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42 notable that 5.3% of all accidents involving SUVs resulted in acteristics. In the context of developing guidelines for curbs rollover. and curbbarrier combinations, it is important to remember The large percentage of SUVs and pickup trucks on that the pickup truck is not only an important test vehicle in today's highways along with their high rollover rate make its own right but also a surrogate for the broader class of nontracking impact with curbs a much more important factor ISTEA vehicles. now than in former years. There has been a great deal of The performance of a curbguardrail combination can be advancement in computation power and in code develop- evaluated using test conditions specified in NCHRP Report ment over the past few years that has enabled computer sim- 350 for evaluating the crashworthiness of the length of need ulation programs to become a very efficient means of analy- section of a longitudinal barrier. There are currently two tests sis. Although nontracking simulations were not included in required to evaluate guardrail systems for TL-3: this project, in theory both tracking and nontracking impacts with curbs could be investigated using a vehicle dynamics 1. Test 3-11, in which a 2000P pickup truck (e.g., Chevro- code, such as VDANL. let 2500) impacts the guardrail at a speed of 100 km/h and impact angle of 25 degrees, and 2. Test 3-10, in which an 820C (e.g., Honda Civic or Ford FULL-SCALE CRASH TESTING Festiva) impacts the guardrail at a speed of 100 km/h and impact angle of 20 degrees. Introduction Full-scale crash testing is the method used by the FHWA to A guardrail system that meets all the strength and safety certify that a barrier system is crashworthy for use on federally requirements specified in NCHRP Report 350 is considered funded highways. Although advancements in computer sim- acceptable for use on all federal-aid roadways within the ulation programs have made it possible to accurately repro- United States. duce and predict complex impact events, full-scale testing is The literature review identified a limited number of full- still essential in evaluating the safety performance of roadside scale tests involving vehicle impacts with curbs and curb appurtenances, including curbs and curbbarrier systems. guardrail combinations. While full-scale crash testing was To evaluate the performance of roadside safety barriers, used in almost every study that involved vehicle-curb impact, impact conditions must meet the standard testing procedures all the tests that involved simple vehicle-to-curb impacts accepted by the FHWA. The current procedures are published were performed using a large 2040-kg passenger sedan. The in NCHRP Report 350. Prior to Report 350, the 2040-kg pas- results of those earlier tests may have little significance senger sedan served as the crash test vehicle representing the regarding the effects of curb impact with the current fleet of large end of the passenger vehicle fleet. Because the large vehicles, which ranges from very lightweight compact cars passenger sedan had virtually disappeared from the vehicle to large, unstable pickup trucks and SUVs. population by the late 1980s and new vehicle types, such as In this project, a full-scale testing program was used to ver- minivans, SUVs, and pickup trucks, had emerged in its place, ify and confirm hypotheses developed from the computer sim- Report 350 replaced the large car with a 2000-kg pickup ulations and to validate and strengthen the conclusions of the truck. The pickup truck introduced new challenges in crash parametric studies. The few full-scale tests of curbbarrier testing due to its high center of gravity, which makes it much combinations that were identified in the literature aided in the more unstable during impacts than the large car. validation of the models so that the number of additional tests The 2000-kg pickup truck was chosen as a replacement for could be minimized. the 2040-kg passenger sedan for several reasons. First, both vehicles had similar mass and were therefore thought to rep- Low-Speed Curb Traversal Tests resent a similar barrier loading. Second, the pickup truck was chosen as a surrogate for a much broader class of vehicles. Full-scale live-drive tests were performed on three dif- The Intermodal Surface Transportation Efficiency Act of 1991 ferent types of curbs (AASHTO B curb, G curb, and verti- (ISTEA) required the FHWA to address the issue of the cal 6-in. curb) at varying speeds and angles (10, 15, 25, and crashworthiness of the emerging SUV fleet; the FHWA 90 degrees). The test area was a gravel parking lot. The curbs responded by adopting the 2000-kg pickup truck in Report were made using reinforced concrete cast in 1.2-m-long sec- 350 as a surrogate for the entire class of SUVs (e.g., pickup tions. Each set of curbs was attached to the ground with steel trucks, SUVs, minivans, and vans), now known as ISTEA rods driven through holes in the curbs into the gravel. The vehicles. While some of the small SUV vehicles have worse area behind the curb was backfilled with gravel up to the top stability characteristics, the pickup truck is one of the least of the curb. The test setup is shown in Figures 26 and 27. stable vehicles in the vehicle fleet. It is characterized by a The vehicle path was marked on the ground using plastic high center of gravity positioned far forward in the vehicle. strips. The driver aligned the vehicle with the strips to attain There is little front overhang and the suspensions are rela- the desired approach angle, accelerated the vehicle to the tively stiff. Testing with the pickup truck has presented some desired speed, and then released the steering wheel just prior difficult challenges because of its inertial and stability char- to striking the curb. After the rear wheels crossed the curb,

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43 Figure 26. Full-scale curb test setup. the driver reasserted control of the vehicle by steering and Moderate-Speed Live-Driver Tracking Tests applying the brakes. Each test was performed multiple times of AASHTO Mountable Curbs to assess the repeatability of the event. The relative displacements of all four wheels and the accel- Full-scale curb traversal tests were next performed at mod- erations in the longitudinal, lateral, and vertical directions at erate speeds (i.e., approximately 56 km/h) with a live driver. two points on the vehicle were measured during each test. The purpose of the tests was to evaluate the trajectory and Figure 27. Full-scale curb test setup--overhead view.