Low Speed Rear-End Impact Tests

Experiencing Low Speed Rear-End Impact Tests

Crash test participants "falling out" at 59 Rickenbacker Circle facility. Shown l to r: Tom Braun, Janet Jhoun, Tom Boster, Gary Hesler, Mike Braun. Not shown:

Ted Kobayashi, Brad Wong, Frank Perez.

A 1982 Toyota Celica GT two-door hatchback and a 1984 Ford Mustang were used in seven rear-end impact tests. Two human volunteers were seated in the two front bucket seats within the target vehicle, the 1982 Toyota Celica, and one volunteer operated the bullet vehicle, the 1984 Ford Mustang. The engine of the target vehicle was running with the transmission in neutral. The target vehicle was stationary prior to impact by the bullet vehicle. The subject in the driver's seat of the target vehicle was instructed to apply pressure to the brake pedal as if waiting at a normal stop.

The bullet vehicle had its engine running with the transmission in drive. The volunteer operating the bullet vehicle was instructed to release his foot off the brake, allowing the bullet vehicle at engine idle speed to roll forward over a predetermined distance to the point of impact. This roll distance determined approximate impact speed of the bullet vehicle. All impact tests were aligned bumper-to-bumper rear-end impacts.

Vehicle acceleration data was captured using two triaxial accelerometers. The acceleration time history of the event was used to determine vehicle change in velocity, peak and average accelerations, and duration of impact for each test. Bullet vehicle impact speeds ranged from 3.2 to 10.5 kph (2.0 to 6.5 mph) for the seven impact tests. The change in velocity, or delta-V, for the bullet vehicle ranged from 2.7 to 7.2 kph (1.7 to 4.5 mph). The target vehicle experienced a delta-V range of 2.4 to 7.2 kph (1.5 to 4.5 mph) for the seven impact tests. Coefficient of restitution ranged from about 0.3 to 0.5 for these rear-end impacts, as was determined from the above velocity data. The corresponding impact time durations ranged from 0.09 to 0.124 seconds. Vehicle average and peak acceleration for the seven tests ranged from 0.6 to 2.3g and 0.9 to 4.4g respectively.

General kinematic response and subjective response were documented for the occupants seated in the target vehicle. The volunteers consisted of seven healthy adults (one female and six males) ranging in age from 29 to 61 years and of varying height (5'5" to 6'3") and weight. The volunteers were in normally seated positions wearing three-point lap/shoulder seatbelts and had adequate head support provided by the head restraints. They were instructed to relax prior to impact. As the target vehicle was pushed forward by the impact, both torso and head were accelerated forward with the seat, but the head went at a slower rate. For impacts of sufficient severity, when the head lagged behind the torso, the neck was observed to go into extension. The head restraint was positioned to prevent significant neck extension. In six out of seven of the impact tests, one or both occupants made contact with the head restraint as a result of the impact. The impact test with the lowest delta-V of 2.4 kph (1.5 mph) produced a trivial impact where neither occupant made contact with the head restraint. Test subjects' perception of the forces produced on the head, neck and torso for impact tests resulting in less than a 4.8 kph (3.0 mph) delta-V to the target vehicle were within the range of forces that could be experienced in daily activities. The contact between the head and the head restraint was not a significant blow; it was more of an awareness, as indicated by the volunteers.

Inspections of both the target and bullet vehicles were performed before and after the impact testing. Post-test inspection of the target vehicle did not reveal any damage to the vehicle as a result of this series of tests other than superficial impressions on the plastic cover that were considered cosmetic in nature and barely noticeable. However, when the rear bumper on this vehicle was partially dissembled and examined after the completion of the testing, cracking was noted along the top edge of the foam core. There was no evidence of damage to any of the other bumper components.

In conclusion, the volunteer subjects agreed in their subjective findings that the forces resulting from the impacts that produced a delta-V of 4.8 kph (3.0 mph) or less were comparable to that experienced in daily activities. Moreover, when the severity of impact was delta-V of 4.8 kph (3.0 mph) or less, head contact with the head restraint either did not occur or was so minimal that only a slight awareness was noted. Significant risk of injury appears to be remote for this severity of impact for healthy adults seated normally.