A lot of this kind of all-metal construction was somewhat commonplace during the early portion of the 20th century, particularly for supporting heavy trolley cables.

Some of these pole lines lasted for many decades before so-called "upgrades" and/or metal base corrosion and rot got to them in northern climates owing to road salt, snow, ice, etc.

The metal crossarms you see still exist but they are rather scarce. Most of those that are still in service are atop their original metal poles that "survived" and have modern street lights connected to their bracket arms having long since replaced the very ornate glass-globed acrorn incandescent ones that graced them.