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2 Summary of Findings The objectives of this study, âImproving the Compatibility of Vehicles and Roadside Safety Hardware", are to 1) Identify current and future vehicle characteristics that are potentially incompatible with existing roadside safety hardware, 2) assess opportunities for and barriers to improved compatibility, and 3) increase the vehicle and hardware manufacturer's awareness of compatibility problems. Since the early 1990's, the United States vehicle fleet has shown drastic changes in its characteristics. Overall, vehicle size and mass have increased while a large population of drivers have shifted from passenger cars to Sport Utility Vehicles (SUVs) and pickup trucks. The magnitude and implication of these changes as they affect roadside hardware crash outcomes was one area of concentration during this research. Based on early studies, the 820 kg small car and the 2000 kg pickup truck were considered to be representative of the worst cases or extremes of the passenger vehicle population during impacts with roadside devices. Based on vehicle population profiles, this assumption was valid during the early 1980's. However, a steady increase in vehicle size for the compact and small car categories as well as the emergence of SUVs has lead to a significantly different vehicle fleet today. Pickup trucks were found to inadequately represent the crash behavior of SUVs. Also, analysis of fatal crashes involving longitudinal barriers (guardrails and concrete median barriers) indicated that midsize SUVs have nearly 8.6 fatal crashes per million vehicles per year registered during barrier impacts; compared to 4.6 for full size pickup trucks. In addition, it was found that rollover involvement is 10-14% higher for compact and midsize SUVs verses compact and full size pickup trucks. An evaluation of the dynamic characteristics of pickup trucks and SUVs indicated significant differences in the center of gravity location (CG) and vehicle weight distribution. Further, SUVs were found to have a 10% higher rollover risk than pickups of similar wheelbase and track width. A methodology to review real world crash cases from the National Automobile Sampling System/Crashworthiness Data System (NASS/CDS) database was developed to identify patterns and occurrences of incompatibility. In all, 247 crash cases were reviewed thoroughly. These cases involved passenger vehicle impacts with guardrails, concrete median barriers and end terminals. Based on this review, the following observations were made. 1. Under typical impact conditions (i.e. impact angles ⤠25 deg), small and midsize cars involved in guardrail crashes are usually safely redirected with minimal injury to the occupants. This
3 indicates that there are no major compatibility issues between guardrails and these types of vehicles. 2. Impacts with concrete median barriers were found to be more serious. Even at moderate impact angles, significant numbers of car occupants sustained serious injuries. 3. Under normal impact conditions into guardrails and concrete median barriers, significantly higher counts of rollovers were found among SUVs than compact and full-size pickup trucks. 4. A significant number of end terminals intruding into the occupant compartment during side impact collisions with passenger cars were found. 5. Side impact crashes of SUVs involving guardrail end terminals often resulted in severe barrier deformation and a lack of vehicle containment. Often this lack of containment lead to additional harmful impacts with natural features behind the barrier. Passenger vehicle crashes with roadside devices often involve other harmful events or impact characteristics which contribute to the likelihood of serious injury. Data contained in the NASS/CDS system provides good documentation of vehicle behavior and occupant protection; however, several factors that are important for roadside hardware safety analysis are missing. To provide this additional information, supplemental data collection sheets have been created (Section 4.2 Figures 4.2-4.5). These proposed sheets are intended to help accident investigators collect pertinent device and crash characteristics. In addition, supplemental instructions are given to document impacted devices using more detailed scene photographs. In order to identify the vehicle structural characteristics that affected the outcome of roadside hardware crashes, several databases were examined to determine the vehicle dimensions. Upon examination of the structural characteristics of the vehicles contained in the databases, some correlation was found between vehicle global attributes and crash outcomes. Specifically an evaluation of track width and height, overall height, and mass indicated good correlation with crash outcomes and severe injuries. However, more detailed characteristics, such as frame rail spread, frontal overhang and center of force did not show a significant correlation. Further, to identify the most appropriate vehicles for testing roadside hardware devices, vehicle registration data as well as vehicle characteristics were examined. A new vehicle classification method was established using this data. An average vehicle from within each of these classes would be a logical choice as a test vehicle.
4 To solicit ideas from a group of safety experts and to raise awareness to communities who are not exposed to roadside safety issues, a one day workshop was organized. Representatives from the automotive industry, roadside hardware manufacturers and a series of government agencies attended a one day workshop for this purpose. Specific workshop findings include: 1. The automotive industry was not aware of the magnitude and frequency of incompatibilities between roadside hardware and vehicles. Because of this, their current vehicle design strategies do not specifically address these issues. 2. Future roadside hardware testing criteria must take emerging vehicle platforms and design trends into account. The vehicles chosen for testing must be representative of the current vehicle population. 3. Automotive manufacturers are willing to explore the use of finite element methods to evaluate their emerging vehicle designs. Vehicle finite element models can be used to simulate a series of impact conditions with prominent roadside devices. 4. Improved data collection and analysis techniques are necessary to evaluate on-the-road systems and aid in identifying vehicle to roadside hardware incompatibilities.
