|TTI Research Supervisor:
Chiara Silvestri, Ph.D.,
Associate Research Scientist
Dusty R. Arrington,
Associate Transportation Researcher
Texas A&M Transportation Institute
College Station, Texas 77843-3135
|Pooled Fund Technical Representative:
Rod Erickson, P.E.
Roadside Safety Engineer
Washington Department of Transportation
P.O. Box 47329
Olympia, WA 98504-7329
Buried (in backslope) terminal designs for beam guardrail were developed under National Cooperative Highway Research Program (NCHRP) Report 350 criteria for 27-inch (27¾-inch) high guardrail systems. Some states have modified this design so that it could be used with 31-inch high guardrail systems. Other agencies are hesitant to use this design for 31-inch high guardrail until it has been crash tested or deemed acceptable for use by Federal Highway Administration (FHWA). The objective of this study was to identify design modifications necessary to adapt a buried terminal design for 27-inch (27¾-inch) guardrail for use with a 31-inch guardrail system and to determine the terminal crashworthiness according to NHCRP Report 350 criteria.
Finite element computer simulation of NHCRP Report 350 test 3-35 according the initial impact conditions of test 404211-13 well replicated the results obtained through full-scale crash testing. Although the model did not return realistic roll rate values, other parameters compare favorably to the test outcomes. In addition, the multi-channel option evaluation through the RSVVP program without inclusion of the roll rate channel suggests that the FE model of the 27¾-inch buried-in-backslope terminal realistically replicate the results observed through the full-scale crash test. Without any additional design modifications, the researchers decided to elevate the rail height of the test article model from the original 27¾ inches to 31 inches and determine the crashworthiness of the new model according to computer simulations.
Results from the computer simulation of test 3-35 against the 31-inch rail high buried-in-backslope indicate that all applicable NHCRP Report 350 evaluation criteria were met. The vehicle was properly contained and redirected and maintained stability throughout the complete impact event. The vehicle interaction with the test article did not suggest any potential for wheel snagging. Review of the plastic strains in both rail and posts suggests that it is unlikely the rail or the posts will fail during the impact event. Occupant risk were also well below NHCRP Report 350 limit values.
Results of the FE simulations for the 27¾-inch and 31-inch rail high buried-in-backslope terminal were compared to determine the 31-inch rail performance with respect to the 27¾-inch rail height. FE computer simulations indicate that the 31-inch rail high buried-in-backslope terminal has a very similar behavior that was observed for the 27¾-inch rail high. In fact, the 31-inch rail height seems to increase the 2000P vehicle stability throughout the entire impact event, maintaining occupant risks well below the limiting values according to the NHCRP Report 350 criteria. Based on this evaluation, the researchers suggest the proposed 31-inch rail high buried-in-backslope terminal design be accepted for FHWA eligibility.