Browsing by Author "Johnson, Nicholas S."
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- Assessment of Crash Energy - Based Side Impact Reconstruction AccuracyJohnson, Nicholas S. (Virginia Tech, 2011-05-03)One of the most important data elements recorded in the National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) is the vehicle change in velocity, or ?V. ?V is the vector change in velocity experienced by a vehicle during a collision, and is widely used as a measure of collision severity in crash safety research. The ?V information in NASS/CDS is used by the U.S. National Highway Traffic Safety Administration (NHTSA) to determine research needs, regulatory priorities, design crash test procedures (e.g., test speed), and to determine countermeasure effectiveness. The WinSMASH crash reconstruction code is used to compute the ?V estimates in the NASS/CDS. However, the reconstruction accuracy of the current WinSMASH version has not previously been examined for side impacts. Given the importance of side impact crash modes and the widespread use of NASS/CDS data, an assessment of the program's reconstruction accuracy is warranted. The goal of this thesis is to quantify the accuracy of WinSMASH ?V estimations for side impact crashes, and to suggest possible means of improving side impact reconstruction accuracy. Crash tests provide a wealth of controlled crash response data against which to evaluate WinSMASH. Knowing the accuracy of WinSMASH in reconstructing crash tests, we can infer WinSMASH accuracy in reconstructing real-world side crashes. In this study, WinSMASH was compared to 70 NHTSA Moving Deformable Barrier (MDB) - to - vehicle side crash tests. Tested vehicles were primarily cars (as opposed to Light Trucks and Vans, or LTVs) from model years 1997 - 2001. For each test, the actual ?V was determined from test instrumentation and this ?V was compared to the WinSMASH-reconstructed ?V of the same test. WinSMASH was found to systemically over-predict struck vehicle resultant ?V by 12% at time of vehicle separation, and by 22% at time of maximum crush. A similar pattern was observed for the MDB ?V; WinSMASH over-predicted resultant MDB ?V by 6.6% at separation, and by 23% at maximum crush. Error in user-estimated reconstruction parameters, namely Principal Direction Of Force (PDOF) error and damage offset, was controlled for in this analysis. Analysis of the results indicates that this over-prediction of ?V is caused by over-estimation of the energy absorbed by struck vehicle damage. In turn, this ultimately stems from the vehicle stiffness parameters used by WinSMASH for this purpose. When WinSMASH was forced to use the correct amount of absorbed energy to reconstruct the crash tests, systemic over-prediction of ?V disappeared. WinSMASH accuracy when reconstructing side crash tests may be improved in two ways. First, providing WinSMASH with side stiffness parameters that are correlated to the correct amount of absorbed energy will correct the systemic over-prediction of absorbed energy when reconstructing NHTSA side crash tests. Second, providing some treatment of restitution in the reconstruction process will correct the under-prediction of ?V due to WinSMASH's assumption of zero restitution. At present, this under-prediction partially masks the over-prediction of ?V caused by over-prediction of absorbed energy. If the over-prediction of absorbed energy is corrected, proper treatment of restitution will correct much of the remaining error observed in WinSMASH reconstructions of NHTSA side crash tests.
- Development of the WinSMASH 2010 Crash Reconstruction CodeGabler, Hampton Clay; Hampton, Carolyn; Johnson, Nicholas S. (U.S. Department of Transportation, National Highway Traffic Safety Administration (NHTSA), 2012-07)This report describes the development of WinSMASH2010, an extensive update and enhancement to the WinSMASH crash reconstruction code. The specific objectives were (1) to correct known programming bugs in the original WinSMASH, (2) convert the code from the obsolete Delphi language to C-Sharp to allow future upgrades, and (3) to enhance WinSMASH accuracy by implementing an automated method of selecting vehicle specific stiffness coefficients.
- Serious and Fatal Injury Risk in Road Departure Crashes with GuardrailJohnson, Nicholas S. (Virginia Tech, 2015-06-25)Guardrails are a key safety feature of modern roadways. Collisions with many roadside hazards, e.g. trees, poles and culverts, can be dangerous and guardrail prevents many crashes with such hazards. However, using guardrail safely and effectively is a challenging problem in itself. This research examined two aspects of the problem: 1) assessment of the injury risks posed by guardrail itself; 2) determination of appropriate guardrail length. When controlling for other factors, light truck / van / sport utility vehicles (LTVs) showed injury odds 3.9 times greater in end terminal crashes compared to guardrail face crashes, while cars showed no significant increase in injury odds. Additionally, the odds of injury in frontal end terminal crashes appeared to be between 3.9 and 5.0 times lower when the terminal design was compliant with the National Cooperative Highway Research Program (NCHRP) 350 crash testing protocol, compared to non-compliant designs. Rollover occurred in 10 % of all frontal guardrail crashes, and was initiated by the guardrail in roughly 46 % of instances. The evidence indicates that end terminal contact increases rollover odds by 6.9 times compared to guardrail face contact for LTVs, but not for cars. NCHRP 350 compliance of end terminals was not observed to have any significant effect on rollover propensity. In side-impact crashes with guardrail, end terminal crashes represented only about 25% of crashes but accounted for more than 70 % of the injuries sustained. End terminals compliant with NCHRP-350 may be about five times as safe as non-compliant designs, but the difference appears to be overshadowed by the high degree of risk involved in striking any narrow fixed object with the side of the vehicle. A somewhat larger sample appears necessary to make this finding significant at the 95 % confidence level. Only about 20 % of rollovers in non-tracking guardrail side crashes are initiated by contact with the rail; 80 % are initiated by some subsequent contact. Those rollovers which are rail-initiated appear to be about twice as likely to be initiated by a terminal as by the guardrail face. Cars showed odds of minor to severe injury 3.6 times greater than LTVs in end terminal crashes. End terminal designs compliant with NCHRP 350 were not observed to carry significantly different odds of minor to severe injury than non-compliant end terminals. The findings control for driver seat belt use, rollover occurrence, terminal orientation (leading/trailing), control-loss and the number of impact events. Rollover and non-use of seatbelts were observed to carry much larger increases in risk than end terminal type. For cars, electronic stability control (ESC) reduces odds of fatal crashes with roadside barriers by about 50 % For LTVs, ESC reduces barrier fatality odds by about 40 %. Based on the effectiveness levels observed in this research, it is estimated that ESC could prevent about 410 out of 1180 possible barrier-related fatalities per year by 2028, when 75 % of the fleet is estimated to be equipped with ESC. The study findings suggest that ESC significantly reduces road departures into roadside barriers, and/or that ESC changes departure conditions so that barrier crashes have less severe outcomes. This research has compared the current standard procedure for computing guardrail length of need (LON) with 'departure corridors' based on real-world road departure trajectories. Due to the current procedure's simplified treatment of road departure geometry, LON recommended by the current procedure becomes very conservative for hazards located closer to the roadside, and less conservative for hazards located further away. By contrast, the departure corridor technique developed in this research provides a known, precisely defined level of protection which remains the same for different hazard offsets. Departure corridors can be made for any desired level of protection, and the technique provides flexibility in how protection may be defined. Most importantly, the departure corridor technique is fundamentally more realistic than the current standard procedure and gives LON recommendations which provide protection levels that can be easily communicated to policy makers and other stakeholders.