Some of my very first days in RR employment were working as an 18-yr old ATSF switchman-brakeman (dual seniority) directly underneath the 6th Street bridge. The 6th Street switchtender worked alone, letting freights, transfers, etc. in and out of the First Street yard. You had to be very aware of the many First Class trains, including how to set up red blocks on the main line concurrent with lining a switch that would allow fouling either main. Your contact with the Yardmaster via radio was the only thing amounting to supervision... quite a lot of responsibility for a young newbie!

As an aside, there was an ungated concrete ramp underneath the bridge that led down to the concrete LA River bed, and on occasion (off duty of course) I took my motorcycle down to the river when no one was around. Some great memories from those days.