The heading splits into non-impregnated (440611/440612) and impregnated (440691/440692) subheadings because preservative treatment — typically creosote or other wood preservatives — changes the product's durability profile and can affect applicable environmental or hazardous-material regulations at the port of entry. Misclassifying between these groups is a common audit finding.

Creosote is a registered pesticide in the US, and EPA regulations govern its use and handling. Importers of creosote-treated ties should verify compliance with EPA pesticide registration requirements and any applicable state-level restrictions before entry, in addition to standard customs documentation.