The metal box spacer on the nontraffic side of the transition is used to match the width of the barrier to the width of the transition. The Standard Plans show how to transition from metal beam guardrail to concrete guardrail or bridge rail, and have a thrie beam element on the nontraffic side of the transition posts. Without washers, bolts will pull through the rail element if a vehicle strikes, releasing the rail from the post, and allowing the rail to remain elevated as the post is pushed over.ĭo not allow holes to be drilled in the rail elements in the field unless shown on the plans. Plastic blocks used with steel posts have tabs that don’t allow the block to rotate and are not nailed.ĭo not allow use of washers on the rail face unless otherwise shown. Toenailing the blocks to wood posts prevents this rotation. When timber shrinks, it introduces enough slack in the mounting bolts to allow the timber blocks to rotate. The block allows the guardrail to rise slightly on initial impact, reducing a vehicle’s potential for rolling. As a result, the guardrail is farther from the post and decreases the possibility of a vehicle snagging on the post. If there is less than 3 feet of clearance, concrete guardrail should be considered.Ī block attached to the post adds space between the rail element and the post. This detail uses a combination of longer, heavier posts and closer post spacing to stiffen the rail gradually to reduce the deflection of an impact. If there is less than 4 feet, but at least 3 feet of clearance from the face of the guardrail to a fixed object, a strengthened rail section as shown in the Standard Plans should be used. Spacing posts 6 feet 3 inches apart provides resistance to guardrail deflection on impact and lessens the tendency of the guardrail to form a pocket during impact. Guardrail is normally anchored with a terminal system, an end anchor, such as a steel foundation tube or a buried post end anchor, or anchored to a structure using a transition detail.Ĭrash testing shows that the specified height of 30 to 32 inches for Midwest Guardrail System (MGS) is the optimal height to prevent errant vehicles from climbing over the guardrail. Guardrail must be anchored at both ends, in the same way a railing of rope would need to be anchored to function properly. Pay special attention to all connection details. The design of guardrail contains many subtle details, the basis for which may not be readily apparent. The district traffic safety device coordinator should be consulted if questions arise or changes are needed. The details center on metal beam guard railing but can be applied to other types of railings and barriers. The following paragraphs discuss some of the details considered during design and construction. Construction personnel involved in the installation of railings, barriers, and other traffic safety systems should be familiar with Traffic Safety Systems Guidance, which is posted at: Railings and barriers are used to reduce the severity of run-off-the-road accidents, to prevent out‑of‑control vehicles from crossing the median, and to slow errant vehicles. Section 83 Railings and Barriers 4-8301 General 4-8303C Pipe Handrailing, Steel Bridge Railing, Cable Railing, Metal Railing (Tubular), and Chain Link Railing.4-8303B Guardrail End Terminals Inspection.
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