450 was a portable substation car. For years it was positioned off West Colfax at Sheridan. It fed the Route 61 trolley line and also the Route 84(standard gauge) interurban.
When the Route 61 line was bussed, it was moved to Barnum Jct near Federal and 13th where this shot was taken. It was being pulled out as all street car service ended.
Courtesy the John Hammond photo