Guardrail Posts Material Considerations

Guardrail post 01

Highway guardrail posts and signposts are integral to any well-traveled area. The Department of Transportation in each state has exacting standards for how they want their sign and guardrail posts constructed, and what materials they want them made from.

Many areas use wood posts, rather than metal, for this important job. Wood blends in naturally with the landscaping, and often has less of an environmental impact than some metals.

Wood Guardrail Posts versus Metal Guardrail Posts

Image Credit: travelandleisure.com

Not every municipality will use wood posts, but for many wood is the best and most natural choice. Sourcing local wood for sign posts or guardrail posts can have a better environmental impact than producing similar posts out of metal.

Metal posts may also have issues surrounding corrosion, and the need to treat the metal to ensure its longevity. This can often raise the cost of the project beyond the budget of the municipality, particularly in areas where multiple guardrails or sign posts are required at one time.

All highway sign posts need to be able to breakaway upon impact of a car in order to help reduce damage and loss of life. While rolled steel sign posts can be used, they need to be structurally modified in order to breakaway properly. This means that they need to weigh only 3lbs per linear foot and be installed no deeper than 42-inches deep.

In contrast, wood posts only need to have 3-inch holes drilled through them when they measure 6×8-inches in size; smaller posts do not need any modification to ensure that they will breakaway properly. This means that a wooden post will not only be less expensive, it will be easier for the municipality to inspect to ensure that the material is produced and installed properly.

Material Considerations for Wood Highway Posts

The key to using wood successfully in this area comes down to a few considerations. The first is the species of wood. In most cases, domestic wood is the best choice for these projects. There is less of an environmental impact, and shipping and delivery costs are less. 

Most wooden highway guardrail posts are made of Southern Yellow Pine, Red Pine, or Douglas Fir. These softwoods are environmentally responsible choices, as the trees they are harvested from regrow in far less time than hardwoods.

Your second consideration should be to what the wood is treated with. Softwoods should be treated in some way to help prevent water absorption and decay. 

There are several treatments available for softwoods, including:

  • CCA
  • Pentachlorophenol
  • Creosote
  • MCA
  • ACQ

These preservatives are necessary to help the posts get the longest amount of use. The posts maintain a natural color and appearance that helps them blend in with the local landscaping, but last much longer than untreated wood.

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