A W-beam to thrie beam stiffness transition with a 102-mm (4-in.) tall concrete curb was developed to connect 787-mm (31-in.) tall W-beam guardrail, commonly known as the Midwest Guardrail System (MGS), to a previously developed thrie beam approach guardrail transition system. This upstream stiffness transition was configured with standard steel posts that are commonly used by several state departments of transportation. The toe of a 102-mm (4-in.) tall sloped concrete curb was placed flush

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... the backside face of the guardrail and extended the length of the transition region. Three full-scale crash tests were conducted according to the Test Level 3 (TL-3) safety standards provided in AASHTO's Manual for Assessing Safety Hardware (MASH). The first test, MASH Test No. 3-20, was deemed a failure due to guardrail rupture. The stiffness transition was modified to include an additional nested W-beam rail segment upstream from the Wbeam to thrie beam transition element.