A guardrail assembly comprising: a first rail section comprising an upstream end portion, a downstream end portion, a first side and a second side; a second rail section comprising an upstream end portion, a downstream end portion, a first side and a second side, wherein said upstream end portion of said second rail section overlaps with and is secured to said downstream end portion of said first rail section with said first side of the first rail section and said second side of the second rail section facing each other, and wherein said first rail section is moveable relative to said second rail section from a pre-impact position to an impact position in response to an axial impact to the guardrail assembly; a support plate disposed adjacent a second side of said first rail section opposite said first side, and a plurality of fasteners securing said support plate to said first and second rail sections, characterized in that the guardrail assembly further comprises a deforming member secured to said upstream end portion of said second rail section and extending laterally from said second side, wherein said deforming member slideably engages said first side of said first rail section and is adapted to laterally deform said first rail section outwardly away from said second rail section as said deforming member slides along said first side as said first rail section is moved relative to said second rail section from said pre-impact position to said impact position; and wherein said first rail section, when being deformed, biases said support plate laterally such that a tensile force is applied to at least some of the said plurality of fasteners as said first rail section is moved relative to said second rail section from said pre-impact position to said impact position. a first rail section comprising an upstream end portion, a downstream end portion, a first side and a second side; a second rail section comprising an upstream end portion, a downstream end portion, a first side and a second side, wherein said upstream end portion of said second rail section overlaps with and is secured to said downstream end portion of said first rail section with said first side of the first rail section and said second side of the second rail section facing each other, and wherein said first rail section is moveable relative to said second rail section from a pre-impact position to an impact position in response to an axial impact to the guardrail assembly; a support plate disposed adjacent a second side of said first rail section opposite said first side, and a plurality of fasteners securing said support plate to said first and second rail sections, characterized in that the guardrail assembly further comprises a deforming member secured to said upstream end portion of said second rail section and extending laterally from said second side, wherein said deforming member slideably engages said first side of said first rail section and is adapted to laterally deform said first rail section outwardly away from said second rail section as said deforming member slides along said first side as said first rail section is moved relative to said second rail section from said pre-impact position to said impact position; and wherein said first rail section, when being deformed, biases said support plate laterally such that a tensile force is applied to at least some of the said plurality of fasteners as said first rail section is moved relative to said second rail section from said pre-impact position to said impact position.