In recent decades, the highway safety research community, including the U.S. Department of Transportation (USDOT), the Federal Highway Administration (FHWA), the Turner Fairbank Highway Research Center (TFHRC), and state Departments of Transportation have supported and conducted extensive full-scale passenger car-barrier crash tests to better understand crash performance of guardrails and barriers and to improve their design and to reduce the likelihood of vehicle-infrastructure crash fatalities and injuries.
Improved understanding of truck-infrastructure crashes will enable the highway community to improve barrier designs, to further reduce the likelihood of vehicle-infrastructure fatalities and injuries, and to reduce highway congestion resulting from severe accidents. In collaboration with the TFHRC, the National Transportation Research Center, Inc., University Transportation Center (NTRCI) has taken an active role in enhancing industry understanding of truck-infrastructure crash behavior through funding the development and enhancement of advanced finite element (FE) computer simulation models of truck-infrastructure crashes. NTRCI is helping provide highway engineers with data to make better, more well-informed roadside infrastructure decisions that enhance the safety of the traveling public.
NTRCI has funded the research team of Battelle, Oak Ridge National Laboratory (ORNL), and the University of Tennessee at Knoxville (UTK) to conduct a three-phase investigation to enhance and refine a FE model for simulating tractor-semitrailer crash events involving barriers and roadside safety hardware such as bridge rails and median barriers. The tractor model was originally developed by the National Crash Analysis Center (NCAC) of George Washington University (GWU) and requires refinement and testing before it can be used by the engineering community for infrastructure design.
In general terms, the plan for conducting this effort over three phases was:
- Phase A: Conduct an in-depth evaluation of the NCAC tractor only FE model, implement selected modifications, and develop a new trailer model.
- Phase B: Complete preliminary modification of combined tractor-semitrailer FE models, provide them to the FHWA Center of Excellence (COE) community for beta testing, and validate them against suitable full-scale crash tests.
- Phase C: Refine the combined tractor-semitrailer FE models and develop an interactive, online FE model user's website and a User's Manual document to facilitate the use of the model.
Phase A was completed in Year 1 of the project and was documented in the Phase A Final Report. Phase B was completed in Year 2 of the project and was documented in the Phase B Final Report. Phase C was completed in Year 3 of the project and the results of that effort are documented the Phase C Final Report.
The intended application of the tractor-semitrailer model is to evaluate the crash performance of roadside safety features based on the crash test guidelines of National Cooperative Highway Research Program (NCHRP) Report 350 Recommended Procedures for the Safety Performance Evaluation of Highway Appurtenances for Test Level 5. In such applications, the tractor serves as a "bullet" vehicle, so model performance is judged by accuracy of load transfer of the vehicle to the barrier and accuracy in simulating the kinematic behavior of the tractor during and after impact.
Current Status of Model
The overall development of the FE model of a sleeper-cab tractor with a 48-foot semitrailer was completed in Phase B. That model was reasonably validated based on comparison with full-scale crash tests results. The general response of that FE model replicated the basic timing and magnitudes of phenomenological events that occurred in full-scale tests of tractor-semitrailer impacts with rigid longitudinal barriers. In Phase C, more representative tractor FE models were created for comparison to the MwRSF test TL5CMB-2 and the TTI test 7069-13 which reflected more closely the geometry of the crash test vehicles. Test TL5CMB-2 used a day-cab tractor with a 129-inch wheelbase and a 48-foot semitrailer and the TTI test 7069-13 used a day-cab tractor with a 144-inch wheelbase and a 45-foot semitrailer.
The impact conditions for test TL5CMB-2 were consistent with the test requirements of National Cooperative Highway Research Program (NCHRP) Report 350 Test 5-12 (e.g., impact speed and angle of 80 km/hr and 15 degrees, respectively). Based on comparison of FEA results, the research team believes that this tractor-semitrailer FE model is reasonably valid for this type of crash simulation, and that it will provide useful results in general barrier design evaluation work regarding impact loads and general vehicle-barrier interaction.
The impact conditions for test 7069-13 were consistent with the test requirements of the 1989 Guide Specifications for Bridge Railings (impact speed of 50 mph and angle of 15 degrees). The research team believes that this tractor-semitrailer FE model can be validated for this type of crash simulation with some minor additional work. Upon final validation, it will provide useful results in general barrier design evaluation work regarding impact loads and general vehicle-barrier interaction.