A Comparison of Pressure Treated Wood and Cedar SignpostsAuthor/Presenter: Griffith, Andrew
This report compares the use of pressure treated wood and cedar for signposts. Both materials are being used by the Oregon Department of Transportation (ODOT), however sign crews are now primarily using Port Orford cedar posts.
There are two types of pressure treated posts used by ODOT, Douglas-fir treated with Ammoniacal Copper Zinc Arsenate (ACZA) and Hem-fir treated with Chromated Copper Arsenate (CCA). There are environmental concerns about the use of pressure treated wood. However, studies cited in this report have shown it is not detrimental to the environment.
Based on price data provided by pressure treated wood suppliers, the purchase price for ACZA treated Douglas-fir is slightly higher than Port Orford cedar. Some of the suppliers expressed concerns about the availability of Hem-fir posts that would meet ODOT specifications.
The average disposal cost for pressure treated wood based on disposal at a landfill or waste transfer facility is slightly higher than cedar. In actual practice, sign crews dispose Port Orford cedar wastes in existing waste containers, thus eliminating the added disposal fee incurred by taking it directly to a landfill or waste transfer facility.
In a survey of ODOT sign crews, they unanimously favor using Port Orford cedar posts over pressure treated posts.
In Oregon State University’s wood post studies, Port Orford cedar posts lasted an average of 20 years, whereas pressure treated wood posts remained in service one-and-a-half to three times longer than Port Orford cedar. ODOT sign crews assert that only a small number of posts are replaced because of rotting, indicating a 20 year life is adequate for a signpost.
Based on the information presented in this report, Port Orford cedar is the most appropriate signpost material to meet ODOT requirements.