My new favorite picture in the world...
From Level junction in Wikipedia:
This temporary level junction allows Sacramento Southern Railroad trains to pass over the Union Pacific tracks in Sacramento, California. The components must be
installed, railroad cars moved, and the assembly dismantled in less than 30 minutes so as not to impede UPRR freight and Amtrak passenger train movement along the main line.
Photograph by Robert A. Estremo, copyright 2004.