About 1,000 cubic yards of concrete were poured Thursday night and Friday morning for a deck for a rebuilt Fourth Avenue underpass.
The pour marks the halfway point for the $26 million project, which will result in a wider and taller underpass.
After the deck pour, crews will shift temporary tracks for Union Pacific Railroad and begin demolition of the south side of the old underpass in November.
When completed in spring 2009, the new underpass will accommodate one lane of motor vehicle traffic in each direction, and tracks for the Old Pueblo Trolley into downtown and, eventually, for a modern streetcar.
The underpass also will include lighted and elevated pedestrian walkways.
Tucson Department of Transportation officials estimate that it would take about 100 truckloads of concrete to complete the pour.