WATCH How Nampa and ITD divide responsibility for signs along state highwaysNampa and ITD divide responsibility for signs along state highwaysWithin Nampa, State Highways 45 and 55 pass through the city, along with Interstate 84 business loops. “We take care of 12th Avenue, which is Highway 45,” Robert Newman with the Nampa Traffic Division said. Along those routes, the Idaho Transportation Department remains responsible for speed limit signs and the black-and-white shields identifying the highways. Nampa maintains the other stop signs, one-way signs and traffic-flow signs, along with warnings, advisories and most other regulatory signs. It is also responsible for other city signage, including the Welcome to Nampa sign replaced in April through a project requested by late Mayor Rick Hogaboam.