Treatment of railroad ties with borate followed by over-treatment with creosote or copper naphthenate, called dual treatment, has become standard practice for ties being installed in higher decay hazard areas of the U.S. This paper provides an overview of why that has happened. Borate preservative presents very low human health and environmental risk. It diffuses through even hard to treat heart of hardwood ties, which is key in this application. Dual treated ties last twice or more as long as ties with only the primary preservative treatment in high decay hazard areas, resulting in substantial economic benefit to the railroads. Railroads should continue to specify borate dual treatment of new wooden ties while also using quality control practices to assure 0.25 pcf as DOT (or 4.05kg/m3) and full retention and sapwood penetration of oil borne over treatment.

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