What is Impact Severity?
Impact Severity is an index that assesses the severity of an impact against the tested restraint system based on the results of different parameters. The impact severity is divided in 3 levels, from A to C, according to the growing severity of the consequences of the impact on the car's occupant. The Impact Severity A affords a greater level of safety for the car's occupants than level B and the same for level B compared to level C.
The Impact Severity is calculated by assessing two components: the Acceleration Severity Index and the Theoretical Head Impact Velocity
Acceleration Severity Index (ASI) is probably the main parameter for the calculation of the Impact Severity and is calculated by placing an accelerometer in the centre of the mass of the car and recording the impact against the road restraint system. The ASI is computed all along the impact time and its maximum value is used to evaluate the severity of the impact.
Theoretical Head Impact Velocity (THIV) has been developed for assessing the occupant impact severity for vehicles involved in collisions with road restraint systems. The occupant is considered to be a freely moving object (head) that, as the vehicle changes its speed during contact with the road restraint system, continues moving until it strikes a surface within the interior of the vehicle. The magnitude of the velocity of the theoretical head impact is considered to be a measure of the vehicle to road restraint system impact severity.
The table below show the different levels/classes of impact severity as well as the maximum ASI/THIV permissible values.