According to a an article named Economic Evaluation of Treated Wood and Galvanized Steel Guardrail Post published in 2013, the wooden post and spacer is moe cost effective than glavanized post and spacer in guardrail system.
Test data and experience in the paper indicate that preserved wood guardrail posts will provide service lives averaging approximately 50 years, equal to that expected of galvanized steel. With equal service life, treated wood guardrail posts and blocks support highway guardrail systems at approximately 60% of the cost of galvanized steel posts with composite blocks.
Contractor experience indicates wood posts are rarely damaged during installation and can usually be successfully reinstalled after removal. Steel posts typically are damaged by driving them into the ground, so most cannot be reused. As a result of their ability to be installed with minimal damage and the potential for direct reuse, in cases where early removal is involved, treated wood posts offer additional service life not possible with steel posts.
The annual cost of ownership to WSDOT for treated wood guardrail post systems is approximately $1,300 per year per mile of guardrail. The cost for equivalent steel post systems is approximately $2,300 per year per mile, or $1,000 more than for wood.
The cost of post systems are relatively small compared to the cost of the Type 31 W-Beam Guardrail at approximately $22 per linear foot ($116,000 per mile). WSDOT is unnecessarily spending more money by specifying only steel posts when equal service life and lower cost can be obtained by allowing competitive bidding of treated wood guardrail post systems.