In order to increase roadway capacity retaining safe driving environment IVHS(Intelligent Vehicle Highway Systems) has been introduced claiming that dynamic entrainment of vehicles are feasible with advanced technologies. A longitudinal control scheme was presented requiring dramatic reduction in intervehicular gap in the vicinity of 1 m. Even though safety is guaranteed, accidents might be unavoidable in unexpected situation. In this study, a methodology assessing the severity of critical accident involving several vehicles in the platoon resulting from emergency braking of a preceding vehicle or from sudden deceleration of the failed vehicle is presented. This includes a model specification which is based on the momentum conservation theory, the choice of severity criteria as speed variation from the accident, and sensitivity analysis of the related parameters affecting vehicle performance. The sensitivity measure was demonstrated with respect to various parameters including deceleration rate, response delay, information transfer type within the platoon, mixed vehicle types and arrangement, and collision with restitution. Accident severity was applied to the platoon with 10 vehicles.