The Vienna Convention on Road Signs and Signals required 15 states’ instruments of ratification or accession before its entry-into-force process could begin. Article 39 then provided that the convention would take effect after an additional 12-month period.
The treaty was opened for signature in Vienna on 8 November 1968. It sought to create a shared international vocabulary for road signs, traffic signals and road markings, building on earlier agreements while updating their standards.
“Ratification by 15 states” is the usual quiz answer, but the treaty’s legal wording is broader: it refers to instruments of ratification or accession. Ratification is a state’s formal approval after signing; accession is the way a state joins a treaty it did not sign during the original signature period.
The threshold should not be confused with the number of signatories. A country can sign without ratifying, and the United Nations separately lists signatories and parties. The convention ultimately entered into force on 6 June 1978, after the treaty’s conditions were satisfied.