12/9/2023 0 Comments Twitter honolulu trafficA U-channel post of re-rolled rail steel weighing 3 pounds-per-foot or less meets breakaway requirements by itself. A broken or damaged post is easier to remove if it is not driven or set into the ground more than 3.5 feet.īreakaway Devices. Post Support. The post should be driven into the ground and not encased in concrete. It is considered breakaway since it will bend, break or pull out of the ground when it is hit. The U-channel, hot rolled steel post is another common small sign support. Holes are needed for wood posts greater than 4 x 4 inches. A 4 x 4 inch wood post is the largest undrilled wood post recommended to act as a breakaway support. For example, a 6 x 8 inch wood post can be used if the cross section is weakened by drilling two 3-inch holes (drill perpendicular to roadway). Large supports should be drilled to provide the breakaway characteristic. Small wood support is typically a 4 x 4 inch post. One or two posts may be used to make up the sign support, but adding posts too close together can affect crashworthiness. The post may need to be buried even deeper to reduce vandalism and reduce dislodging by heavy winds. This type of post should be buried about 30 to 36 inches deep depending upon the type of soil and backfill check State specifications or with LTAP for embedment depth and backfill material. ![]() Small supports have a cross section of approximately 16 square inches. All posts above 4 x 4 inch nominal size must be drilled perpendicular to traffic flow to allow the post to break away if struck by a motor vehicle. These posts usually come in sizes of 4 x 4 inches to 6 x 8 inches. ![]() Wood posts are frequently used, especially in regions where wood is economical compared to metal type supports. Additional information on acceptable breakaway sign supports can be found at FHWA’s Office of Safety website. All sign supports on highways within the clear zone must either be of a breakaway type meeting the crashworthiness criteria of NCHRP 350 (see references) or be shielded by guardrail, barrier, or an energy absorbing system meeting NCHRP Report 350 or the AASHTO Manual for Assessing Hardware (MASH) criteria. Barriers are typically not installed to shield roadside signs, especially on local roads hence, the design of the post, regardless of the type, must provide the breakaway or yielding feature. A ‘yielding’ support refers to a support that bends, allowing a vehicle to run over it. This includes sign supports that, when struck by a vehicle, separate from the base and are knocked ahead of or up and over the errant vehicle. ![]() ‘Breakaway’ is a term to describe crash tested sign supports that break or bend upon impact. Most posts for roadside post-mounted signs are one of the following types:Ī sign support can become a deadly hazard when struck by a vehicle that drives onto the roadside therefore, there is an MUTCD standard that requires all roadside sign supports in the clear zone (see Appendix B for description of clear zone) to be breakaway, yielding, or shielded by a barrier or crash cushion. Any device that is used to display the traffic sign is known as the sign support, which consists of the vertical post and, if needed, any stiffeners onto which the sign panel is attached.
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