determined that the post-impact trajectory of the truck, occupant risk values, article deflections and exit conditions were very similar to those obtained from a similar transition structure previously crash-tested under test level 4 conditions. It was concluded that the finite-element model of the vertical flared-back bridge rail-to-guardrail transition is fairly accurate and can be used in further studies, such as the MASH test level 4 crash simulation with confidence.