This historic underpass was built in 1916 and listed on the National Register of Historic Places. Things are about to change as the revitalization of Downtown Tucson moves forward.

".... A new underpass will be constructed to carry two lanes of traffic, two tracks for the historic trolley, two bicycle lanes and two wheelchair accessible sidewalks underneath the Union Pacific Railroad tracks.

The existing, historic Fourth Avenue Underpass will be refurbished with improved lighting and decorative paving and restricted to pedestrian use. Landscaped plazas will be constructed at both ends of the project..." Department of Highway website
The Greyhound Bus Station will be moved closer to I-10 and this final hurdle will allow the Underpass project and road realignment to finally begin.