I-19 had originally been signed as it was constructed, in a series of small signing contracts that used customary units. In 1980, ADOT awarded a single contract to install new signs which used metric units, to overlay English-unit expressions on some existing signs with metric-unit expressions, to install kilometerposts, and to provide bilingual signing in select locations. The signing scheme used in 1980 provided explicit units on advance guide signs, but not on interchange sequence signs or post-interchange confirmation (distance) signs.