Recommended Guidelines for Curb and Curb-Barrier Installations (2005) / Chapter Skim
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Pages 31-45
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From page 31... ...
ANALYSES OF CURB-RELATED SAFETY ISSUES USING CRASH AND INVENTORY DATA Introduction Since the inception of this study, an overall goal has been to use existing databases containing information on crashes, roadway inventory, and traffic to better characterize safety problems associated with curb and curb–barrier combinations on higher-speed roadways. Such information was used directly in the development of the design guidelines since it can provide real-world insight into the magnitude of the problem on various roadway types, the nature of the problem (e.g., how curb impacts are similar or dissimilar to other run-off-road collisions)
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From page 32... ...
Finally, since it is based on fatal crashes, FARS data could not be used to examine differences in injury severities with and without curbs; only the fatal crash failures are present. National Automotive Sampling System -- General Estimates System (NASS-GES)
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From page 33... ...
To help ensure that the curb was directly related to the rollover, all three databases chosen include a "sequence of events" that allowed selection of only rollovers preceded by a curb impact. 1997-99 NASS-CDS 1996-97 Michigan 1996-97 Illinois Crash, Injury, and Rollover Rates per Passing Vehicle for Guardrail Sections with and without Curbs To examine differences in the crash rates and rollover rates for guardrails with and without curbs, Michigan data on guardrail inventory, roadway inventory, traffic and crashes on urban freeway and other urban multilane roads were used in both contingency table analysis and negative binomial models.
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From page 34... ...
FEA was, however, invaluable in the analysis of impacts with curb–barrier combinations. Vehicle dynamics codes only provide information regarding vehicle kinematics and cannot provide information about the vehicle interaction with the barrier.
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From page 35... ...
The primary drawback of finite element simulations is that they must be validated to make sure that the predictions are realistic. There are several public domain vehicle models available from the FHWA/NHTSA National Crash Analysis Center at George Washington University that have been validated for various impact conditions.
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From page 36... ...
The redirection angle of the vehicle in the curb– guardrail simulation exceeded the allowable exit angle specified in NCHRP Report 350. According to criteria M of Report 350, the exit angle from the test article should be less than 60% of the test impact angle, measured at time of vehicle loss of contact with test device.
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From page 37... ...
and G4(2W) finite element simulation (right)
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From page 38... ...
Performing ten finite element simulations with the curb located at different distances from the face of the post, for example, would be straightforward and inexpensive and would allow the analyst to determine the effect of the curb offset on the performance of the barrier. Likewise, curbs with heights varying from 0 to 300 mm could be evaluated easily using finite 38 element simulations.
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From page 39... ...
Initial Contact 0.000 100.8 0.000 100.8 Vehicle starts to yaw 0.056 100.8 0.044 100.6 Wheel impacts post 15 0.104 90.2 0.101 91.3 Wheel impacts post 16 0.193 74.8 0.190 75.7 Rear of vehicle contacts guardrail 0.203 73.2 0.207 73.0 Wheel Detaches 0.215 69.4 0.215 71.3 Vehicle parallel with guardrail 0.283 68.0 0.264 69.0 Vehicle exits guardrail θ = 13.5E 64.0 θ = 14.3E 63.0 TABLE 9 Summary of major impact events of test 471470-26 and G4(2W) finite element simulation (46 )
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From page 40... ...
guardrail was used in the study so that the maximum number of curb types and impact conditions could be investigated.
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From page 41... ...
In 1996, almost 9,500 passenger vehicles (e.g., passenger cars, pickup trucks, vans, and SUVs were involved in fatal rollover crashes. Rollovers accounted for 36% of all fatal crashes involving SUVs and 24.5% of all fatal crashes involving pickup trucks, as illustrated in Figure 25.
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From page 42... ...
While full-scale crash testing was used in almost every study that involved vehicle-curb impact, all the tests that involved simple vehicle-to-curb impacts were performed using a large 2040-kg passenger sedan. The results of those earlier tests may have little significance regarding the effects of curb impact with the current fleet of vehicles, which ranges from very lightweight compact cars to large, unstable pickup trucks and SUVs.
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From page 43... ...
The relative displacements of all four wheels and the accelerations in the longitudinal, lateral, and vertical directions at two points on the vehicle were measured during each test. 43 Moderate-Speed Live-Driver Tracking Tests of AASHTO Mountable Curbs Full-scale curb traversal tests were next performed at moderate speeds (i.e., approximately 56 km/h)
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From page 44... ...
curb-related safety problem; examination of curb-related rollover risk and nature given a crash; comparison of crash, injury, and rollover rates per passing vehicle for guardrail sections with and without curbs; curb-crash severity modeling; and examination of the nature of curb impacts, using crash reconstruction data and comparing extreme and nonextreme crashes. FEA was also used to study the effects of vehicle interaction with curbs and curb–guardrail combinations.
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From page 45... ...
LSDYNA was also used to investigate the effects of installing curbs in conjunction with guardrail, regarding the ability of the barrier to safely contain and redirect an impacting vehicle. 45 Full-scale crash tests were used to validate the computer models.
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