The 4th Avenue Underpass serves as a connection to downtown Tucson and historic Fourth Avenue. Sundt replaced Arizona’s oldest urban grade-separated roadway-railroad intersection, built in 1916, with a 250-foot-long reinforced concrete underpass for the City of Tucson’s Transportation Department.

Sundt constructed a shoofly to detour the Union Pacific Railroad during construction and completed extensive utility relocations for the project. Utility items included potable water, sanitary sewer and storm water and converting overhead power to underground power. The project team reconstructed parts of 4th Avenue, 5th Avenue, Congress Street and Broadway Boulevard, placed decorative concrete sidewalks and pedestrian plazas, and built retaining walls and steel pedestrian bridges. The project also included a public art component with construction of a multi-level fountain and pedestals for sculptures and landscaping.