Engineers and scientists have tried to understand and measure the forces experienced by an occupant during a collision by using various testing methods under a wide range of impact orientations and severities. Testing impact forces requires a re-creation of collision accelerations, and can be achieved through experimental methods such as sled tests and full vehicle crashes. Within the automotive industry in particular, evaluations of vehicle safety are most commonly determined through the use of crash test dummies in test vehicles. Other testing methods include post-mortem human subject (PMHS) testing, computer simulations, and live human subject crash testing. While each testing method provides valuable information, it is important to recognize the limitations of each method in order to accurately understand the testing results and to be able to apply them appropriately to measure the risk of injury to an occupant in a real-world collision (based on the impact orientation and severity).
Crash test dummies are typically used to measure injury potential in vehicle crash tests by simulating the human response to impacts, accelerations, deflections, forces, and movements generated during a high speed crash. Government-standardized crash tests at or around 60 km/h into a barrier are conducted in order to assess the integrity of the vehicle structure and safety restraints (seat belts and airbags), which are the major aspects of a vehicle’s design that determine its “crashworthiness” (i.e. safety for the occupants). Transducers, sensors, and data loggers located within the modern dummy or test vehicle record the forces and accelerations experienced by the vehicle and the occupant. The resulting accelerations from these crash tests typically exceed 25 g, and can be as high as 40 g. Acceleration (which is measured in g) causes forces on a weight. An occupant in this kind of a crash would experience forces equivalent to 25 to 40 times their weight! This data is compared with human physiological measurements primarily derived from testing with PMHS in order to evaluate the accuracy of the crash test dummy. While the use of crash test dummies has shown to be reliable, repeatable, and similar to the response of PMHS seen in standard high speed crashes tests, the lack of neuromuscular activity affects the actual response which occurs in humans in real world vehicle-to-vehicle collisions, especially in moderate or lower speed crashes. However, the forces which would be hypothetically generated during the high speed crash tests on a live human are much greater than the forces produced by the human body in order to resist movement, and therefore a live human’s motions would be similar to that of a PMHS or crash test dummy in higher speed crashes.
The use of live human subjects for the purposes of crash testing is not as common compared to testing using crash test dummies and PMHS due to the risk to the human subject. While live high speed human subject testing is not currently conducted, in the past, researchers such as colonel John Paul Stapp M.D., Ph.D., conducted high speed human subject testing in the late 1940s and 1950s. This research was invaluable for the advancement of occupant biomechanics, as it led to a better understanding of injury mechanisms and resulted in improved seat and vehicle design.
Currently, even moderate speed human subject testing is unacceptable by modern day ethical standards because subjects may experience some symptoms, and researchers are unable to conduct experiments that put their subjects under such risk. However, low speed crash testing using live human subjects has been conducted and is valuable for studying occupant kinematics in low speed collisions. More specifically, crash test dummies and PMHS do not necessarily exhibit a similar response to that of live humans during low speed crashes. This is likely due to the influence of the live human subject’s neuromuscular response (bracing, muscles contracting during and after the collision). Research has shown that bracing during a low speed collision can reduce occupant motion and the therefore may decrease the risk of injury, particularly in the neck. However, given the enforced restrictions in using live human subjects for testing where there is a potential for injury, much of this research is only able to be conducted at low speeds, wherein the vehicle speed changes are typically less than 15 km/h and accelerations are less than 10 g.
In summary, crash test dummies, PMHS, and live human test subjects each have a role to play in determining occupant safety in vehicle performance. Testing with crash test dummies and PMHS is extremely valuable for understanding high speed collisions without putting human life at risk, but is unable to replicate the exact results of human subject testing in low speed collision scenarios. While each method has its limitations, each provides valuable insight into occupant movement and to help ensure occupants are as safe as possible in the cars on the road today.