Douglas J. Gabauer

Comparison of roadside crash injury metrics using event data recorders

The occupant impact velocity (OIV) and acceleration severity index (ASI) are competing measures of crash severity used to assess occupant injury risk in full-scale crash tests involving roadside safety hardware, e.g. guardrail. Delta-V, or the maximum change in vehicle velocity, is the traditional metric of crash severity for real world crashes. This study compares the ability of the OIV, ASI, and delta-V to discriminate between serious and non-serious occupant injury in real world frontal collisions. Vehicle kinematics data from event data recorders (EDRs) were matched with detailed occupant injury information for 180 real world crashes. Cumulative probability of injury risk curves were generated using binary logistic regression for belted and unbelted data subsets. By comparing the available fit statistics and performing a separate ROC curve analysis, the more computationally intensive OIV and ASI were found to offer no significant predictive advantage over the simpler delta-V.

The effects of airbags and seatbelts on occupant injury in longitudinal barrier crashes

INTRODUCTION Longitudinal barriers, such as guardrails, are designed to prevent a vehicle that leaves the roadway from impacting a more dangerous object while minimizing the risk of injury to the vehicle occupants. Current full-scale test procedures for these devices do not consider the effect of occupant restraints such as seatbelts and airbags. The purpose of this study was to determine the extent to which restraints are used or deployed in longitudinal barrier collisions and their subsequent effect on occupant injury. METHODS Binary logistic regression models were generated to predict occupant injury risk using data from the National Automotive Sampling System / Crashworthiness Data System from 1997 through 2007. RESULTS In tow-away longitudinal barrier crashes, airbag deployment rates were 70% for airbag-equipped vehicles. Compared with unbelted occupants without an airbag available, seat belt restrained occupants with an airbag available had a dramatically decreased risk of receiving a serious (MAIS 3+) injury (odds-ratio (OR)=0.03; 95% CI: 0.004-0.24). A similar decrease was observed among those restrained by seat belts, but without an airbag available (OR=0.03; 95% CI: 0.001- 0.79). No significant differences in risk of serious injuries were observed between unbelted occupants with an airbag available compared with unbelted occupants without an airbag available (OR=0.53; 95% CI=0.10-2.68). IMPACT ON INDUSTRY This study refutes the perception in the roadside safety community that airbags rarely deploy in frontal barrier crashes, and suggests that current longitudinal barrier occupant risk criteria may over-estimate injury potential for restrained occupants involved in a longitudinal barrier crash.

METHODOLOGY TO EVALUATE THE FLAIL SPACE MODEL BY USING EVENT DATA RECORDER TECHNOLOGY

The flail space model, which was developed in the 1980s, has become the standard method for estimating occupant risk in full-scale crash tests involving roadside safety features. The widespread availability of air bags and increased seat belt usage rates in todays vehicle fleet, however, raise serious questions concerning the validity of the model. Recent installation of event data recorders (EDRs) in a number of late-model vehicles presents a different perspective on the assessment of the validity of occupant risk based on the flail space model. EDRs are capable of electronically recording data such as vehicle speed, brake status, and throttle position just before and during an accident. Of particular interest is the EDRs ability to document the deceleration of a vehicle during a collision event. A methodology using EDR data to investigate the capability of the flail space model to predict injury to air bag-restrained occupants and results of a preliminary analysis based on implementation of the developed methodology on a limited data set are presented. Most of the analysis is limited to the occupant impact velocity because of insufficient data for evaluation of the occupant ridedown acceleration. The longitudinal occupant impact velocity was found to be a good predictor of overall injury, chest injury, and, to a lesser extent, lower extremity injury. For the head and upper extremity body region, the longitudinal occupant impact velocity is a weak predictor of injury.

Influence of horizontally curved roadway section characteristics on motorcycle-to-barrier crash frequency

The purpose of this study was to investigate motorcycle-to-barrier crash frequency on horizontally curved roadway sections in Washington State using police-reported crash data linked with roadway data and augmented with barrier presence information. Data included 4915 horizontal curved roadway sections with 252 of these sections experiencing 329 motorcycle-to-barrier crashes between 2002 and 2011. Negative binomial regression was used to predict motorcycle-to-barrier crash frequency using horizontal curvature and other roadway characteristics. Based on the model results, the strongest predictor of crash frequency was found to be curve radius. This supports a motorcycle-to-barrier crash countermeasure placement criterion based, at the very least, on horizontal curve radius. With respect to the existing horizontal curve criterion of 820 feet or less, curves meeting this criterion were found to increase motorcycle-to-barrier crash frequency rate by a factor of 10 compared to curves not meeting this criterion. Other statistically significant predictors were curve length, traffic volume and the location of adjacent curves. Assuming curves of identical radius, the model results suggest that longer curves, those with higher traffic volume, and those that have no adjacent curved sections within 300 feet of either curve end would likely be better candidates for a motorcycle-to-barrier crash countermeasure.

Evaluation of Threshold Values of Acceleration Severity Index by Using Event Data Recorder Technology

The acceleration severity index (ASI) is used to evaluate the potential for occupant risk in full-scale crash tests involving roadside safety hardware. Despite the widespread use of the index across Europe, there is a lack of research relating this metric to occupant injury in real-world collisions. Recent installation of event data recorders (EDRs) in a number of late-model vehicles presents a different perspective on the assessment of the validity of occupant risk based on the ASI. EDRs are capable of electronically recording data such as vehicle speed, brake status, and throttle position just before and during an accident. Of particular interest is the EDRs ability to document the deceleration of a vehicle during a collision event. This research used EDR technology to investigate the correlation between the ASI threshold limits and the potential for occupant injury in crash events. The longitudinal ASI was found to be a good predictor of overall injury, and the intent of the current preferred threshol...

Characterization of roadway geometry associated with motorcycle crashes into longitudinal barriers

ABSTRACT Motorcycle impacts into longitudinal traffic barriers such as w-beam guardrails often result in severe or fatal rider injury. Countermeasures exist to mitigate the injury consequences of these crashes, but research suggests that these devices are cost-effective only at locations predisposed to this crash type. Unfortunately, little information is available on specific roadway characteristics of these crashes. The objective of this study was to determine specific roadway characteristics associated with motorcycle-to-barrier crashes in the context of other motorcycle crash types and identify features of locations experiencing multiple barrier crashes. Data included a total of 1,511 police reported motorcycle crashes coupled with detailed roadway data from two U.S. states, Washington and Ohio. Compared to all other single-vehicle motorcycle crashes, motorcycle impacts with barriers were found to be significantly more likely on smaller radius horizontal curves and sections with grade in excess of 3%. With regard to the sole quantitative recommendation of placing countermeasures on horizontal curves with radii fewer than 820 feet, agencies may want to carefully consider whether direct application of this criterion is prudent given the available data.

Real-World Performance of Longitudinal Barriers Struck by Large Trucks

Very little is known about the real-world performance of traffic barriers when subjected to impacts by large trucks. This study investigated real-world impacts of large trucks into traffic barriers to determine barrier crash involvement rates, the impact performance of barriers not specifically designed to redirect large trucks, and the real-world performance of barriers specifically designed for large trucks. Data sources included the Fatality Analysis Reporting System (2000 to 2009), the General Estimates System (2000 to 2009), and the Large Truck Crash Causation Study (155 in-depth crashes of large trucks into barriers). Impacts of large trucks into longitudinal barriers constituted 3% of all police-reported impacts into longitudinal barriers and roughly the same proportion of barrier fatalities. A logistic regression model predicting barrier penetration showed that the risk of a large truck penetrating a barrier increased by a factor of 6 for impacts with barriers designed primarily for passenger vehicles. Although barriers specifically designed for impacts by large trucks performed better than barriers not specifically designed for impacts by heavy vehicles, the penetration rate of the former was 17%. This penetration rate is of concern, because barriers used for higher test levels are designed to protect other road users, not the occupants of large trucks. Barriers not specifically designed for impacts by large trucks prevented penetration by a large truck approximately half the time. This finding suggests that adding costlier barriers that meet higher test levels may not always be warranted, especially on roadways with lower truck volumes.

Secondary collisions revisited: real-world crash data and relationship to crash test criteria

Objectives: Previous research conducted in the late 1980s suggested that vehicle impacts following an initial barrier collision increase severe occupant injury risk. Now over 25 years old, the data are no longer representative of the currently installed barriers or the present US vehicle fleet. The purpose of this study is to provide a present-day assessment of secondary collisions and to determine if current full-scale barrier crash testing criteria provide an indication of secondary collision risk for real-world barrier crashes. Methods: To characterize secondary collisions, 1,363 (596,331 weighted) real-world barrier midsection impacts selected from 13 years (1997–2009) of in-depth crash data available through the National Automotive Sampling System (NASS) / Crashworthiness Data System (CDS) were analyzed. Scene diagram and available scene photographs were used to determine roadside and barrier specific variables unavailable in NASS/CDS. Binary logistic regression models were developed for second event occurrence and resulting driver injury. To investigate current secondary collision crash test criteria, 24 full-scale crash test reports were obtained for common non-proprietary US barriers, and the risk of secondary collisions was determined using recommended evaluation criteria from National Cooperative Highway Research Program (NCHRP) Report 350. Results: Secondary collisions were found to occur in approximately two thirds of crashes where a barrier is the first object struck. Barrier lateral stiffness, post-impact vehicle trajectory, vehicle type, and pre-impact tracking conditions were found to be statistically significant contributors to secondary event occurrence. The presence of a second event was found to increase the likelihood of a serious driver injury by a factor of 7 compared to cases with no second event present. The NCHRP Report 350 exit angle criterion was found to underestimate the risk of secondary collisions in real-world barrier crashes. Conclusions: Consistent with previous research, collisions following a barrier impact are not an infrequent event and substantially increase driver injury risk. The results suggest that using exit-angle based crash test criteria alone to assess secondary collision risk is not sufficient to predict second collision occurrence for real-world barrier crashes.

Limits of Acceptable Rail and Post Deflection in Crash-Damaged Strong-Post W-Beam Guardrail

The guidelines for the testing of strong-post W-beam guardrail, intended to ensure the safety of errant vehicles, are specified in NCHRP Report 350. A limitation of these tests is that they are always performed on new, undamaged guardrail, whereas guardrail along highways is in a continuous cycle of damage and repair. No tests have ever evaluated the performance of deflection-damaged guardrail. A full-scale, two-part crash test was conducted to evaluate the performance of a guardrail with 14.5 in. (368 mm) of prior crash damage. When this guardrail was struck by a 4,409-lb (2000-kg) pickup truck traveling at 62 mph (100 km/h), the vehicle vaulted and came to rest upright behind the barrier. A critical factor was the failure of a post to separate from the rails. Finite element models were used to evaluate the guardrail performance at lower levels of deflection. The crash tests and finite element models demonstrated that rail-and-post deflection of 11 in. (279 mm) or higher resulted in vaulting or rollover. Repair was recommended for strong-post W-beam guardrail with combined rail-and-post deflection exceeding 6 in. (152 mm). This limit allows a margin of safety for variations in soil strength and vehicle height. The existence of rail-only deflection had a minimal effect on the crash performance up to the maximum tested value of 6 in.