Accuracy of the Momentum Energy Restitution Method for Offset Inline Minor Rear-End Impacts

In minor inline rear-end accidents, vehicle damage is the primary tangible indicator of impact severity or vehicle change in velocity (ΔV). A technique for calculating change in velocity based on vehicle damage for collinear impacts involves application of the Momentum Energy Restitution (MER) method. Offset inline minor rear-end impact testing, wherein minimal vehicle bumper or contact surface engagement occurs, has not been readily published to date. Thus, instrumented offset inline rear-end impacts were performed utilizing a 1997 Ford F-150 Pickup, 1996 Kia Sephia, and 1995 Chrysler LeBaron GTC to determine if the MER method can accurately calculate a vehicle’s ΔV when collinear contact does not occur. Vehicle engagement involved 5.1 cm to 76.2 cm of overlap with impact speeds ranging between 0.7 m/s and 4 m/s. Test results indicated that a 15.2 cm or less overlap between vehicle impacting surfaces promoted sideswipe impacts or an incomplete transfer of momentum relative to the bullet vehicle’s impact speed. An overlap of greater than 15.2 cm between the vehicle impacting surfaces allowed for complete collisions and transfer of momentum relative to the bullet vehicle’s impact speed. The profile and composition of each vehicle’s impact surface also contributed to complete vs. incomplete collisions. With individual vehicle damage documented before and after each test, application of a modified MER method, which accounts for impacts where measurable crush damage does not occur, was performed based on the measured damage to theoretically calculate each vehicle’s ΔV. The calculated results utilizing the modified MER method were then compared to the test vehicle acceleration traces which were integrated for determination of each test vehicle’s actual ΔV. Comparison of the calculated vs. actual data indicated a high accuracy of prediction (i.e., 1.4 - 33.2% error) for a vehicle ΔV greater than 0.8 m/s via the modified MER method with a vehicle overlap greater than 15.2 cm. When vehicle overlaps were less than 15.2 cm, a sideswipe aspect was introduced and an over calculation (i.e., 202.0 - 844.5 % error) of vehicle ΔV occurred.