Development of a Sequential Kinking Terminal for W-Beam Guardrails

A new tangent energy-absorbing W-beam guardrail terminal that meets NCHRP Report 350 criteria has been developed. The terminal, designated the SKT-350, dissipates the energy of an encroaching vehicle by producing a series of plastic hinges in the W-beam as the terminal head is pushed down the guardrail. This energy-absorption concept allows for significantly lower dynamic forces on the encroaching vehicle, reducing the vehicle damage, the weight of the terminal head, the propensity for vehicle yaw and roll after impact, and the chances of buckling in the W-beam section. The energy required to move the head down the rail in this design is optimized for current criteria, but by modifying the bending geometry in the head, the average force to displace the head down the rail can be adjusted from values ranging from 11 to 60 kN (2,500 to 13,500 lb), meaning that the system can be easily modified to meet any future changes in safety performance standards. In addition to these important safety advantages, the terminal incorporates a unique cable anchor bracket that closely resembles a breakaway cable terminal anchor and a novel foundation tube design that facilitates the removal of broken posts during repair. Combining the features of reduced forces and head weight, a simple cable box, and more economical soil tubes allows the system to offer the advantages of both reduced cost and improved performance.